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All-optical switching of magnetization has great potential for use in future ultrafast and energy efficient nanoscale magnetic storage devices. So far, research has been almost exclusively focused on rare-earth based materials, which limits device tunability and scalability. Here, we show that a perpendicularly magnetized synthetic ferrimagnet composed of two distinct transition metal ferromagnetic layers, Ni3Pt and Co, can exhibit helicity independent magnetization switching. Switching occurs between two equivalent remanent states with antiparallel alignment of the Ni3Pt and Co magnetic moments and is observable over a broad temperature range. Time-resolved measurements indicate that the switching is driven by a spin-polarized current passing through the subnanometer Ir interlayer. The magnetic properties of this model system may be tuned continuously via subnanoscale changes in the constituent layer thicknesses as well as growth conditions, allowing the underlying mechanisms to be elucidated and paving the way to a new class of data storage devices.

FAPEMIG - Fundação de Amparo a Pesquisa do Estado de Minas Gerais Neste trabalho utilizamos técnicas de espectroscopia de absorção de raios X (XAS) para investigar aspectos estruturais e eletrônicos de dois sistemas com fortes correlações entre os elétrons. Estudamos a perovskita dupla desordenada BaTi(1/2)Mn(1/2)O(3) (BTMO) e o sistema intermetálico de férmions pesados Ce(2)Rh(1-x)Ir(x)In(8) (x=0.00, 0.25, 0.50, 0.75, 1.00) - Ce218. O BTMO foi recentemente investigado em nosso grupo de pesquisa em amostras volumétricas (estrutura hexagonal e grupo espacial R-3m), e revelou-se um sistema frustrado magneticamente em todo o intervalo de temperaturas medido. Nossos estudos também permitiram sugerir que o BTMO seja um candidato a líquido de spin. Neste trabalho, apresentamos os resultados quantitativos de XAS em amostras volumétricas e em filmes finos epitaxiais de BTMO. Nestes, que têm estrutura de perovskita simples com defeitos, observamos o aparecimento de magnetismo de longo alcance (ferro/ferri-magnético) nas temperaturas medidas, 5, 100 e 300 K, aparentemente associado com a mudança de dimensionalidade das interações magnéticas Mn-O-Mn. O sistema Ce218, por outro lado, foi estudado previamente por grupos colaboradores que mostraram o aparecimento de duas fases supercondutoras nesse composto: a fase SC1, observada na região rica em Rh e favorecida pela aplicação de pressão, e a fase SC2, observada em torno da concentração de Ir x ~ 0.6 e suprimida pela aplicação de pressão. Através de técnicas microscópicas nós mostramos que o sítio do Ir não apresenta desordem. Devido ao limite do fluxo do anel de luz síncrotron em energias da ordem de 24 keV, as medidas de absorção na borda K do Rh foram realizadas com baixa relação sinal-ruído, impossibilitando a análise confiável dos dados de EXAFS nessa borda. A análise dos dados experimentais foi realizada com simulações computacionais de espalhamentos múltiplos e cálculos de multipletos atômicos. No caso dos filmes finos de BTMO, crescidos pela técnica de Deposição por Laser Pulsado (PLD) sobre substratos de SrTiO(3) (STO 001), a caracterização física e química foi feita através de difração de raios X, mapeamento de espaço recíproco, medidas de magnetização, microscopia eletrônica de transmissão e microscopia de força atômica. In this work, we use X-ray absorption spectroscopy (XAS) techniques to investigate structural and electronic aspects of two systems with strong correlations amongst electrons. We studied the double disordered perovskite BaTi(1/2)Mn(1/2)O(3) (BTMO) and the heavy-fermion intermetallic system Ce(2)Rh(1-x) Ir(x)In(8) (x=0.00, 0.25, 0.50, 0.75, 1.00) - Ce218. BTMO was recently investigated in our research group on volumetric samples (hexagonal structure and space group R-3m, and it was characterized as magnetically frustrated throughout the measured temperature range. Studies also allowed us to suggest the BTMO as a candidate for the spin liquid. In this work, we present the quantitative results of XAS in BTMO bulk samples and epitaxial thin films. For the latter, we observed long-range magnetic order (ferro/ferri-magnetic) at 5, 100 and 300 K, apparently associated with the change in the dimensionality of the Mn-O-Mn magnetic interactions. The Ce218 system, on the other hand, was previously studied by collaborators. It was shown the appearance of two superconducting phases: the SC1 phase in the Rh-rich region, which is favored by applying pressure, and the SC2 phase, observed around the Ir concentration of x ~ 0.6, which disappears with applying pressure. With spectroscopic techniques we show that the Ir site has little structural disorder. Due to the limit of photon flux at energies of 24 keV, the XAS experiments at Rh K edge had low signal/noise ratio, making the analysis at the edge unreliable. We used EXAFS and XANES techniques together with computational simulations of multiple scatterings and atomic multiplet calculations. The BTMO thin films were epitaxially grown by Pulsed Laser Deposition (PLD) over SrTiO(3) (STO 001) substrates. We followed their chemical and physical details through X-ray diffraction, reciprocal space mapping, magnetization data, transmission electron microscopy, and atomic force microscopy. Tese (Doutorado)

This work addresses the growth of ultrathin magnetite (Fe3O4) and cobalt ferrite (CoFe2O4) films and their thorough structural, electronic, and magnetic characterization. In a first step, ultrathin Fe3O4 films are grown on SrTiO3(001) substrates by reactive molecular beam epitaxy (RMBE) and the substrate-induced anomalous strain behavior of the films is investigated by complementary high-resolution transmission electron microscopy (HRTEM) and (grazing incidence) X-ray diffraction [(GI)XRD] measurements. Next, an additional CoO film is deposited on similar Fe3O4/SrTiO3(001) heterostructures to demonstrate an alternative route for the synthesis of cobalt ferrite films through the thermally mediated interdiffusion of both oxide films. The evolution from the initial bilayer stacks to completely reacted cobalt ferrite films is extensively monitored by soft and hard X-ray photoelectron spectroscopy (soft XPS and HAXPES) and (GI)XRD. Complete intermixing and formation of single cobalt ferrite films is confirmed by angular-resolved HAXPES (AR-HAXPES) and X-ray reflectivity (XRR). The study of the cationic distribution resulting from this novel synthesis technique and its effects on the magnetic properties of the cobalt ferrite films is the subject of the subsequent part. Here, X-ray magnetic circular dichroism (XMCD) and superconducting quantum interference device (SQUID) magnetometry serve as key investigation techniques, which are further complemented by AR-HAXPES and atomic force microscopy (AFM) measurements. In a final step, highly crystalline cobalt ferrite films with different cationic stoichiometries are grown on MgO substrates using RMBE while their growth behavior is captured in real-time using operando XRD. Further structural characterization of the films is carried out by low-energy electron diffraction and XRR, whereas HAXPES and SQUID provide fundamental information on the electronic, chemical, and magnetic properties of the films.

Relaxation fundamentally determines the operation speed and energy efficiency of spintronic and spinorbitronic devices. We develop a theory of the longitudinal contribution to the relaxation of domain walls in ferromagnetic films of any thickness with the Dzyaloshinskii-Moriya interaction, which allows quantitative comparison with experiments. We show that the longitudinal contribution increases with a decrease of the transversal relaxation (e.g., the Gilbert constant). We predict a substantial enhancement of the contribution of the longitudinal relaxation to the damping of magnetic solitons with a decrease of the film thickness. We demonstrate that for ultrathin ferromagnetic films, the contribution of the longitudinal relaxation to the damping of domain walls is comparable to or stronger than any other traditional transversal mechanisms, including spin pumping. Although in this work we focus on the analysis of longitudinal relaxation for domain walls, in ultrathin samples it should be taken into account also for other magnetic solitons including skyrmions. This work adds to the fundamental understanding of the design and optimization of spintronic and spinorbitronic devices based on moving solitons in ultrathin films.

Magnonics is an emerging field in spintronics, aiming at the development of new-concept magnetic devices processing information via the manipulation of spin waves (SWs) in magnetic nanostructures. One of the most popular SW waveguides exploited currently is ferromagnetic nanostrips. Due to quantization caused by the lateral confinements, the dispersion of SWs propagating in a strip is characterized by a multi-branched structure. Consequently, SWs excited in the system involve superpositions of degenerate modes from different branches of the dispersion curves. In this work, we theoretically study the SW branch hybridization effect for two types of excitation methods, either by using a local oscillating magnetic field or a fast-moving field pulse. The former is based on the resonance effect and the latter on the Cherenkov-like emission mechanism. Micromagnetic simulations yield a variety of SW profiles with rather complex structures, which can be well explained by mode superpositions. These results draw attention to the significance of the SW branch hybridization effect when dealing with SWs in nanostrips and provide new aspects for the manipulation of SWs.

Binary magnetic alloys like Co–Pt are relevant for applications as components of magnetic exchange coupled composites. Numerous approaches exist to tune the coercive field of Co–Pt alloys primarily relying on high-temperature processing aiming to realize chemically long-range ordered phases. The peculiarity of Co–Pt is that large coercive field and magnetic anisotropy can be achieved even in chemically disordered alloys relying on short-range order. Here, we study alloying of Co–Pt from bilayers of Pt(14 nm)/Co(13 nm) at temperatures up to 550 °С, where bulk diffusion processes are suppressed and the dominant diffusion mechanism is grain boundary migration. We demonstrate that grain boundary diffusion mechanism can lead to the realization of a homogeneous yet chemically disordered Co56Pt44 alloy at temperatures of 500 °С and higher. A pronounced increase of the coercive field for samples processed at temperatures higher than 400 °С is attributed to short-range ordering. With this work, we pinpoint the grain boundary diffusion as the mechanism responsible not only for the homogenization of binary alloy films but also as a driving force for the realization of short-range order in Co–Pt. Our results motivate further research on grain boundary diffusion as a mechanism to realize chemically long-range ordered phases in Co–Pt alloys.

This work presents a magnetic field imaging method based on color centers in diamond crystal applied to a thin film of a nanolaminated Mn$_2$GaC MAX phase. Magnetic properties of the surface related structures have been described around the first order transition at 214 K by performing measurements in the temperature range between 200 K and 235 K with the surface features fading out by increasing temperature above the transition temperature. The results presented here demonstrate how Nitrogen-Vacancy center based magnetic microscopy can supplement the traditionally used set of experimental techniques, giving additional information of microscopic scale magnetic field features, and allowing to investigate the temperature dependent magnetic behavior. The additional information acquired in this way is relevant to applications where surface magnetic properties are of essence., Comment: 8 pages, 5 figures

Charged magnetic domain walls have been visualized in soft magnetic nanostructured Fe thin films under both static and dynamic conditions. A transition in the core of these zigzagged magnetic walls from N&eacute, el-type to Bloch-type through the formation of crosstie walls has been observed. This transition in charged zigzagged walls was not previously shown experimentally in Fe thin films. For film thicknesses t &lt, 30 nm, N&eacute, el-type cores are present, while at t &asymp, 33 nm, walls with crosstie cores are observed. At t &gt, 60 nm, Bloch-type cores are observed. Along with the visualization of these critical parameters, the dependence on the film thickness of the characteristic angle and length of the segments of the zigzagged walls has been observed and analyzed. After measuring the bistable magneto-optical behavior, the values of the wall nucleation magnetic field and the surface roughness of the films, an energetic fit to these nucleation values is presented.

Nanoporous Co40Fe40B20 (CoFeB) and sandwich tungsten (W)/CoFeB/W thin films were fabricated via an anodic aluminum oxide (AAO) template-assisted magneto sputtering process. Their thickness-dependent magneto-optical Kerr effect (MOKE) hysteresis loops were investigated for enhanced Kerr rotation. Control of the Kerr null points of the polarized reflected light can be realized via the thicknesses of the CoFeB layers and W layers. Simulation of the thickness-dependent phase difference change by the finite element method reveals the existence of the two Kerr null points for W/CoFeB/W thin films, matching the experimental result very well. However, there are two additional Kerr null points for pure CoFeB thin films according to the simulation by comparing with the experimental result (only one). Theoretical analysis indicates that the different Kerr null points between the experimental result and the simulation are mainly due to the enhanced inner magnetization in the ferromagnetic CoFeB layer with the increased thickness, which is usually omitted in the simulation. Clearly, the introduction of non-ferromagnetic W layers can experimentally regulate the Kerr null points of ferromagnetic thin films. Moreover, construction of W/CoFeB/W sandwich thin films can greatly increase the highest magneto-optical susceptibility and the saturated Kerr rotation angle when compared with CoFeB thin films of the same thickness.

Soft magnetic materials are used in integrated power magnetic devices (such as micro-inductors and micro-transformers) to achieve reasonable inductances at frequencies over a few megahertz. However, the out-of-plane (perpendicular) anisotropy, in thick films produced by vapor deposition, worsens the in-plane soft magnetic properties. This paper reports on the nano-lamination of Permalloy (Ni $_{81}$ Fe $_{19}$ ) thin films with the introduction of nitrogen-doped tantalum in between to eliminate the out-of-plane anisotropy and improve the in-plane anisotropy. This significantly improves the in-plane soft magnetic properties, reducing the coercivity from 1352 A/m to 25.5 A/m and increasing the anisotropy field from 180 A/m to 660 A/m. The high-frequency permeability was uniform up to 500 MHz, and the ferromagnetic resonance (FMR) frequency was increased to 1 GHz. These properties are ideal for high efficiency magnetic applications at high frequencies and an extended FMR frequency is imperative for gigahertz-range devices.

Amorphous rare-earth (RE) transition-metal (TM) alloys are ferrimagnetic (FiM) materials. In RE-TM, magnetic moments in RE and TM couples antiferromagnetically and form two magnetic sublattices. With the two sublattices, the magnetic properties of RE-TM thin films can vary significantly with temperature, composition, and thickness. For example, the magnetization of RE-TM alloys vanishes at the compensation temperature (Tcomp). Such flexibility has both advantages and disadvantages. On the one hand, their properties can be tuned for specific applications, such as magneto-optical recording devices and skyrmion based devices. On the other hand, with so many tunable parameters, it could be very time consuming to optimize their properties experimentally. Guidance from simulations can provide crucial knowledge to reduce the time and the cost of experiments. This thesis focuses on the tuning of magnetic properties in RE-TM thin films through simulations and experiments. Based on experimental results, computational models are developed. Then, simulations results can be used to guide experiments. In this study, RE- TM thin films were deposited on various substrates by radio frequency (RF) magnetron sputtering at room temperature. In TbFeCo on thermally oxidized Si substrates, the exchange bias effect was revealed near Tcomp. Magnetic modeling was needed to investigate the origin of the exchange bias effect. To study this effect, the micromagnetic model is adopted into the two-sublattice model, where each sublattice evolves under its own Landau-Lifshitz-Gilbert (LLG) equation. Using the two-sublattice model, exchange interactions between two nanoscale amorphous phases were found to be the origin of the exchange bias. Using this model, one can explore different FiM heterostructure to develop desirable exchange bias properties for applications at room temperature. In addition to exchange bias, the ability to control magnetic anisotropy can provide great flexibility in writing and storing information. Using TbFeCo deposited on Kapton, the magnetic properties of TbFeCo are varied through the bending of Kapton. Furthermore, in VO2/TbFeCo heterostructure, a decrease in magnetic anisotropy in TbFeCo was found to correspond to the tensile strain from the structural transition of the underlying VO2 films. These results provide guidance on tuning magnetic anisotropy through interfacial strain. Amorphous RE-TM thin films are also promising materials for hosting magnetic skyrmions, which are proposed for magnetic memory devices to improve density and efficiency. In RE-TM thin films, skyrmions are stabilized through the interfacial Dzyaloshinskii-Moriya Interaction (DMI), originates from an adjacent heavy metal layer. In this study, computational models are employed to investigate room-temperature skyrmions in GdCo thin films. Using atomistic simulations, various parameters, including thickness, composition, anisotropy, and interfacial DMI, are varied to explore their effects on skyrmions. Results show that increasing thickness and reducing interfacial DMI in GdCo can further reduce the size of skyrmion at room temperature, which is crucial for applications.

Important applications of spin polarized low energy electron microscopy (SPLEEM) employ this technique's vector imaging capability to resolve domain wall (DW) spin textures. Studying several thin film systems including Co/W(110), Co/Cu(001) and (Co/Ni)n/W(110), we show that an additional contrast can appear at magnetic DWs. By imaging the magnetization as a function of electron landing energy, electron energies are selected at which the magnetic domain contrast vanishes. Surprisingly, under such conditions of zero contrast between magnetic domains, we observe the appearance of magnetic contrast outlining the DWs. This DW contrast does not depend on the DW spin texture. Instead, our measurements show that this DW contrast results from a combination of the energy-dependence of the spin reflectivity asymmetry of the magnetic film, the finite energy width of the spin polarized electron source, and the dispersion of the magnetic prism array that separates the illumination and imaging columns of the instrument. Awareness of this DW contrast mechanism is useful to aid correct interpretation of SPLEEM images.

The paper is focused on the development and optimization of strontium ferrite nanomaterial and photosintered flexible thin films. These magnetic thin films are characterized with direct current (DC) and high frequency measurements. For photosintered strontium ferrite samples, we achieved relative complex permeability of about 29.5-j1.8 and relative complex permittivity of about 12.9-j0.3 at a frequency of 5.9 GHz.

A MnxGa1-x (x=0.70) epitaxial thin film with perpendicular magnetic anisotropy and a large coercivity (mu H-0(c) =1 T) was patterned into nanodots using a combined self-assembly nanolithography and plasma etching procedure. Nanostructuring is achieved by self-assembly of polystyrene nanospheres acting as a mask on the magnetic film. This procedure allows easy patterning of a large area although introduced some chemical disorder, which resulted in a soft magnetic component in the magnetic hysteresis loops. However, chemical order was recovered after vacuum annealing at low temperature. The resulting nanodots retain the properties of the original film, i.e. magnetization oriented perpendicular to the particle and large coercivity. Our results suggest this lithography procedure could be a promising direction for nanostructuring tetragonal Heusler alloys. (C) 2016 Elsevier B.V. All rights reserved.

Materials science has been intensively developed during the last 30 years. This is due, on the one hand, to an increasing demand of new materials for new applications and, on the other hand, to technological progress which allows for the synthesis of materials of desired characteristics and to investigate their properties with sophisticated experimental apparatus. Among these advanced materials, magnetic materials at nanometric scale such as ultra thin films or ultra fine aggregates are no doubt among the most important for electronic devices.In this review, we show advanced theoretical methods and solved examples that help understand microscopic mechanisms leading to experimental observations in magnetic thin films. Attention is paid to the case of magnetically frustrated systems in which two or more magnetic interactions are present and competing. The interplay between spin frustration and surface effects is the origin of spectacular phenomena which often occur at boundaries of phases with different symmetries: reentrance, disorder lines, coexistence of order and disorder at equilibrium. These phenomena are shown and explained using of some exact methods, the Green's function and Monte Carlo simulation. We show in particular how to calculate surface spin-wave modes, surface magnetization, surface reorientation transition and spin transport., To appear in JSAMD

A general equation describing the motion of domain walls in a magnetic thin film in the presence of an external magnetic field has been reported in this paper. The equation includes all the contributions from the effects of domain wall inertia, damping and stiffness. The effective mass of the domain wall, the effects of both the interaction of the DW with the imperfections in the material and damping have been calculated.

Co/Ni multilayers ordered according to a periodic, Fibonnacci and Thue Morse sequence have been obtained by Atomic Layer Deposition and a subsequent process of thermal reduction. The morphology of the multilayers was investigated by scanning electron microscopy, while longitudinal hysteresis curves were obtained by magneto-optical magnetometry of Kerr effect. The morphology of the films varies as a function of their sequence and thickness. Multilayers exhibit coercivities much higher than expected from samples synthesized with other methods. The control of the magnetic properties of multilayers, as a function of their sequence, may allow their use in spintronic devices., This work was supported by Fondequip (refs. EQM120045, EQM140092 and EQM160155), Fondecyt (refs. 1200302, 3180042 and 1201491), Basal Project (ref. AFB180001) and Universidad Central (ref. CIP2018006).

A growing variety of microelectronic devices and magnetic field sensors as well as a trend of miniaturization demands the development of low-dimensional magnetic materials and nanostructures. Among them, soft magnetic thin films of Finemet alloys are appropriate materials for sensor and actuator devices. Therefore, one of the important directions of the research is the optimization of thin film magnetic properties. In this study, the structural transformations of the Fe73.5Nb3Cu1Si13.5B9 and Fe72.5Nb1.5Mo2Cu1.1Si14.2B8.7 films of 100, 150 and 200 nm thicknesses were comparatively analyzed together with their magnetic properties and magnetic anisotropy. The thin films were prepared using the ion-plasma sputtering technique. The crystallization process was studied by certified X-ray diffraction (XRD) methods. The kinetics of crystallization was observed due to the temperature X-ray diffraction (TDX) analysis. Magnetic properties of the films were studied by the magneto-optical Kerr microscopy. Based on the TDX data the delay of the onset crystallization of the films with its thickness decreasing was shown. Furthermore, the onset crystallization of the 150 and 200 nm films began at the temperature of about 400&ndash, 420 &deg, C showing rapid grain growth up to the size of 16&ndash, 20 nm. The best magnetic properties of the films were formed after crystallization after the heat treatment at 350&ndash, 400 &deg, C when the stress relaxation took place.

Magnetic cobalt-gold thin films (Co Au(1_)) are grown on silicon (100) surfaces by using a sputter deposition technique. Magnetic anisotropy of the films is investigated by ferromagnetic resonance (FMR). Magnetic properties are explored by micromagnetic simulations based on the metropolis algorithm. Effective magnetic anisotropy is gradually increased with Co concentration. In-plane axial anisotropy exists for all samples and it is enhanced with a Co concentration of similar to 40% corresponding optimal cluster size, and intercluster separation. Segregation and coalescence of Co clusters caused by different Co concentrations strongly affect magnetic properties of the thin films. Therefore, the study revealed that magnetic behavior of Co Au(1-x) thin films can be tuned by changing Co concentration.

The Spin-Torque Nano-Oscillators (STNOs) have been attracting tremendous attention as an innovative nano-scale microwave signal generator for modern electronics systems. The key features include large range of frequency tunability, nanoscale size and compatibility with standard silicon technology. This work explored different magnetic multilayers both from the material perspective and the device aspect with an ultimate goal to lower the critical current density of spin torque switching and to create coherent spin torque oscillation with output power towards the µW range. The major task of this dissertation was to establish the benchmark for spin-torque nano-oscillators fabricated using the Bias Target Ion Beam Deposition (BTIBD) technique and the photolithography techniques. A Co2FeAl/Cr/Co2FeAl trilayer was evaluated to have a small MR ratio ~0.07% at room temperature. The small MR ratio will severely affect the output voltage and impede its application on spin-transfer oscillation devices. Optimizations were made on CFA/Cu/CFA and nano-oxide layer(NOL)/CFA/Cu/CFA multilayers to improve the MR ratio. Significant enhancement of MR ratio was observed in the NOL/CFA/Cu/CFA pseudo spin valve (PSV) due to the specular reflection from the NOL. The origin of the magnetoresistance in single layer L10 MnAl was studied by linking the resistivity change to the domain wall (DW) scattering of charge carriers. Quantitative analysis on remanent states’ MFM images and the corresponding resistivity confirmed the contribution of DWs to the electric resistivity of MnAl. Magnetic static and magneto transport properties for a magnetic hybrid multilayer configuration CFA/Cr/MnAl have been investigated for the purpose of spin transfer study. Low room temperature MR ratio of ~0.05% was observed on the hybrid PSV possibly due to the small spin-polarization in the thin MnAl films. From the device perspective, DC current induced magnetization reversal and magnetization oscillation was observed in 500 nm large size Co90Fe10/Cu/Ni80Fe20 pillars. A perpendicular external field enhanced the coercive field separation between the reference layer (Co90Fe10) and free layer (Ni80Fe20) in the pseudo spin valve, allowing a large window of external magnetic field for exploring the free-layer reversal. A magnetic hybrid structure was achieved for the study of spin torque oscillation by applying a perpendicular field > 3kOe. The magnetization precession was manifested in terms of the multiple peaks on the differential resistance curves. Depending on the bias current and applied field, the regions of magnetic switching and magnetization precession on a dynamical stability diagram has been discussed in details. Micromagnetic simulations are shown to be in good agreement with experimental results and provide insight for synchronization of inhomogeneities in large sized device. The ability to manipulate spin-dynamics on large size devices could be proved useful for increasing the output power of the spin-transfer nano-oscillators (STNOs).

Electroless deposition technology has been considered as a kind of common ways to obtain cobalt alloy films. However, in order to get cobalt alloy films, high temperature (353 K) is necessary during the electroless deposition process which will increase costs and energy consumption. Ultrasonic was introduced during electroless plating process to obtain cobalt alloy films at lower initial temperature. It was found that the cobalt thin films could be prepared at lower initial temperature (323 K) with the introduction of ultrasonic. Therefore, different powers of ultrasonic were applied during the electroless deposition process to prepare CoP thin films on copper substrates from an alkaline bath in this investigation. The effects of different powers of ultrasonic on deposition rate, surface morphology, anticorrosion performance and magnetic property of films were studied. It was found that the deposition rate increased gradually with the rise in ultrasonic powers due to cavitation phenomenon. All the CoP lilms presented the typical spherical nodular structures with the impact of ultrasonic. Smaller and regular shaped structures could be observed when the films were deposited with higher power of ultrasonic which contributed directly to enhancement of anticorrosion performance. Saturation tnagnetization and coercivity of thin films increased gradually with the rise in ultrasonic powers during the electroless deposition process due to the higher amounts of cobalt. (c) 2014 Chinese Materials Research Society. Production and hosting by Elsevier B.V. All rights reserved.

We report the experimental and theoretical study of a substrate roughness surface induced magnetic anisotropy in thin films of Fe and Co. The experimental results confirm previously reported data on NiFe thin films and indicate that rough substrates increase the magnetic coercive fields in magnetic thin films. This effect is most prominent in films of thickness comparable to the surface roughness values and materials of small volume magnetic anisotropy. We determined the coercive field of 15 nm Fe thin film sample deposited onto rough PVDF to be 256 Oe, which is more than doubled the value of the coercive field of 15 nm Fe films coated under identical conditions, onto smooth Si substrates. The effect is visible for Co films but weaken by its increased volume magneto-crystalline anisotropy. These results are important for applications based on magnetic thin film where the magnetic properties could be adjusted via substrate roughness engineering.

The excitation of spin waves by a microwave current injected into a coplanar waveguide with finite-width ground lines on a continuous Permalloy film is investigated both experimentally and numerically. Phase sensitive micro-focused Brillouin light scattering has been employed to reveal the spatial profile of the propagating spin waves in the magnetostatic surface wave geometry. The experimental results have been satisfactorily reproduced by means of micromagnetic simulations. The exciting microwave field used in this simulation has the spatial profile defined by the coplanar waveguide and user-defined periodic boundary conditions were employed in order to simulate the extended system. The resulting space and time dependent evolution of the magnetization has been analyzed by means of one and two dimensional fast Fourier transform algorithm in order to obtain the spatial profile and the frequency spectrum of the excited spin waves as well as their dispersion relations. Evidence is given to asymmetric emission from the two sides of the coplanar waveguide due to the symmetry breaking related to the sense of precession of the dynamical magnetization, as well as to the near-field effects of the extended spin wave emitter.

In this work, we study magnetic thin films presenting magnetic stripe patterns. A fingerprint of such domains is a linear behavior of the in-plane magnetization curves below a given saturation field. We present free energy models for the in-plane magnetization curves which permit us to extract key geometrical information about the stripe patterns, such as the maximum canted angle of the magnetization and the domain wall width. As an example, we discuss in this work magnetization curves for Fe1-xGax magnetic films which present a stripe pattern with a period of 160 nm and we found a typical maximum canted angle of and a domain wall width around 30 nm. Fil: Di Pietro Martínez, Marisel. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentina Fil: Milano, Julian. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina. Laboratorio Internacional Franco-Argentino en Nanociencias; Argentina Fil: Eddrief, M.. Laboratorio Internacional Franco-Argentino en Nanociencias; Argentina. Sorbonne Universités; Francia. Centre National de la Recherche Scientifique; Francia Fil: Marangolo, M.. Laboratorio Internacional Franco-Argentino en Nanociencias; Argentina. Sorbonne Universités; Francia. Centre National de la Recherche Scientifique; Francia Fil: Bustingorry, Sebastián. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina

The dynamics of magnetic domain walls in ultrathin strip-patterned Pt/Co/AlOx samples with perpendicular easy axis has been studied experimentally under an easy-axis field, superposed to a hard-axis field oriented along the strip. The easy-axis field is large so that the domain walls move well beyond the creep regime. A chiral effect is observed where the domain wall velocity shows a monotonous and surprisingly large variation with an in-plane field. A micromagnetic analysis, combining analytic, one-dimensional, and two-dimensional simulations with structural disorder, shows that this behavior can be reproduced with a Dzyaloshinskii-Moriya interaction of the interfacial type, with due consideration of the dynamics of the tilt degree of freedom of the domain wall. The estimated effective value of this interaction ($D\ensuremath{\approx}\ensuremath{-}2.2\phantom{\rule{0.28em}{0ex}}\mathrm{mJ}/{\mathrm{m}}^{2}$ for a 0.6 nm Co thickness) is consistent with values obtained by other techniques. It is also shown, by micromagnetic analysis, that several modes and characteristic times occur in the dynamics of the tilt of such domain walls.

In this paper we report structural, magnetic and transport properties of strongly textured Ni51Mn36Sn13 thin films. The off-stoichiometric Heusler alloy films with 200 nm thickness were sputter-deposited on a MgO(100) substrate at 500 K and after annealed at 1000 K in UHV conditions. The textured growth was confirmed by x-ray diffraction in Bragg-Brentano geometry. The temperature dependence of the magnetic properties was measured by VSM and FMR methods. The electron transport measurements were carried out in function of temperature in 0 Oe and 50 kOe fields. All measurements corroborate the existence of the martensitic transformation in the film. Furthermore, transport measurements reveal an influence of the magnetic field on the transition temperature.

Fe-Pt thin films were deposited by rf sputtering on an MgO substrate heated at different temperatures to induce the formation of the perpendicular Fe-Pt L1(0) phase with a different grain morphology on the nanometer scale. All films are characterized by amaze like pattern of FePt nanograins with interconnected bases. MFM images and magnetization curves indicate that all samples have a strong perpendicular magnetic anisotropy arising from (0 0 1) growth. The temperature behaviour of the electrical resistance indicates that a percolating path exists for conduction electrons in the mazelike pattern. The magnetoresistance was measured as a function of magnetic field (applied longitudinally) and temperature in the ranges -70 kOe < H < +70 kOe and 4 K < T < 150 K, respectively. All samples display a complex behaviour of the electrical resistance as a function of applied field. The role of the different magnetoresistance effects (both intrinsic and extrinsic) measured in these FePt thin films is elucidated. (C) 2010 Elsevier B.V. All rights reserved.

Here, we report the effect of A-site substitution of Tb at the expense of Bi on the ferroelectric and magnetic properties in m = 5 layered 2-D Aurivillius Bi6Ti3Fe2O18 thin films. The nominal stoichiometry of the prepared compound is Tb0.40Bi5.6Fe2Ti3O18, Tb0.90Bi5.1Fe2Ti3O18, and Bi6Ti3Fe2O18. Phase examination reveals that only 0.40 mol. % is successfully substituted forming Tb0.40Bi5.6Fe2Ti3O18 thin films. Lateral and vertical piezoresponse switching loops up to 200 °C reveal responses for Bi6Ti3Fe2O18, Tb substituted Tb0.40Bi5.6Fe2Ti3O18, and Tb0.90Bi5.1Fe2Ti3O18 thin films along the in-plane (±42.31 pm/V, 88 pm/V and ±134 pm/V, respectively) compared with the out-of-plane (±6.15 pm/V, 19.83 pm/V and ±37.52 pm/V, respectively). The macroscopic in-plane polarization loops reveal in-plane saturation (Ps) and remanence polarization (Pr) for Bi6Ti3Fe2O18 of ±26.16 μC/cm2 and ±22 μC/cm2, whereas, ±32.75 μC/cm2 and ±22.11 μC/cm2, ±40.30 μC/cm2 and ±28.5 μC/cm2 for Tb0.40Bi5.6Fe2Ti3O18 and Tb0.90Bi5.1Fe2Ti3O18 thin films, respectively. No ferromagnetic signatures were observed for Bi6Ti3Fe2O18 and Tb0.40Bi5.6Fe2Ti3O18. However, a weak response was observed for the Tb0.90Bi5.1Fe2Ti3O18 at 2 K. Microstructural analysis of Tb0.90Bi5.1Fe2Ti3O18 revealed that it contains 4 vol. % Fe:Tb rich areas forming FexTbyOz, which accounts for the observed magnetic moment. This study demonstrates the importance of thorough microstructural analysis when determining whether magnetic signatures can be reliably assigned to the single-phase system. We conclude that Tb0.40Bi5.6Fe2Ti3O18 and Tb0.90Bi5.1Fe2Ti3O18 samples are not multiferroic but demonstrate the potential for Fe-RAM applications.

We present Monte Carlo simulation data about Holmium magnetic thin film structures. As well known, this rare earth shows, at transition temperature T N , a helical order in the bulk phase. In contrast with the collinear ferromagnetic or antiferromagnetic thin films, recent experimental works have proven that the transition temperature T N ( n ) ( n being the film thickness) depends on n only by an empirical relation. In order to study the behavior of these film structures, we consider a Heisenberg model with easy-plane single ion anisotropy and seven coupling constant ( J 0 in the plane and J 1 − J 6 between plane of the Ho h c p structure), obtained by experimental neutron measurements.

Copyright © Indian Academy of Sciences. The magnetic properties of Ni thin films, in the range 20–500 nm, at the crystalline-nanocrystalline interface are reported. The effect of thickness, substrate and substrate temperature has been studied. For the films deposited at ambient temperatures on borosilicate glass substrates, the crystallite size, coercive field and magnetization energy density first increase and achieve a maximum at a critical value of thickness and decrease thereafter. At a thickness of 50 nm, the films deposited at ambient temperature onto borosilicate glass, MgO and silicon do not exhibit long-range order but are magnetic as is evident from the non-zero coercive field and magnetization energy. Phase contrast microscopy revealed that the grain sizes increase from a value of 30–50 nm at ambient temperature to 120–150 nm at 503 K and remain approximately constant in this range up to 593 K. The existence of grain boundary walls of width 30–50 nm is demonstrated using phase contrast images. The grain boundary area also stagnates at higher substrate temperature. There is pronounced shape anisotropy as evidenced by the increased aspect ratio of the grains as a function of substrate temperature. Nickel thin films of 50 nm show the absence of long-range crystalline order at ambient temperature growth conditions and a preferred [111] orientation at higher substrate temperatures. Thin films are found to be thermally relaxed at elevated deposition temperature and having large compressive strain at ambient temperature. This transition from nanocrystalline to crystalline order causes a peak in the coercive field in the region of transition as a function of thickness and substrate temperature. The saturation magnetization on the other hand increases with increase in substrate temperature. University Grants Commission for Centre of Advanced Studies in Physics

A complete magneto-optical characterization of Pt capped Ag-Co-Ag sputtered trilayers with varying Co thickness is presented. Polar Kerr rotation and ellipticity exhibit a gradual increase in signal as the Co layer gets thicker, with a sharp feature around 3.75 eV due to the bulk Ag plasmon resonance. The transverse Kerr signal of such trilayers is strongly affected by the surface plasmon polariton (SPP) resonance excitation when measured in the Kretschmann configuration, with a maximum transverse Kerr effect for around 2 nm Co thickness which corresponds to the optimum SPP excitation. This behavior is in contrast with the monotonous increase in transverse Kerr signal with Co thickness measured when the SPP is not excited. These results are in qualitative agreement with simulations using the transfer matrix formalism, the discrepancies mainly being due to the deviation from 2-D growth of the system and possible Ag and Co oxidation effects., This work was supported in part by the Spanish Ministry of Science and Education under NAN2004-09195-C04-01 and MAT2005-05524-C02-01, in part by the Comunidad de Madrid (Ref. S-0505/MAT/0194), in part by the CSIC (Refs.200650I130, 200650I032, and 2005MX0040), and in part by CONACYT-México grants 48300 S-3907 and J110.474/2006 S-3904. The authors are grateful to D. Ramírez and G. Ramírez for technical assistance.

This doctoral work is focused on the study of nanostructured magnetic materials by advanced transmission electron microscopy (TEM) techniques, with emphasis on Ni2MnGa shape memory alloy thin films and magnetite nanoparticles for biomedical applications. The combination of high-resolution transmission electron microscopy and electron diffraction to characterize morphology and crystalline structure, with Lorentz microscopy and Electron Holography, permits to achieve a deep insight in the structural and magnetic nano-characterization of magnetic nanostructured materials. The work, carried out at the CNR-IMEM institute of Parma and partially at the LMA-INA institute of Zaragoza in the framework of the Erasmus Placement, produced remarkable results concerning the correlation between the microstructure of these systems and their magnetic/functional properties, from nano-to micro-to macro scale. In detail, the main topics treated are: 1) The use of Lorentz microscopy to investigate the role of dipolar interaction on hyperthermia of magnetic nanoparticles. Magnetic nanoparticles (NPs) in the superparamagnetic state are suitable for both diagnostic and therapeutic approaches. In particular, the magnetic hyperthermia, performed applying radiofrequency magnetic fields, can be effectively employed to locally induce cancer cell death. In real systems, clusters of magnetic nanoparticles with different size can form and the dipolar interactions that arise among nanoparticles can strongly influence the heating ability of the colloidal suspension. The role of the dipolar interactions in the hyperthermic behaviour of the system, however, is still not completely understood. About this topic, an investigation about magnetite nanoparticles with different degrees of interaction was carried out by Lorentz microscopy in a TEM. With this technique, it was possible to visualize and map the inter-particle interactions and to develop reliable models on the power losses mechanisms for different nanoparticles aggregates. As a result, a deeper understanding of the interactions effects on the performance of different nanoparticles suspensions as hyperthermic mediators was obtained. All the TEM results were supported and complemented by conventional o macroscopic (?) magnetic characterization. 2) Employment of advanced TEM techniques to study the effect of epitaxial strain and film thickness in the twin variants formation in Ni2MnGa martensitic thin films In martensitic thin films, the martensitic phase transition gives rise to a poly-twinned system characterized by a complex microstructure in which two families of twin variants can be displayed, with different magnetic anisotropies. Both the use of different substrates and film thickness can significantly modify the twin variants formation and consequently alter their functional properties. High-resolution TEM (HRTEM), Selected Area Electron Diffraction (SAED) and Electron Holography was employed to fully characterize Ni2MnGa thin films in plan and cross section geometries, by variyng film thicknesses in the range 50-100 nm and substrate type (MgO, MgO/Cr buffer layer). The structural and magnetic properties at the nano-micro scale were obtained by comparing TEM analysis with the morphological, structural and magnetic properties on a larger scale (by atomic force microscopy(AFM) , X-ray diffraction (XRD) and magnetic force microscopy (MFM)). A model for the twin variants selective formation, based on the stress states induced by the different substrates and film thicknesses, is moreover proposed. The model represents a powerful tool to selectively control the twin variants formation in martensitic films with low thicknesses and to tailor their magnetic domains structure. 3) An in depth TEM characterization to study the role of microstructure on magnetically induced reorientation of twin variants in Ni2MnGa 200 nm thin films In Ni2MnGa alloys, giant strains, one order of magnitude higher than the typical magnetostriction and state-of-the-art piezoelectric values, can be obtained by a magnetomechanical effect based on twin variants reorientation induced by magnetic field (MIR). Therefore, the possibility of exploiting the martensitic distortions to create tiny machines while keeping simple design, and high actuation frequencies makes these materials particularly appealing for the integration in active microsystems. However, very limited MIR effects were found in thin films and a full comprehension and exploitation of the effect is still lacking. An in-depth TEM characterization to correlate the crystal structure to the twin variants configurations and the magnetism inside each domain of the Ni2MnGa alloys is proposed by the combination of different advanced TEM techniques such as High Angle Annular Dark Field (HAADF) imaging, HRTEM with the comparison of the experimental images to the simulated ones, SAED, Electron Holography and magnetic domain analysis by in-situ observation. A model based on TEM results, compared with the findings obtained by XRD, AFM, MFM and magnetization curves, has been finally suggested to explain the anisotropic microstructure formation in a 200 nm thick Ni2MnGa film grown on MgO/Cr, displaying a huge anisotropic MIR. The proposed model is crucial for the engineering of the martensitic microstructure and for achieving substantial values of MIR in constrained films. 4) TEM study of the reduction of dimensionality in martensitic Ni2MnGa systems: from thin films to sub-micrometric disks After gaining a good understanding of the microstructure of two-dimensional NiMnGa martensitic films with relation to their application properties, the last chapter is devoted to test the possibility to obtain new functional properties by scaling down the dimensionality of these systems. To this aim, the in-depth TEM characterization was extended to a novel class of nanostructures, Ni2MnGa nano-disks, to investigate the structural and magnetic properties of the disks and the effect of the lateral confinement on the martensitic phase. By employing HRTEM, Lorentz microscopy and electron diffraction analysis as a function of temperature with heating holder, the actuation mechanisms, which remain active with the dimensionality reduction, can be studied. La presente tesi di dottorato è focalizzata sullo studio di materiali magnetici nanostrutturati tramite tecniche avanzate di microscopia elettronica in trasmissione (TEM), con particolare attenzione su film sottili a base della lega metallica Ni2MnGa, materiale magnetico a memoria di forma, e nanoparticelle di magnetite per applicazioni biomediche. La combinazione delle tecniche di microscopia elettronica in alta risoluzione e di diffrazione elettronica con le tecniche di microscopia di Lorentz e olografia elettronica, permette di ottenere un’approfondita conoscenza delle proprietà magnetico-strutturali di materiali magnetici nanostrutturati. Il presente lavoro, svolto principalmente all’istituto IMEM-CNR di Parma and parzialmente presso il laboratorio LMA-INA di Saragozza, ha prodotto importanti nuovi risultati riguardanti la correlazione tra la microstruttura e le proprietà magnetiche/funzionali di questi sistemi, dalla nanoscala alla micro/macro scala. In dettaglio, i punti più importanti in cui il lavoro è stato articolato sono: 1) Utilizzo della microscopia di Lorentz per l’investigazione riguardante il ruolo delle interazioni dipolari nell’ipertermia magnetica di nanoparticelle di magnetite. Nanoparticelle magnetiche (NPs) nello stato superparamagnetico sono molto promettenti sia nel campo diagnostico, che terapeutico. In particolare, l’ipertermia magnetica, realizzata tramite l’applicazione di un campo magnetico alle radiofrequenze, può essere efficace nell’induzione locale della morte di cellule tumorali. In sistemi di nanoparticelle reali, cluster di nanoparticelle magnetiche con differenti dimensioni possono crearsi grazie alle interazioni dipolari, che possono anche fortemente influenzare la capacità di generazione di calore da parte della sospensione colloidale. Il ruolo delle interazioni dipolari nel comportamento ipertermico del sistema, comunque, non è ancora stato del tutto chiarito. Riguardo questo argomento, uno studio su nanoparticelle di magnetite con differenti gradi di interazioni è stato condotto tramite microscopia elettronica in trasmissione usando la tecnica di microscopia di Lorentz. Con questa tecnica, è possibile visualizzare e mappare le interazioni dipolari tra le particelle e sviluppare modelli attendibili riguardo i meccanismi di perdita di energia per differenti aggregati di nanoparticelle. Come risultato di questo studio, è stata ottenuta una più approfondita comprensione degli effetti indotti dalle interazioni dipolari sulla performance di diversi aggregati di nanoparticelle magnetiche come mediatori ipertermici. Le caratterizzazioni e i risultati conseguiti tramite microscopia TEM sono fortemente supportati dalle caratterizzazioni magnetiche convenzionali. 2) Utilizzo di tecniche avanzate di microscopia elettronica in trasmissione per lo studio degli effetti dovuti a strain epitassiale e spessore del film nella formazione delle varianti di twin in film sottili martensitici di Ni2MnGa. In film sottili martensitici, la transizione di fase martensitica produce una complessa microstruttura rappresentata da un sistema poli-twinnato, in cui due famiglie di varianti di twin con differenti anisotropie magnetiche possono essere comunemente osservate. Sia l’impiego di differenti substrati e/o di buffer-layers come la variazione dello spessore del film, possono pesantemente modificare la formazione delle varianti di twin e conseguentemente alterare le proprietà funzionali dei film stessi. Le tecniche di microscopia elettronica in alta risoluzione (HRTEM), di diffrazione elettronica da area selezionata (SAED) e olografia elettronica sono state impiegate per ottenere una completa caratterizzazione dei film sottili di Ni2MnGa in visione planare ed in sezione trasversale, per film con uno spessore variabile nel range 50-100 nm e con differenti substrati (MgO, MgO/buffer layer di Cr). Le proprietà strutturali e magnetiche alla scala nano-micrometrica sono state ottenute comparano l’analisi TEM con la morfologia e le proprietà strutturali e magnetiche su una scala più ampia (ottenute tramite l’utilizzo di tecniche di: microscopie a scansione di sonda (AFM/MFM), diffrazione di raggi X (XRD). Un modello per la formazione selezione selettiva di varianti di twins, basato sullo stato di stress indotto dai differenti substrati e in funzione dei diversi spessori dei films, è stato inoltre proposto. Questo modello rappresenta un potente strumento per controllare la formazione selettiva delle varianti di twin in film martensitici caratterizzati da bassi spessori e, conseguentemente, permette di controllare la loro struttura a domini magnetici. 3) Caratterizzazione, tramite microscopia elettronica in trasmissione, del ruolo della microstruttura sulla ri-orientazione magnetica delle varianti di twin in film sottili di Ni2MnGa spessi 200 nm. Nelle leghe Ni2MnGa, enormi strain con valori un ordine di grandezza più grandi rispetto a quelli osservati tipicamente nei materiali piezoelettrici, possono essere ottenuti grazie ad un effetto magnetomeccanico basato sulla ri-orientazione delle varianti di twin indotta da un campo magnetico applicato (effetto MIR). Le possibilità di sfruttare la distorsione indotta nella fase martensitica per creare piccoli sistemi di attuazione tenendo un design semplice e di compiere cicli di attuazione ad alte frequenze rendono quindi questi materiali particolarmente attraenti per l’integrazione in microsistemi di attuazione. Tuttavia, effetti MIR molto limitati sono stati osservati in film sottili e una completa comprensione e controllo dell’effetto è tuttora mancante. Una caratterizzazione approfondita per correlare la struttura cristallina alle configurazioni di varianti di twins ed il magnetismo di ogni dominio della lega Ni2MnGa è proposto, tramite l’impiego combinato di differenti tecniche avanzate di microscopia elettronica in trasmissione come imaging con detector anulare ad alto angolo (HAADF), HRTEM con il confronto delle immagini sperimentali a quelle simulate, SAED, olografia elettronica, analisi dei domini magnetici tramite osservazione in-situ. Un modello basato sui risultati ottenuti dalla caratterizzazione TEM, confrontati con i risultati sperimentali ottenuti tramite XRD, AFM, MFM e caratterizzazioni magnetiche, è stato inoltre proposto per spiegare l’orientazione preferenziale della microstruttura in film di Ni2MnGa di 200 nm, cresciuti su MgO/Cr e mostranti un enorme effetto MIR anisotropico. I risultati conseguiti sono di cruciale importanza per l’ingegnerizzazione della microstruttura martensitica e per l’ottenimento di un rilevante effetto MIR in film sottili vincolati al substrato. 4) Studio tramite microscopia elettronica in trasmissione degli effetti della riduzione di dimensionalità in sistemi martensitici Ni2MnGa: dal film sottile al disco sub-micrometrico. Un’approfondita analisi TEM è stata condotta su una nuova classe di materiali nanostrutturati, i nanodischi di Ni2MnGa, per la caratterizzazione delle proprietà strutturali e magnetiche dei dischi e l’effetto del confinamento laterale della fase martensitica. Combinando le tecniche di HRTEM, microscopia di Lorentz e diffrazione elettronica in funzione della temperatura, è possibile scoprire quali sono i meccanismi di attuazione che sopravvivono alla riduzione della dimensionalità.

Köçkar, Hakan (Balikesir Author), A novel rotating cryostat vacuum system originally designed to fabricate organic layers has been used for the first time to evaporate 3% silicon-iron magnetic materials. Results of all films deposited on glass and silicon exhibit isotropic magnetic behaviour but the films produced on kapton generally show an in-plane magnetic anisotropy within the film plane. Results were also confirmed with the laser-ablated films.

Particulate double-layer tape samples with magnetic underlayers have been investigated by performing magnetic recording measurements and by computer simulation.The presence of soft-magnetic underlayers resulted in decreased signal output and better overwrite behavior. Hard-magnetic underlayers showed the opposite result.

Copper ferrite thin films have been prepared by RF sputtering on quartz substrates. By following successive heating and quenching, it was possible to obtain the films, which showed cubic phase in X-ray diffraction. The grain size was found to be similar to 30 nm. The magnetization was observed to be of the order of 3000 G with a coercivity of 480 Oe. (C) 2002 .

Epitaxial thin films of MnxGa1−x (x = 0.70, 0.74) grown on single crystal (LaAlO3)0.3(Sr2TaAlO6)0.7 [LSAT] substrates exhibit an enhanced magnetic moment and magnetic anisotropy in comparison to films of the same composition grown epitaxially on SrTiO3 [STO] single crystal substrates. Atomic and magnetic force microscopy revealed films exhibiting uniform grains and magnetic domain structures, with only minor differences between the films grown on different substrates. High resolution transmission electron microscopy on the x = 0.74 sample grown on LSAT showed a well-ordered, faceted film structure with the tetragonal c-axis oriented out of the film plane. Further, misfit dislocations, accommodating the lattice mismatch, were evidenced at the film/substrate interface. The out of plane c lattice parameter is larger for all x in the films grown on LSAT, due to the smaller substrate lattice parameter compared to STO. The increase in c generates a larger distortion of the tetragonal lattice which promotes the enhanced magnetization and magnetocrystalline anisotropy. These results indicate that LSAT is a promising substrate for realizing highly tailored magnetic properties for future spintronic applications not only in MnxGa1−x but also in the broader class of tetragonal Mn-Z-Ga (Z = transition metal) materials.

Spin-Torque-Transfer Magnetic Random Access Memory (STT-MRAM) has the potential to become a universal memory due to its superior properties compared with conventional memory technologies. However, the main challenge for implementing STT writing mode in high-density and high-speed memory is the substantial reduction of the intrinsic current density Jc0 required to switch the magnetization of the free layer (FL) while maintaining high thermal stability required for long-term data retention. The intrinsic switching current reduction can be pursued by using materials with low saturation magnetization (Ms), low damping constant (α), high spin polarization (η) and high magnetic anisotropy energy density (Ku) at low dimension. Previous experiments showed that CoFeB incorporated in MgO-based MTJ is one of the most efficient materials for this purpose. In this work chromium was substituted into CoFeB alloys to further reduce their magnetization attributed to the antiferromagnetism of Cr. Films in composition of Cr at 30% showed a reduced magnetization of 300 emu/cm3 and an enhanced coercive field of 500 Oe, making this material suitable for device application. Moreover, the switching current density Jc0 is predicted to be reduced significantly by using materials with perpendicular magnetic anisotropy (PMA), compared with the normal in-plane ones. Perpendicular Magnetic anisotropy was found in crystalline D022 Mn2.5Ga films with optimal magnetic anisotropy energy of 0.5 ×107 erg/cm3, which leads to high thermal stability. A low saturation moment (Ms = 260 emu/cc) was investigated, attributed to the strong antiferromagntic coupling between Mn atoms at different sites. With a reported high spin polarization of 88%, D022- Mn2.5Ga film has the potential to be used in spintronic devices. Amorphous ferrimagnetic GdxFe93-xCo7 films were also found to exhibit low magnetization and perpendicular magnetic anisotropy, which is attributed to the competition between antiferromagnetic coupling of rare-earth (RE) with transition-metal (TM) ions and ferromagnetic interaction between the TM ions. Furthermore, low magnetization was achieved at room temperature in previously unreported high-Gd region of x=52-59, accompanied by a large PMA with coercivity reaching ~6.6 kOe. Our findings have broadened the composition range of transition metal-rare earth alloys for designing PMA films, making it attractive for tunable magnetic anisotropy in nanoscale devices. In addition to Ms and η, one can also reduce FL intrinsic damping constant for lowering Jc0, but practically PMA films often have higher damping constant α due to strong spin-orbit coupling. With reported low damping constant of 0.0025, CoFeGe film is promising spintronic material. Perpendicular magnetic anisotropy was achieved in the MgO/CoFeGe/MgO structure with an optimized magnetic anisotropy energy density of 2 106 erg/cm3, which is contributed by the interfacial anisotropy between CoFeGe and MgO. The B2-ordered CoFeGe is not half metallic but has a perfectly spin-polarized ∆1 band along the [001] direction, thus the perfect spin transfer efficiency with MgO barrier is expected in CoFeGe-base MTJs.

Using X-ray photoelectron emission microscopy we have observed the coexistence of ferromagnetic and antiferromagnetic phases in a (3 at.%)Pd-doped FeRh epilayer. By quantitatively analyzing the resultant images we observe that as the epilayer transforms there is a change in magnetic domain symmetry from predominantly twofold at lower temperatures through to an equally weighted combination of both four and twofold symmetries at higher temperature. It is postulated that the lowered symmetry Ising-like nematic phase resides at the near-surface of the epilayer. This behavior is different to that of undoped FeRh suggesting that the variation in symmetry is driven by the competing structural and electronic interactions in the nanoscale FeRh film coupled with the effect of the chemical doping disorder., Comment: 10 pages, 8 figures, 1 table

An advanced deposition technique known as glancing angle deposition (GLAD) [K. Robbie, J. C. Sit, and M. J. Brett, J. Vac. Sci. Technol. B 16, 1115 (1998); K. Robbie and M. J. Brett, U.S. Patent No. 5,866,204 (filed 1999)] has been used to fabricate periodic arrays of magnetic pillars and randomly seeded magnetic helices, posts, and chevrons. Because of the nature of initial film nucleation, the GLAD process normally distributes posts randomly on the substrate surface. We can grow periodic arrays of GLAD microstructures by suppressing the randomness inherent within the initial nucleation stage of film growth. Shadowing sites were fabricated by pre-patterning a thin titanium layer on silicon substrates into a square array using electron beam lithography. These sites shadow regions of the substrate from incident flux during film deposition and act as preferred nucleation sites for film growth. Using this process, we have fabricated periodic arrays of cobalt posts with a regular elemental period of 600 nm and post diameters and heights of 300 and 400 nm, respectively. Randomly seeded posts, helices, and chevrons were also fabricated. The mean separation for the randomly seeded posts was 350 nm with individual post diameters of 100�150 nm, while the separations for the helices and chevrons were less than 100 nm. X-ray diffraction, transmission electron microscopy, and a dc superconducting quantum interference device magnetometer were used to analyze the magnetic and crystal properties of both the periodic and randomly seeded arrays. A newly developed three-dimensional ballistic deposition simulator was used to simulate the growth of the periodic post arrays in order to better understand the growth mechanisms., 46th National Symposium of the American Vacuum Society

The magnetic anisotropies of obliquely evaporated Co films were studied using ferromagnetic resonance. The coercive force (H/sub c/) increases rapidly beyond the incidence angle of /spl eta/=60/spl deg/. The remanence ratio (M/sub r//M/sub s/) along the parallel axis at 0/spl deg/ is 0.55-0.7 and comes to a minimum at /spl eta/=30--60/spl deg/. For 1000-/spl Aring/ films deposited at /spl eta/=75/spl deg/, oblique anisotropy field of H/sub k1/=4.9 kOe, in-plane anisotropy field of H/sub k2/=3 kOe and tilt angle of /spl alpha/=28/spl deg/ were observed; this film has H/sub c/=800 Oe and M/sub r//M/sub s/=0.95.

A general framework for the domain size in any ultrathin film with perpendicular magnetic anisotropy is here discussed. The domain structure is analyzed by using the classical theory taking into consideration the demagnetization field contribution to the domain wall energy. A sinusoidal model is considered to describe the domain structure while approaching, in two different cases, the monodomain state with in-plane magnetization. The first case is realized applying a large enough in-plane magnetic field. The second one is obtained by decreasing the perpendicular magnetic anisotropy, which is connected in many ultrathin systems with the increase of film thickness. A change in the domain size of several orders of magnitude is obtained while approaching the magnetization reorientation region. The minimal stripe domain period p=8πlex2/d is calculated from the sinusoidal model, where lex is the exchange length and d is the thickness of the film. The range of possible domain size changes in ultrathin films is predicted. The domain size has been experimentally studied in a 1 nm Co film characterized by a square hysteresis loop. The investigations have been performed by polar Kerr based microscopy and magnetic force microscopy. The domain structure of two remnant states generated by applying an in-plane and a perpendicular magnetic field has been compared. Drastically, the smallest domain size has been observed for the former., The authors are grateful to Professor J. Miltat for fruitful discussions concerning MFM imaging and Dr. M. Tekielak for magneto-optical imaging. J. M. Garcia wishes to thank the European Community for his Marie Curie Fellowship. This work was supported by the Polish State Committee for Scientific Research (Grant No. 4 T08A 025 23), ESF NANOMAG project and European Commission program ICA1-CT-2000-70018 (Center of Excellence CELDIS).

We have studied the optical and magneto-optical components of the light scattered by the surface of several Fe films with different morphologies. We present a method, based on the ratio between the optical and magneto-optical components of the scattered intensity, to discern the physical origin, either structural or magnetic corrugation, of the light scattered by these ferromagnetic surfaces. Surface versus bulk magnetic information can be separated by magneto-optical light scattering measurements, the scattered light being more sensitive to magnetization differences between surface and bulk than the reflected one., This work was performed under Spanish CICyT financial support. One of the authors (M.U.G.) thanks the Consejería de Educación y Cultura de la Comunidad de Madrid for funding. One of the authors (C.M.B.) acknowledges a grant from the Ministerio de Ciencia y Tecnología.

Summary form only given. Non-linear properties of magnetostatic surface spin wave (MSSW) pulses in ferrite-dielectric-metal (FDM) structures have been studied experimentally. All experiments were performed with the pure YIG film separated from the metal plate by an air gap with the thickness t /spl ap/ 100/spl mu/m or t /spl ap/ 200/spl mu/m. Film parameters were: the thickness d /spl ap/ 14/spl mu/m, the width /spl omega/ = 2mm, the length l /spl ap/ 18mm, and ferromagnetic resonance line-width /spl Delta/H /spl ap/ 0.3Oe. The bias field was varied in the range 890-1100 Oe. It has been found that the MSSW with the wavelength /spl lambda/ comparable with the dielectric spacer thickness t is unstable for both self-modulation and parametric instabilities, while MSSW with /spl lambda/ t is unstable only for the last one. It was measured a pulse narrowing due to the bright soliton formation at frequencies in the "negative" slope region of the MSSW dispersion in the FDM structure. We have also found a strong influence of parametric instability on pulse propagation and, for this reason, we concluded that parametric instability and self-modulation are in competition.

Magnetic thin films based on iron group elements (Fe, Co, Ni) are currently used in computer's hard disk drives and in MEMS, whereas electrodeposition is a suitable method to obtain these materials. The powders of metals and alloys were obtained by electrochemical deposition at constant current density using alkaline ammonium electrolyte which consist one, two or three different elements Co, Ni and Mo. Ni and Co are deposited anomalously. The Mo element cannot be obtained electrochemically from the aqueous solutions. Electrochemical deposition of this metal is induced by codeposited iron-group metals, Ni and Co, for instance. This study investigates the influence of electrochemical parameters on composition and properties of obtained powders. Based on the obtained experimental results, it could be concluded that the particle size of deposited powders and chemical composition are influenced by the chemical composition of the electrolyte, with changing the concentration ratio of ions of metallic salts as well as current density imposed. As a consequence, the changes in magnetic properties are obvious. The structure and morphology of powders were investigated by Scanning Electron Microscopy (SEM). For demonstration of mechanism of powder deposition Image ProPlus software for SEM microphotograph analysis was used. The values of individual objects as well as formed clusters of powders were measured by this technique. The chemical composition of the powders was determinate using Energy Dispersive X-ray (EDX) analysis. XRD results suggested that obtained powders were of amorphous structure.

The magnetization behavior of a Permalloy thin-film (nominally Ni81Fe19) was investigated as a function of combined quasistatic and pulsed magnetic fields measured using magneto-optic Kerr effect magnetometry. We observed complex field dependent switching behavior that depends on the relative contributions to the total field of the quasistatic and pulsed fields. As the pulsed field amplitude was increased, complex switching behavior occurs for total fields in excess of the coercive field. A simple phenomenological domain wall propagation model suggests a qualitative understanding of this complex behavior based on Walker breakdown of the domain wall motion occurring in the Permalloy thin-film.

The deposition of a dielectric overlayer on top of Au/Co/Au multilayer films can significantly enhance the magnetic field induced modulation of the surface plasmon polariton (SPP) wave vector. This enhancement is analyzed as a function of the thickness of the dielectric overlayer and the associated SPP electromagnetic field confinement and redistribution. The decrease in SPP propagation distance is taken into account by analyzing an adequate figure of merit., We acknowledge funding from the EU (Grant No. NMP3-SL-2008-214107 Nanomagma), the Spanish MICINN (“MAGPLAS” Grant No. MAT2008-06765-C02-01/NAN,“FUNCOAT” CONSOLIDER INGENIO 2010 Grant Nos.CSD2008-00023, and MAT2005-05524-C02-01), the Comunidad de Madrid (“NANOBIOMAGNET” Grant No. S2009/MAT-1726 and “MICROSERES-CM” Grant No. S2009/ TIC-1476), CSIC (Grant No. 200850I187), and Deutsche Forschungsgemeinschaft (Grant No. TE770/1).

We correlate simultaneously recorded magnetotransport and spatially resolved magneto optical Kerr effect (MOKE) data in Co2FeAl Heusler compound thin films micropatterned into Hall bars. Room temperature MOKE images reveal the nucleation and propagation of domains in an externally applied magnetic field and are used to extract a macrospin corresponding to the mean magnetization direction in the Hall bar. The anisotropic magnetoresistance calculated using this macrospin is in excellent agreement with magnetoresistance measurements. This suggests that the magnetotransport in Heusler compounds can be adequately simulated using simple macrospin models, while the magnetoresistance contribution due to domain walls is of negligible importance.

Via a direct coupling between the order parameter and the singlet Josephson supercurrent we detect spin-wave resonances and their dispersion in ferromagnetic Josephson junctions in which the usual insulating or metallic barrier is replaced with a weak ferromagnet. The coupling arises within the Fraunhofer interferential description of the Josephson effect because the magnetic layer acts as a time-dependent phase plate. A spin-wave resonance at a frequency ${\ensuremath{\omega}}_{s}$ implies a dissipation that is reflected as a depression in the current-voltage curve of the Josephson junction when $\ensuremath{\hbar}{\ensuremath{\omega}}_{s}=2eV$. We have thereby performed a resonance experiment on only ${10}^{7}$ Ni atoms.

Electric field-controlled ferromagnetism of (Zn,Co)O is demonstrated via anomalous Hall effect measurements. The electron carrier concentration in this material is 1.65× 1020 cm-3 as measured via ordinary Hall effect at 4 K, and an anomalous Hall effect is observed up to 6 K, but with no hysteresis at any temperature. With positive electric gate field, the carrier concentration is increased by approximately 2%, resulting in a clear magnetic hysteresis at 4 K. The ability to reversibly induce/eliminate ferromagnetism by applied gate field alone, measured via the effect on the carriers, is a clear sign of carrier-induced ferromagnetism in this system. © 2009 American Institute of Physics.

Thin films of TbMnO3 have been grown on SrTiO3 substrates. The films grow under compressive strain and are only partially clamped to the substrate. This produces remarkable changes in the magnetic properties and, unlike the bulk material, the films display ferromagnetic interactions below the ordering temperature of ~40K. X-ray photoemission measurements in the films show that the Mn-3s splitting is 0.3eV larger than that of the bulk. Ab initio embedded cluster calculations yield Mn-3s splittings that are in agreement with the experiment and reveal that the larger observed values are due to a larger ionicity of the films., Comment: REVTeX, 5 two-column pages, 4 EPS figures