Search

The solid solubility of the isomorphous monosilicides during the silicide reaction of Ni-Pt, Ni-Pd and Pt-Pd alloys on Si(100) is comparatively studied in the full composition range. Our study reveals that PtSi and PdSi, exhibiting a minor lattice mismatch, directly form a solid solution. In contrast, for larger differences in lattice parameters such as is the case for NiSi-PtSi and NiSi-PdSi, the mutually soluble phases coexist, prior to the formation of a solid solution at increased temperatures. Hence, it appears that the direct formation of a ternary monosilicide solid solution is inherently related to the lattice mismatch of the binary monosilicides. This finding provides an explanation for important differences observed in the elemental redistribution between the three systems, considered to be very similar up to now. Moreover, the different formation of a solid solution results in a fundamentally different nucleation of PdSi: while Ni lowers the nucleation barrier by reducing the contribution of the interface energy, Pt strongly increases the entropy of mixing which triggers the formation of the Pd-monosilicide at surprisingly low temperatures. Our results show that the lattice mismatch is a crucial parameter and determines the phase formation sequence and elemental redistribution during the silicide reaction.

The recent demonstration of ferroelectricity in ultrathin HfO

We used lithographically fabricated nanoconstrictions made of Ag–Co granular thin films to achieve current densities above 10 A/cm during magnetotransport measurements. Systematically measured variations of the resistance with current under high applied magnetic fields did not reveal any dramatically large magnetoresistance effect, in contrast to the previous observations using mechanical point contact based techniques. Our experimental results on resistance switching by current injection in the Ag–Co nanoconstrictions reveal spin torque effects. The switching amplitudes are considerably smaller when compared to the results obtained for pillar shaped trilayers due to the large number of Co grains in the nanoconstrictions. We demonstrate that the use of point contact patterns with nanometer dimensions, where effects resulting from current induced mechanical distortions at high magnetic fields are negligible, has obvious advantages over the mechanical point contact technique for studying spin injection effects.

The structure, magnetic properties, and lattice dynamics of ordered Fe–Pt alloys with three stoichiometric compositions, Fe 3 Pt, FePt and FePt 3 , have been investigated using the density functional theory. Additionally, the existing experimental data have been complemented by new measurements of the Fe projected phonon density of states performed for the Fe 3 Pt and FePt 3 thin films using the nuclear inelastic scattering technique. The calculated phonon dispersion relations and phonon density of states have been compared with the experimental data. The dispersion curves are very well reproduced by the calculations, although, the softening of the transversal acoustic mode TA 1 leads to some discrepancy between the theory and experiment in Fe 3 Pt. A very good agreement between the measured spectra and calculations performed for the tetragonal structure derived from the soft mode may signal that the tetragonal phase with the space group P 4/ mbm plays an important role in the martensitic transformation observed in Fe 3 Pt. For FePt 3 , the antiferromagnetic order appearing with decreasing temperature has been also investigated. The studies showed that the phonon density of states of FePt 3 very weakly depends on the magnetic configuration.

Indium tin oxide (ITO) is broadly used as a transparent conducting material for electrodes in optoelectronic devices. Irradiation of ITO with low energy ions can result in the formation of periodic surface nanopatterns which can serve as an alternative for the polymer alignment layer in liquid crystal devices. We investigated the formation of the ion-induced surface nanopatterns on ITO with focus on the influence of the crystalline structure of the material. We find that the crystallinity plays a crucial role in the pattern formation, with no pattern developing on an amorphous ITO surface. We discuss these findings in the context of the state-of-the-art theory for ion-induced patterning. We show that the ion-induced pattern plays a critical role in the liquid crystal alignment on ITO surfaces.

The coexistence of superconductivity and ferromagnetism is investigated in granular Sn-Co nanocomposites. The nanocomposites have been prepared by co-deposition of Sn atoms and Co clusters, the morphology and composition of which can be tuned by varying the deposition rate of Co clusters relative to Sn atoms. Flat isolated Sn islands are obtained at zero or low Co cluster flux, while granular nanocomposites are formed with increasing Co cluster flux, reaching Co concentrations up to 44 vol.%. Interfaces with a low electronic transparency between superconductor and ferromagnet are obtained by a combination of the granular nature of the nanocomposites and the formation of Sn-Co alloys at the Sn/Co interfaces. The structure and composition of the nanocomposites have been thoroughly characterized by atomic force microscopy, x-ray diffraction and conversion electron Mössbauer spectroscopy. Over the entire Co concentration range, the hybrids show a ferromagnetic response. The superconducting phase boundary and the Meissner response depend on the morphology and composition of the nanocomposites. In particular, the superconducting critical temperature decreases with increasing Co concentration, while the Meissner response varies from a reversible to a strongly hysteretic behaviour depending on the morphology of the samples with different Co content. The persistence of superconductivity at high Co concentrations is attributed to a suppression of the superconducting proximity effect in these nanocomposites, which is ascribed to the low interface transparency between the Sn and Co components that make up these hybrid systems. publisher: Elsevier articletitle: Coexistence of superconductivity and ferromagnetism in cluster-assembled Sn–Co nanocomposites journaltitle: Journal of Alloys and Compounds articlelink: http://dx.doi.org/10.1016/j.jallcom.2015.03.007 content_type: article copyright: Copyright © 2015 Elsevier B.V. All rights reserved. ispartof: Journal of Alloys and Compounds vol:637 pages:509-516 status: published

A new strategy to elaborate (1-3) type multiferroic nanocomposites with controlled dimensions and vertical alignment is presented. The process involves a supported nanoporous alumina layer as a template for growth of free-standing and vertically aligned CoFe

Surface treatments using multiple Ar ion irradiation processes with a maximum energy and fluence of 200 keV and 1 × 10 16 ions/cm 2 , respectively, have been performed on two different metallic glasses: Zr 55 Cu 28 Al 10 Ni 7 and Ti 40 Zr 10 Cu 38 Pd 12 . Analogous irradiation procedures have been carried out at room temperature (RT) and at T = 620 K (≈0.9 T g , where T g denotes the glass transition). The structure, mechanical behavior, wettability and corrosion resistance of the irradiated alloys have been compared with the properties of the as-cast and annealed ( T = 620 K) non-irradiated specimens. While ion irradiation at RT does not significantly alter the amorphous structure of the alloys, ion irradiation close to T g promotes decomposition/nanocrystallization. Consequently, the hardness ( H ) and reduced Young’s modulus ( E r ) decrease after irradiation at RT but they both increase after irradiation at 620 K. While annealing close to T g increases the hydrophobicity of the samples, irradiation induces virtually no changes in the contact angle when comparing with the as-cast state. Concerning the corrosion resistance, although not much effect is found after irradiation at RT, an improvement is observed after irradiation at 620 K, particularly for the Ti-based alloy. These results are of practical interest in order to engineer appropriate surface treatments based on ion irradiation, aimed at specific functional applications of bulk metallic glasses.

The magnetic and electric properties of impurities in semiconductors are strongly dependent on the lattice sites which they occupy. While the majority site can often be predicted based on chemical similarities with the host elements and is usually simple to confirm experimentally, minority sites are far more complicated to predict, detect and identify. We have carried out extensive β − emission channeling studies on the lattice location of transition metal impurities in wide-gap dilute magnetic semiconductors, namely Co and Mn in GaN and ZnO, making use of radioactive 61 Co and 56 Mn implanted at the ISOLDE facility at CERN. In addition to the majority occupation of cation (Ga, Zn) sites, we located significant fractions (of the order of 20%) of the Co and Mn impurities in anion (N, O) sites, which are virtually unaffected by thermal annealing up to 900 °C. Here, we present the β − emission channeling experiments on 61 Co-implanted GaN. We discuss these results in the context of our recent reports of minority anion substitution in Mn-implanted GaN Pereira et al. (2012) [19] and Mn/Co-implanted ZnO Pereira et al. (2011) [20] , particularly in terms of the advantages of the emission channeling technique in such cases of multi-site occupancy.

Homopolymers as nanocarriers for the loading of block copolymer micelles with metal salts: a facile way to large-scale ordered arrays of transitionmetal nanoparticles Lianchen Shan,1 Sathya Punniyakoti,1 Margriet J. Van Bael,2 Kristiaan Temst,3 Marlies K. Van Bael,4 Xiaoxing Ke,5 Sara Bals,5 Gustaaf Van Tendeloo,5 Marc D'Olieslaeger,1,6 Patrick Wagner,1,6 Ken Haenenaf and Hans-Gerd Boyen*1,6 [ 1 ] Hasselt Univ, Inst Mat Res IMO, B-3590 Diepenbeek, Belgium [ 2 ] Katholieke Univ Leuven, Lab Solid State Phys & Magnetism, B-3001 Louvain, Belgium [ 3 ] Katholieke Univ Leuven, Inst Kern Stralingsfys, B-3001 Louvain, Belgium [ 4 ] Hasselt Univ, Inst Mat Res, B-3590 Diepenbeek, Belgium [ 5 ] Univ Antwerp, Electron Microscopy Mat Res EMAT, B-2020 Antwerp, Belgium [ 6 ] Imec Vzw Div IMOMEC, B-3590 Diepenbeek, Belgium A new and facile approach is presented for generating quasi-regular patterns of transition metal-based nanoparticles on flat substrates exploiting polystyrene-block-poly2vinyl pyridine (PS-b-P2VP) micelles as intermediate templates. Direct loading of such micellar nanoreactors by polar ransition metal salts in solution usually results in nanoparticle ensembles exhibiting only short range order accompanied by broad distributions of particle size and inter-particle distance. Here, we demonstrate that the use of P2VP homopolymers of appropriate length as molecular carriers to transport precursor salts into the micellar cores can significantly increase the degree of lateral order within the final nanoparticle arrays combined with a decrease in spreading in particle size. Thus, a significantly extended range of materials is now available which can be exploited to study fundamental properties at the transition from clusters to solids by means of well-organized, well-separated, size-selected metal and metal oxide nanostructures. ispartof: Journal of Materials Chemistry C vol:2 issue:4 pages:701-707 status: published

In this article we present a detailed investigation of the structural and magnetic properties of exchange biased NiFe (ferromagnet)/FeMn (antiferromagnet) thin films. The influence of the shape anisotropy on exchange bias and the magnetization reversal mechanism in a sample with patterned lines is compared with a continuous two-dimensional reference sample. Polarized neutron reflectivity (PNR) is employed to study the magnetization reversal by analyzing the spin-flip and non-spin-flip reflectivities. PNR measurements show that the magnetization reversal in the reference two-dimensional film and patterned lines is by domain wall motion rather than coherent rotation of magnetization.

We investigated the reversal mechanism in a Co/CoO exchange bias bilayer with a pronounced magnetocrystalline anisotropy in the ferromagnet. The anisotropy, which is induced by the growth of a highly textured Co layer, imposes a distinct reversal mechanism along the magnetically easy and hard direction. It is shown that exchange bias can be induced along both directions, despite the magnetocrystalline anisotropy. The interplay between the magnetocrystalline anisotropy and exchange bias induces a different reversal mechanism for the subsequent reversals in the two crystallographic directions. Along the hard axis, the magnetization reverses according to the reversal mechanism observed before in polycrystalline exchange bias bilayers, i.e. domain wall nucleation and motion for the first reversal and coherent rotation for the subsequent ones. Along the easy axis, domain wall motion remains the dominant reversal mechanism and magnetization rotation has only a minor contribution.

This paper reports on the advantage of using artificial neural networks (ANNs) to analyze large sets of real-time Rutherford backscattering spectrometry (RBS) data. Real-time RBS, i.e. collecting RBS spectra at periodic time intervals during a thermal treatment, probes the full response of a thin film to the annealing in situ . Although very valuable insights can be gained by this technique, the time-consuming analysis of the vast amount of RBS spectra acquired during real-time RBS measurements has so far prevented the widespread use of real-time RBS. Setting up an ANN is quite an intensive process as well, but once trained, these ANNs can handle the analysis of large data sets practically instantaneously. As such, the beneficial combination of real-time RBS and ANN analysis forms a perfect synergy. In this test case, a network was trained and applied to analyze the Ni silicide growth during annealing of a thin 80 nm Ni film on Si(1 0 0). The ANN performance was validated by comparing the ANN results with the conventional analysis performed on the same data set.

We present a study of the transport properties of films consisting of Co n clusters embedded in a Au matrix for different Co cluster concentrations. The films were prepared by low-energy cluster beam deposition of Co clusters, combined with simultaneous thermal evaporation of Au. By varying the deposition rates of both Co clusters and Au, films with different Co concentrations were obtained. We investigated the influence of the Co concentration on the low-temperature resistance behavior, thus probing the dominant scattering mechanisms determining the film resistance. The change in low-temperature resistance behavior reveals a transition from films with a low Co concentration, where the low-temperature resistance is dominated by phonon scattering to increasingly ferromagnetically behaving films, in which electron–electron interactions are dominant. The Debye temperature of the films was found to scale with the Co concentration in the films. The low-temperature electron mean free path was determined, which allowed to investigate the influence of the film granularity on the resistance. The temperature dependence of the resistivity reflects the increasing granularity as Au is gradually replaced by Co grains.

Epitaxial multiferroic BaTiO₃-BiFeO₃ composite thin films exhibit a correlation between the magnetoelectric (ME) voltage coefficient αME and the oxygen partial pressure during growth. The ME coefficient αME reaches high values up to 43 V/(cm·Oe) at 300 K and at 0.25 mbar oxygen growth pressure. The temperature dependence of αME of the composite films is opposite that of recently-reported BaTiO₃-BiFeO₃ superlattices, indicating that strain-mediated ME coupling alone cannot explain its origin. Probably, charge-mediated ME coupling may play a role in the composite films. Furthermore, the chemically-homogeneous composite films show an oxygen vacancy superstructure, which arises from vacancy ordering on the {111} planes of the pseudocubic BaTiO₃-type structure. This work contributes to the understanding of magnetoelectric coupling as a complex and sensitive interplay of chemical, structural and geometrical issues of the BaTiO₃-BiFeO₃ composite system and, thus, paves the way to practical exploitation of magnetoelectric composites. ispartof: Materials vol:9 issue:1 pages:1-13 ispartof: location:Switzerland status: published

Magnetization reversal in exchange biased Co/CoO dot arrays has been investigated systematically as a function of shape anisotropy, dot size, temperature, cooling field and training effect. Polycrystalline 24?nm Co films have been sputtered on a pre-patterned Si/SiO2 substrate with the lateral dimensions of the dots varying from 200 to 900?nm at a fixed spacing of 800?nm. The Co dots have been oxidized using pure oxygen to create a Co/CoO bilayer. Below the N?el temperature, the hysteresis loop of this bilayer displays a normal unidirectional shift due to the exchange bias in the continuous film, while the patterned film displays an additional anomaly of the upper part of the hysteresis loop. This anomaly, which is shape dependent, increases with decreasing temperature and cooling field. On the other hand, it decreases for the trained loops with increasing aspect ratio (length/width) of the patterned dot. This anomaly is probably caused by incomplete biasing due to the competition between magnetostatic inter-dot interactions and exchange bias.

The influence of patterning on exchange bias has been investigated using arrays of micron-sized Co/CoO dots with different lateral confinement and length-to-width ratio. The patterned samples show higher coercive and exchange bias fields than a continuous Co/CoO bilayer. As in unpatterned film, magnetization reversal mechanisms on opposite sides of the hysteresis loops of the microstructured samples are different. However, with the increase of lateral confinement and shape anisotropy of the dots, the asymmetry in the magnetization reversal starts to differ from that observed in continuous Co/CoO films.

Patterned Co/CoO thin film structures have been investigated by magnetization and polarized neutron reflectivity measurements in order to study the influence of finite size and shape anisotropy effects on the magnetization reversal. An anomaly was found in the upper branch of the hysteresis loops, probably caused by incomplete bias in the patterned structures. The asymmetry in magnetization reversal mechanism commonly found in the two branches of the hysteresis loops of unpatterned Co/CoO layers is altered in the patterned structures, consistent with the existence of interfacial domains.

Fe(x)/Ag(2.6 nm) multilayer heterostructures containing Fe layers of periodically altered thickness have been prepared by molecular beam evaporation to study the influence of ferromagnetic layers on the magnetic properties of granular multilayers. The magnetic properties were examined by SQUID magnetization measurements and Mossbauer spectroscopy, and the magnetoresistance was measured in parallel and transversal magnetic fields up to 12 T. Samples with x=0.2 and 1.5 nm were prepared both as separated and as interleaved multilayer heterostructures. The average blocking temperature of the granular Fe layers (x=0.2 nm) is not altered when the thickness of every fourth layer is increased to 1.5 nm. On the other hand the temperature dependence of the magnetoresistance was found to be significantly different for the separated and the interleaved samples. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Polarized neutron reflectometry with neutron spin analysis is used to investigate the magnetic properties of large arrays of ferromagnetic rectangular Co bars with in-plane magnetization, as well as exchange-biased Co/CoO islands. The off-specular neutron scattering signal contains satellite peaks due to the lateral periodicity of the dot array. Using polarized neutrons, the intensity of the satellite peaks is measured as a function of an external magnetic field applied in the sample plane. Spin analysis of the scattered neutrons reveals the magnetization reversal and saturation within the bars.

Fe films with thickness varying from 46 to 1750 A have been deposited on oxidized Si substrates coated with a Ag buffer layer. The surface morphology of both the Ag buffer layer and the Fe films was investigated by atomic force microscopy. Analysis of the images shows that the surface roughness of the Fe layers is completely dominated by the surface roughness of the Ag buffer layer. Magnetization measurements revealed that the magnetic properties of the Fe films are strongly affected by the surface roughness. The change in the coercivity as a function of the film thickness depends on the ratio of the film thickness and the typical size of the height variations of the surface. When this ratio is smaller than 1, the coercivity increases with increasing film thickness. For a ratio larger than 1, the coercivity decreases monotonically with the film thickness.

The electronic structure of silver–palladium heterostructures is investigated, both experimentally and through ab-initio simulations. Synchrotron-induced photoelectron spectroscopy characterisations of the work function and the valence band structure are compared to and explained by simulations of slab and bulk heterostructures. Work functions and equilibrium geometries are shown to be in agreement with XPS, XRD, and STM measurements, and confirm in particular the pseudomorphic growth of Ag on Pd. Further insight into the differing behavior of the two terminating metal surfaces is extracted from the simulations.

We report on the use of specular and off-specular polarized neutron reflectometry (PNR) for the study of magnetization reversal in patterned magnetic structures. We discuss the instrumental requirements and the measurement method and illustrate its potential by applying it to lithographically structured trilayer systems of the form (7.5 nm Au/20 nm Co/7.5 nm Au) prepared on oxidized Si wafers. In order to study the influence of the shape of the structures on the magnetic properties we prepared rectangular bars with a width of 1 μm and a length of 4 μm. The dots were arranged in a square lattice symmetry with a period of 10 μm. By using a two-dimensional position sensitive detector (PSD) we were able to record not only the specularly but also the off-specularly scattered intensity which has maxima at particular angles due to the in-plane periodicity of the discs. The second system that we studied is that of wires with a width of 2 μm and a period of 15 μm consisting of an exchange biased Co/CoO bilayer structure. By applying neutron spin analysis and monitoring the neutron reflectivity at a fixed angle of incidence as a function of an external magnetic field we were able to effectively study the magnetization reversal process in both systems.

We demonstrate how room temperature scanning Hall probe microscopy (SHPM) can be applied to noninvasively probe the (meta-)stable magnetic domain states of individual mesoscopic Co bars as a function of applied field. These data are correlated with magneto-optical measurements of the hysteresis loop as well as higher spatial resolution magnetic force microscopy imaging. In particular, we show how a combination of visualization techniques is essential for fully understanding the mechanism of magnetization reversal in such microstructures. Micromagnetic calculations of the magnetic states and their corresponding stray fields are correlated with the observations. These experiments prove the usefulness of a noninvasive and quantitative technique such as room temperature SHPM in an applied magnetic field to study magnetic domain stability and switching field distributions.

We have investigated the magnetic and superconducting properties of a nanostructured ferromagnet/superconductor hybrid system, consisting of a Co layer with a square array of rectangular holes (antidots), covered with a thin continuous (nonperforated) superconducting Pb layer. The Co film with an antidot lattice shows a strong in-plane magnetic shape anisotropy determined by the array configuration and the rectangular shape of the antidots. Remanent domain structures in the uncovered Co antidot array are imaged at room temperature by magnetic force microscopy. The superconducting pinning properties of the hybrid ferromagnet/superconductor system are studied for different magnetic states of the Co antidot lattice. We demonstrate that the contribution to the superconducting pinning potential caused by the stray field from the domain walls is stronger than that arising from the periodic modulation due to the underlying antidot lattice.We have investigated the magnetic and superconducting properties of a nanostructured ferromagnet/superconductor hybrid system, consisting of a Co layer with a square array of rectangular holes (antidots), covered with a thin continuous (nonperforated) superconducting Pb layer. The Co film with an antidot lattice shows a strong in-plane magnetic shape anisotropy determined by the array configuration and the rectangular shape of the antidots. Remanent domain structures in the uncovered Co antidot array are imaged at room temperature by magnetic force microscopy. The superconducting pinning properties of the hybrid ferromagnet/superconductor system are studied for different magnetic states of the Co antidot lattice. We demonstrate that the contribution to the superconducting pinning potential caused by the stray field from the domain walls is stronger than that arising from the periodic modulation due to the underlying antidot lattice.

We demonstrate the possibility to reliably image vortices in superconducting Nb films with a low-temperature magnetic-force microscope. Our force microscope enables to monitor the surface topography as well, allowing to correlate the location of the vortices with specific topographic features. For Nb films of different thickness (32 nm − 87 nm) and different Tc (7.9 K − 9.1 K) we studied how the vortex configuration changes when changing the applied magnetic field under field-cooled conditions (1 mT − 5 mT). We find that the vortex pinning preferentially occurs in between the grains appearing at the film surface. This is consistent with a distribution of pinning centers which is governed by the columnar growth of the Nb films. For thicker Nb films the vortex arrangement is no longer dominated by pinning alone, and there appear short-range correlations in the vortex lattice. The short-range correlations are enhanced when increasing the applied magnetic field.

We have studied the magnetic and superconducting properties of a nanostructured magnetic/superconducting hybrid system, consisting of a Co layer with a square array of rectangular antidots, covered with a thin 500 A superconducting Pb layer. The magnetic force microscopy data have revealed that the domain walls are located between neighbouring antidots and are pinned at the antidot corners. The superconducting pinning properties of the hybrid system are studied by means of SQUID magnetisation measurements for different magnetic states of the Co antidot lattice. The results show that the stray field, coming from the domain walls in the antidot array, contributes more to the pinning potential than the periodic modulation of the underlying Co layer. The flux lines seem to be pinned at the domain walls between the antidots. In this way, possible matching effects are lost. The network of domain walls thus creates a new type of an artificial pinning array.

We succeeded to image with magnetic force microscopy individual vortices in thin Nb films as well as in thin YBa 2 Cu 3 O 7− δ (YBCO) films. Relying on the imaging of microfabricated gold loops, we are able to identify the exact location of the vortices within 10 nm with respect to topographic features. The center of most of the vortices is located in between the grains appearing at the film surface. For the Nb films with a larger coherence length, the pinning can be linked to the reduced film thickness in between the protruding grains. For the YBCO films with a very small coherence length, the pinning is likely to be dominated by line defects at the trenches in between the growth islands. On the other hand, Fourier analysis of the imaged vortex distribution shows that for thicker Nb films not all of the vortices are pinned in between the grains. Due to the vortex–vortex repulsion, the vortex lattice reveals short-range correlations which become more pronounced at higher fields.

This paper gives an overview of pinning phenomena in superconductors with artificial magnetic pinning arrays. Different ferromagnetic structures have been considered in combination with a low Tc type-II superconducting film. Magnetic force microscopy is used to characterise the magnetic patterns. The pinning properties (critical current, matching effects) are investigated by macroscopic measurements (SQUID, electrical transport) as well as by local observation using scanning Hall probe microscopy. It is shown that, besides structural and geometric modulations, the magnetic interaction of flux lines (FLs) with the ferromagnetic patterns plays an essential role in their pinning properties. The local magnetic stray field affects the order parameter and determines the pinning through the magnetic interaction with the flux lines. To understand this interaction, one should take into account fluxoid quantisation effects and the possibility of having additional induced flux quanta in the superconductor. The magnetic moments of the dots and their mutual alignment with the applied magnetic field are especially important for the asymmetric pinning by perpendicularly magnetised dot- and antidot arrays.

We investigated the pinning of flux lines in a superconducting film by a regular array of magnetic antidots. The sample consists of a Co/Pt multilayer with perpendicular magnetic anisotropy in which a regular pattern of submicron holes is introduced and which is covered by a type-II superconducting Pb film. The resulting ferromagnetic/superconducting heterostructure shows a pronounced asymmetric magnetization curve with respect to the field polarity. This asymmetry clearly demonstrates that the magnetic contribution dominates the pinning potential imposed by the magnetic antidots on the superconducting film., Comment: 7 pages, 6 figures, including erratum with 1 page, 1 figure

We have performed magnetic force microscopy measurements on isolated 35 nm thick rectangular Co structures. The structures have a length L ranging between 0.25 and 10 μm and a width W ranging between 0.25 and 5.5 μm, covering aspect ratios m=L/W between 1 and 40. This enables us to map the transition from a magnetic single-domain state towards a magnetic multidomain state when increasing the size of the structures. This transition depends on the size as well as the aspect ratio of the structures. Our results can be interpreted in terms of the theoretical model developed by A. Aharoni [J. Appl. Phys. 63, 5879 (1988)].

A Cr(001)/Fe(001) superlattice with ten bilayers grown by molecular beam epitaxy on a Ag(001) substrate is studied by in situ scanning tunneling microscopy (STM) and ex situ x-ray diffraction (XRD). Layer-resolved roughness parameters determined from STM images taken in various stages of the superlattice fabrication are compared with average values reported in the literature or obtained from the fits of our XRD data. Good agreement is found for the rms roughnesses describing vertical roughness and for the lateral correlation lengths characterizing correlated as well as uncorrelated interface roughness if peculiarities of STM and XRD are taken into account. We discuss in detail (i) the possible differences between the STM topography of a free surface and the morphology of a subsequently formed interface, (ii) contributions due to chemical intermixing at the interfaces, (iii) the comparison of XRD parameters averaged over all interfaces versus layer-resolved STM parameters, and (iv) the question of the coherent field of view for the determination of rms values. (C) 2001 American Institute of Physics.

We have investigated the structure and regularity of macroscopically large arrays of submicron magnetic Au/Co/Au dots, which were prepared by combining electron beam lithography, molecular beam epitaxy, and lift-off techniques. Atomic force microscopy was used to characterize the surface roughness of the dots and to show the reproducibility of dot size and periodicity over large areas; low-angle x-ray diffuse scattering experiments were employed to construct a mapping of the reciprocal space in the vicinity of the (000) reflection of the dots. The reciprocal space mapping thus provides information about the internal structure of the dots, as well as about the lateral periodicity of the dot array. This work underlines the important complementarity of scanning probe and x-ray diffraction techniques for the detailed characterization of patterned structures. We observed that the x-ray diffraction patterns are extremely sensitive to the orientation of the dot lattice with respect to the incoming x-ray beam, allowing a quantitative analysis of the lateral periodicity of the dot array and the size of the individual dots.

The differential microwave absorption method of shortened waveguide and the differential and direct d.c. measurements were applied to the study of the field dependence of electric resistivity of Fe/Cr epitaxially grown multilayers, exhibiting antiferromagnetic coupling between the adjacent Fe layers. The experimental results of all methods obtained at static magnetic field intensities up to 30 kG and at frequencies up to 70 GHz are in a good mutual agreement, the advantages and drawbacks of the individual methods are discussed. The results confirm well the applicability of microwave methods for contactless studies of the GMR effect.

We have studied the superconducting properties of antidot arrays and mesoscopic antidot clusters near the superconducting-normal phase boundary. Characteristic minima and maxima have been observed in the magnetore-sistance, critical current and phase boundary caused by the formation of stable vortex configurations at the antidots. A comparison with a simple theoretical model has shown that the effects in the arrays as well as in the clusters originate from quantization of the fluxoid at the antidots. This model has enabled an identification of all vortex configurations.

We report on the effect of Pt on the growth kinetics of δ-Ni 2Si and Ni1-xPtxSi thin films formed by solid phase reaction of a Ni(Pt) alloyed thin film on Si(100). The study was performed by real-time Rutherford backscattering spectrometry examining the silicide growth rates for initial Pt concentrations of 0, 1, 3, 7, and 10 at. relative to the Ni content. Pt was found to exert a drastic effect on the growth kinetics of both phases. δ-Ni2Si growth is slowed down tremendously, which results in the simultaneous growth of this phase with Ni 1-xPtxSi. Activation energies extracted for the Ni 1-xPtxSi growth process exhibit an increase from E a 1.35 ± 0.06 eV for binary NiSi to Ea 2.7 ± 0.2 eV for Ni1-xPtxSi with an initial Pt concentration of 3 at. . Further increasing the Pt content to 10 at. merely increases the activation energy for Ni1-xPtxSi growth to Ea 3.1 ± 0.5 eV. © 2013 AIP Publishing LLC. ispartof: Journal of Applied Physics vol:113 issue:16 status: published

Using the influence of surface roughness on the coercivity of thin magnetic films, we have produced an artificially modulated magnetic domain configuration in a chemically homogeneous polycrystalline thin magnetic film. This is achieved by evaporating a thin Fe film on top of a smooth substrate that was previously covered with an array of considerably rougher Ag lines. Magneto-optical Kerr effect measurements revealed the presence of two distinct switching fields in the hysteresis loops. In the intermediate state, a stable magnetic domain configuration of antiparallel aligned domains is achieved. Magnetic force microscopy images indicate that interacting cross-tie domain walls are separating the magnetic domains.

We have measured the off-specular polarized neutron reflectivity of a regular array of rectangular magnetic polycrystalline Co dots, which were prepared by a combination of electron-beam lithography, molecular beam deposition, and lift-off processes. The dots have a length-to-width ratio of 4:1 imposing a strong shape anisotropy. The intensity of the off-specular satellite reflection was monitored as a function of the magnetic field applied parallel to the rows of dots and in the plane of the sample, allowing us to analyze the magnetization-reversal process using the four spin-polarized cross sections.

We succeeded in studying the magnetization-reversal process of a large array of in-plane-magnetized ferromagnetic Co disks by using off-specular polarized neutron reflectometry with spin analysis. We observed enhanced intensity in the off-specular scattered intensity at particular angles. The positions of these satellites are correlated to the lateral periodicity of the magnetic disks. The magnetization-reversal process of the dot array could be effectively studied by measuring the magnetic field dependence of the spin-flip and non-spin-flip contributions to the off-specular intensity of the satellites. The measured spin-flip intensities clearly show that the magnetization reversal is dominated by domain-wall movement within the Co dots and not by a uniform rotation of single-domain particles nor by the presence of a vortex-domain state.

We report on the redistribution of Sn during Ni germanide formation on Ge1– x Sn x /〈Ge(100)〉 and its influence on the thin film growth and properties. These results show that the reaction involves the formation of Ni5Ge3 and NiGe. Sn redistributes homogenously in both phases, in which the Sn/Ge ratio retains the ratio of the as-deposited Ge1– x Sn x film. Sn continues to diffuse after full NiGe formation and segregates in two regions: (1) at the interface between the germanide and Ge1– x Sn x and (2) at the surface, which has major implications for the thin film and contact properties.

Large positive magnetoresistance (LPMR) effects have been measured at temperatures T

Nb/Cu multilayers grown by molecular beam epitaxy have been studied by x‐ray diffraction and atomic force microscopy. X‐ray diffraction provides the average interface roughness while atomic force microscopy shows the roughness and topology of the upper surface. Comparison of both methods shows that high‐angle diffraction averages over a lateral length which is in good agreement with the typical grain size.

Heteroepitaxial CoxNi1−xSi2 layers with good crystalline quality (χmin=3.5%) have been formed by ion beam synthesis. For a sample with x=0.66, we found that this ternary silicide layer contains 11% type B and 89% type A orientation. The transmission electron microscopy investigation reveals that the type B component is mainly located at the interfaces and with a thickness of only a few monolayers. X‐ray diffraction studies of the sample show that the strain of the type B component is smaller than that of the type A and is probably the reason for such a unique distribution of the type B component in the epilayer. Rutherford backscattering‐channeling, Auger electron spectroscopy, transmission electron microscopy, and x‐ray diffraction have been used in this study.

The training effect for exchange bias in field-cooled Co/CoO bilayers films is investigated. Previous experiments on the same system have shown that, starting from the ascending branch of the first hysteresis loop, coherent magnetization rotation is the dominant reversal mechanism. This is confirmed by the performed numerical simulations, which also indicate that the training is predominantly caused by changes of the rotatable anisotropy parameters of uncompensated spins at the Co/CoO interface. Moreover, in contrast with what is commonly assumed, the exchange coupling between the rotatable spins and the ferromagnetic layer is stronger than the coupling between the ferromagnet and the spins responsible for the bias. Thus, uncompensated spins strongly coupled to the ferromagnet contribute to the coercivity rather than to the bias, whatever the strength of their magnetic anisotropy. © 2014 AIP Publishing LLC. ispartof: JOURNAL OF APPLIED PHYSICS vol:115 issue:24 pages:1-6 status: published

The low-temperature magnetic behavior of granular Co-CoO exchange bias systems, prepared by oxygen ion implantation in Co thin films and subsequent annealing, is addressed. The thermal activation effects lead to an O migration which results in virtually pure Co areas embedded in a structurally relaxed and nearly stoichiometric CoO phase. This yields decreased training and exchange bias shifts, while the blocking temperature significantly increases, coming close to the N'eel temperature of bulk CoO for samples implanted to a fluence above 1 x 1017 ions/cm² (15% O). The dependence of the exchange bias shift on the pristine O-implanted content is analogous to that of the antiferromagnetic thickness in most ferromagnetic/antiferromagnetic systems (i.e., an increase in the exchange bias shift up to a maximum followed by a decrease until a steady state is reached), suggesting that, after annealing, the enriched Co areas might be rather similar in size for samples implanted above 1 x 1017 ions/cm², whereas the corresponding CoO counterparts become enlarged with pristine O content (i.e., effect of the antiferromagnet size). This study demonstrates that the magnetic properties of granular Co-CoO systems can be tailored by controllably modifying the local microstructure through annealing treatments.

The lattice site location of radioactive 27 Mg implanted in AlN was determined by means of emission channeling. The majority of the 27 Mg was found to substitute for Al, yet significant fractions (up to 33%) were also identified close to the octahedral interstitial site. The activation energy for interstitial Mg diffusion is estimated to be between 1.1 eV and 1.7 eV. Substitutional Mg is shown to occupy ideal Al sites within a 0.1 Å experimental uncertainty. We discuss the absence of significant displacements from ideal Al sites, in the context of the current debate, on Mg doped nitride semiconductors. © 2013 AIP Publishing LLC. ispartof: Applied Physics Letters vol:103 issue:26 status: published