Search

In the current study, we developed a simple and biocompatible method for producing core–shell nanoparticles (NPs). Citrate auto combustion and green procedures were used to create core–shell Ag/CoGd0.025Er0.05Fe1.925O4 (Ag/CGEFO) sample with an average crystallite size of 26.84 nm. The prepared samples were characterized via different structural techniques, such as x-ray diffraction (XRD), Raman Spectroscopy (RS), High-Resolution Transmission Electron Microscopy, and Energy Dispersive x-ray analysis. These analyses were utilized to characterize and confirm the successful formation of the core–shell architecture. For core–shell NPs, all peaks of Ag and CGEFO ferrite are detected in the XRD, confirming the co-presence of the ferrite spinel phase and the cubic Ag phase. The magnetic hysteresis curves demonstrate typical hard ferri-magnetic behavior along with maximum magnetic saturation values up to 53.74 emu g−1 for the CGEFO sample, while an enhanced coercivity is detected for the coated sample. Moreover, the width of the hysteresis loop is increased for the Ag/CGEFO sample compared to the uncoated one. This indicates that the addition of Ag as a shell increases magneto crystalline anisotropy. Moreover, the E g of uncoated CGEFO is equal to 1.4 eV, increasing to 3.6 eV for coated ones. This implies the influence of CGEFO is diminished when the surface is coated with Ag (shell), and the reflectance of the Ag/CGEFO core–shell is nearly dependent on the reflectance of the Ag shell layer. Consequently, the Ag/CGEFO can be used as a light shielding substance. [ABSTRACT FROM AUTHOR]

The magnetic characteristics of Fe-based nanocrystalline alloys can be influenced by temperature. The conventional dynamic Jiles–Atherton (J-A) hysteresis model does not take into consideration the impact that temperature has on magnetic characteristics. A novel variable-temperature dynamic J-A hysteresis model is proposed in this paper to effectively address the issue. Firstly, the hysteresis loops of Fe-based nanocrystalline are measured at −50 °C–130 °C and DC state. The five parameters of the J-A hysteresis model are identified at various temperatures using the particle swarm optimization algorithm, and five parameters are fitted as functions of temperature. Subsequently, the five parameters as functions of temperature are introduced into the conventional dynamic J-A hysteresis model to construct a novel variable-temperature dynamic J-A hysteresis model, which can not only reflect the impact of temperature but also accurately calculate the losses. Finally, hysteresis loops and losses of Fe-based nanocrystalline alloy are simulated and calculated at different temperatures and frequencies by the variable-temperature dynamic J-A hysteresis model. Meanwhile, this paper also investigates the trends and percentages of hysteresis loss, excess loss as well as eddy current loss with frequency and temperature. Compared to the results of measured data, the maximum average error of the variable-temperature dynamic J-A hysteresis model is 5.83%. [ABSTRACT FROM AUTHOR]

Magnetic textures in the self-supported nanostructure, such as vortex, are promising for magnetic hyperthermia therapy and spintronics due to their low remanent state and topological protection. These configurations emerge from energy minimization in confined systems, such as nanodisk or nanoparticles. There are many techniques used to confine these magnetic textures. However, the most robust, cheap, and reproducible is always sought. This work applies colloidal lithography to produce self-supported nanocaps with a vortex as the ground state. Firstly, we perform micromagnetic simulations to determine which diameters and thicknesses stabilize the vortex as a ground state on nanocaps. Secondly, we simulate the magnetization curves to find the conditions with the smallest remanent state and largest loop hysteresis curves area. Finally, we experimentally corroborate the vortex configuration ground state using electron holography and vibrating the sample magnetometer. In addition, we performed a dynamic simulation to investigate the gyrotropic modes of the vortex core. We present a concise route to the fabrication of scalable vortex magnetic nanocaps. Our results show that the magnetic nanocaps produced have a great potential for application in medicine, such as magnetic hyperthermia, and in spintronics, for spin-transfer torque nano-oscillators. [ABSTRACT FROM AUTHOR]

We report the results, from experimental and micromagnetic studies, of the magnetic normal modes in artificial square spin ice systems consisting of ferromagnetic-monodomain islands. Spin-wave properties are measured by Brillouin light scattering. The mode spectra contain several branches whose frequencies are sensitive to the magnitude and in-plane orientation of an applied magnetic field. We also identify soft modes that exhibit different behaviours depending on the direction of the applied magnetic field. The obtained results are well described with micromagnetic simulations of independent magnetic elements arranged along two sublattices.

The present report leads to the development of a lead-free perovskite system (Ba Ca)(Sn0.11Zr0.05Ti0.84)O3 (BCSZTx); 0 0.20, exhibiting relaxor ferroelectric behaviour in an average cubic structure. The x-ray diffraction measurements have shown a simple cubic phase with Pm m space group for all the compositions. Despite having a centrosymmetric cubic phase, a slim hysteresis loop has been observed via PE loop measurements. Raman spectroscopic measurements have revealed the presence of local ordering in the macroscopic cubic matrix, corresponding to 'A' and 'B' sites. The cooperative behaviour of 'A' and 'B' site off-centered (local) atoms leading to microscopic polar symmetry in the macroscopically cubic matrix is held responsible for the observed relaxor ferroelectric nature. Owing to the aforementioned contrapositive behaviour, these ceramics have exhibited a high value of dielectric constant. Eventually, we have clearly observed a decisive role of Ca2+ dopant at 'A' site in BCSZTx ceramic system leading to the enhancement in the relaxor ferroelectric behaviour and dielectric properties. The presence of a slim hysteresis loop along with broad and diffuse dielectric nature makes these ceramics, a potential candidate for energy storage applications. [ABSTRACT FROM AUTHOR]

From the last decade, the development of a generic model for memristive systems which simulates the biologically inspired nervous system of living beings, is one of the most attracting aspects. More specifically, the develop generic model has capability to resolve the problems in the field of artificial neural network. Here, a generic, non-linear analytical memristive model, which is based on interfacial switching mechanism, has been discussed. The proposed model has the capability to simulate the high-density neural network of biological synapses that regulates the communication efficacy among neurons and can implement the learning capability of the neurons. Further, the proposed model is the parallel connection of the rectifier and memristor which shows better non-linear profile along with non-ideal effects and rectifying nature in its pinched hysteresis loop in the resistive switching characteristics. Moreover, proposed model shows the significant low value of maximum error deviation ∼4.44% for Y2O3-based and ∼4.5% for WO3-based memristive systems, respectively in its neuromorphic characteristics with respect to the corresponding experimental results. Therefore, the proposed analytical memristive model can be utilized to develop the memristive system for real-world applications based on neuromorphic behaviors of any transition metal oxide-based memristive systems. [ABSTRACT FROM AUTHOR]

We conducted a thorough experimental and numerical study of the micromagnetic properties of Permalloy (Ni80Fe20) microdisks exhibiting target domain structures at remanence. Vortex configurations are quite common in such microdisks and correspond to an in-plane (IP) flux closure configuration of cylindrical symmetry with an out-of-plane (OOP) magnetized core. In contrast, target domain configuration are observed in thicker microdisks and are characterized by a vortex configuration of the IP component of the magnetization superposed to an OOP component of magnetization which oscillates as a function of the distance to the microdisk center resulting in the formation of concentric domains. The ratio of the OOP oscillatory component of the magnetization to the IP vortex one increases with the thickness of the microdisk. Hysteresis loops were measured under IP and OOP field. The results at remanence and under magnetic field could be interpreted by micromagnetic simulations in which the microdisks were described as an assembly of partially coupled columns representing the granular nanostructure of the films from which the microdisks were patterned. Quite original magnetization processes take place in these microdisks exhibiting target domain remanent configuration. These include in particular entire flipping of the domain configuration and annihilation/creation of ring domains. [ABSTRACT FROM AUTHOR]

In the present work, the microstructure evolution and macro-response of a ferromagnetic shape memory alloy under stimuli of magnetic fields with different frequency and coupled magnetic-mechanical loading are investigated via a real-space phase field simulation. It is found that the coercive field is reduced from 0.724 to 0.423 with the magnetic frequency f decrease from Hz to Hz, wherein the concomitant domain wall motion and magnetization rotation are captured as well. Moreover, simulation results demonstrate that, under the coupled magnetic-mechanical loading, the coercive field of the magnetic hysteresis loop could be reduced by applying a compressive strain perpendicular to the magnetic field direction. The domain evolution is mainly divided into three types during the coupled magnetic-mechanical loading, namely (a) domain wall motion with the magnetization rotation, (b) pure magnetization rotation, and (c) 180° domain coordinated domain switching. To better understand the domain evolution, we propose an index , with and indicating the absolute value of the averaged magnetization component and over the whole studied system, to characterize the magnetization change during the microstructure evolution. [ABSTRACT FROM AUTHOR]

The structural phase transformation in a non-stoichiometric shape memory Fe42.8Mn27.6Ga29.6 Heusler glass-coated microwire was experimentally observed using indirect magnetic, permeability, and electrical resistance measurements. While the temperature dependence of magnetization revealed hysteresis of magnetization during the heating and cooling process, magnetic hysteresis loops point to the change in the direction of the easy magnetization axis of the low- and high-temperature phase. Additionally, the unusual behavior of the permeability and electrical resistance measurements are in good agreement with the magnetic measurements. The x-ray diffraction profile measured at room temperature revealed the coexistence of a high-temperature L21 phase (a = 5.88 Ă...) and low-temperature phase with the L12 structure (a = 3.71 Ă...) and can be considered as another proof of the shape memory effect that is expected in the Feâ€"Mnâ€"Ga-based Heusler alloys. In the presented glass-coated microwire, it is not only possible to shift the transformation temperature with the external magnetic field, but from its initial permeability value, it is possible to determine whether the alloy has undergone the structural transformation. Therefore, the presented Feâ€"Mnâ€"Ga-based glass-coated microwire may be considered a suitable candidate for microactuators with sensory capabilities. [ABSTRACT FROM AUTHOR]

Vanadium dioxide (VO2)-based microactuators with fast and highly efficient dynamic responses have become one of the best candidates for microrobots and micromuscles. VO2 microstructures fabricated by rolling nanomembranes with component gradient along the vertical direction are considered to be promising for future applications, and thus need further investigation. Here, we quantify the effects of substrate temperature on the initial internal stress of the nanomembranes and achieve rolled-up single-component VO2 nanomembranes via stress engineering. Through synchrotron radiation x-ray diffraction (XRD) measurements, we find that the stress of nanomembranes is negatively correlated with substrate temperature, and its exact value can be calculated from the shift of the XRD peaks. Moreover, experimental results demonstrate that VO2 nanomembranes deposited on a Si/SiO2 substrate possess lower phase transition temperature and narrower hysteresis loops than those grown on quartz and Al2O3 substrates with similar surface morphology. The upward bending of the VO2 nanomembrane due to the tensile stress gradient from temperature changing during deposition is demonstrated, and the rolled-up VO2 microstructures with tunable stress and narrow hysteresis loops are considered to have advantageous applications in microactuators. [ABSTRACT FROM AUTHOR]

Transparent and epitaxial 0.95(K0.49Na0.49Li0.02)(Ta0.2Nb0.8)O3-0.05CaZrO3 with 2 wt.% MnO2 addition (KNNLT-CZM) lead-free ferroelectric film heterostructures are fabricated on the La0.07Ba0.93SnO3 (LBSO)-coated SrTiO3 (001) substrates using pulsed laser deposition. The optical measurements show that these film heterostructures exhibit good transmittance with a maximum transmittance of ∼80%. Temperature-dependent dielectric properties demonstrate that the KNNLT-CZM films possess a high Curie temperature (TC) above 420 °C, and exhibit an orthorhombic to tetragonal phase transition at ∼170 °C. Furthermore, these film heterostructures also have a large twice remnant polarization of 29.66 μC cm−2 and well-defined ferroelectric hysteresis loops up to 200 °C. The x-ray photoelectron spectra suggest that partial K elements did not enter in the lattice of the KNNLT-CZM perovskite structure and the Mn dominantly existed in the form of Mn2+. The observed good transmittance, high TC and excellent electrical properties of the LBSO-buffered KNNLT-CZM film heterostructures indicate that these films have great application potential in opto-electronic devices and film transistors. [ABSTRACT FROM AUTHOR]

In the present work, a unique case for the stabilization of the antiferroelectric phase in NaNbO3 has been presented, where the desired results were obtained in spite of it defying the set pattern predicted by researchers to date for achieving similar results. Antiferroelectric phase stabilization of NaNbO3 was achieved with doping of 1% CdTiO3, which is much lower compared to other dopants reported earlier. From the Rietveld refinement of x-ray diffraction (XRD) patterns, structural changes with respect to octahedral tilting were found to be responsible for the increase in energy barrier required for stabilizing antiferroelectric P over ferroelectric Q phase in (1-x)NaNbO3-xCdTiO3 ceramics. Temperature-dependent dielectric properties implied a shift in Curie temperature with an increase in CdTiO3 concentration. P-E hysteresis loop measurement demonstrated a square-shaped ferroelectric loop for NaNbO3 ceramic, while the antiferroelectric double hysteresis loop was observed for composition x = 0.01 and x = 0.02. The results were verified by observing characteristic superlattice peaks in the XRD patterns. [ABSTRACT FROM AUTHOR]

This article reports exchange bias (EB) in nanocrystalline cobalt chromite CoCr2O4, - a phenomenon manifested by loop shift followed by increase in coercivity after cooling the sample in static magnetic field. The average particle size of the nanocrystalline CoCr2O4 is 30 nm, confirmed from transmission electron microscopy images. Thermal variation of magnetization data M(T), in zero field cooling (ZFC) and field cooling (FC) modes depict long range order below the lock-in transition at TL≈16 K, spin-spiral transition at TS≈28 K and a collinear ferrimagnetic state at TC≈100 K. Magnetic hysteresis loops are recorded in ZFC and FC modes at different cooling fields (). In addition, hysteresis loops are recorded in FC mode for a wide temperature range. In both cases, a clear signature of conventional exchange bias effect is observed. Analysis of the training effect in magnetic hysteresis loop and temperature dependent ac susceptibility (χac) at different frequencies suggest that the surface spins of CoCr2O4 nanoparticles play an important role in controlling the magnetic properties, and enhance the EB effect in collaboration with competition between non-collinear spiral spin state and collinear long range ferrimagnetic order. [ABSTRACT FROM AUTHOR]

To promote the development of NaNbO3-based antiferroelectrics, it is necessary to stabilize the antiferroelectric phase over ferroelectric phase through compositional design strategy. In this work, Bi(Mg2/3Nb1/3)O3 was doped into NaNbO3 for decreasing the Goldschmidt tolerance factor, and double P-E hysteresis loop was observed. Raman spectra showed the enhanced antiferroelectricity in Bi(Mg2/3Nb1/3)O3 doped samples, and 1/6(100) rather than the usually reported 1/4(100) diffraction spots were observed from selected area electron diffraction patterns. This work is helpful in promoting the research of NaNbO3-based antiferroelectric systems. [ABSTRACT FROM AUTHOR]

This article reports exchange bias (EB) in nanocrystalline cobalt chromite CoCr2O4, - a phenomenon manifested by loop shift followed by increase in coercivity after cooling the sample in static magnetic field. The average particle size of the nanocrystalline CoCr2O4 is 30 nm, confirmed from transmission electron microscopy images. Thermal variation of magnetization data M(T), in zero field cooling (ZFC) and field cooling (FC) modes depict long range order below the lock-in transition at TL≈16 K, spin-spiral transition at TS≈28 K and a collinear ferrimagnetic state at TC≈100 K. Magnetic hysteresis loops are recorded in ZFC and FC modes at different cooling fields (). In addition, hysteresis loops are recorded in FC mode for a wide temperature range. In both cases, a clear signature of conventional exchange bias effect is observed. Analysis of the training effect in magnetic hysteresis loop and temperature dependent ac susceptibility (χac) at different frequencies suggest that the surface spins of CoCr2O4 nanoparticles play an important role in controlling the magnetic properties, and enhance the EB effect in collaboration with competition between non-collinear spiral spin state and collinear long range ferrimagnetic order. [ABSTRACT FROM AUTHOR]

Novel lead-free (1−x)Ba0.90Sr0.10Ti0.90Zr0.10O3–(x)BiYb0.9Sc0.1O3 (0 ≤ x ≤ 0.10) relaxor ceramic solid solutions were prepared by modified mechano-chemical activation technique with the aim of improving the energy storage properties. The Rietveld analysis of the materials indicated that all the samples show a tetragonal crystal structure with a perovskite phase. The grain morphology and density of the materials have significantly improved with BiYb0.9Sc0.1O3 (BYS) substitution. The dielectric study indicates a gradual transformation from classical to relaxor dielectric with increasing BYS substitution. The ferroelectric to paraelectric transition temperature increases with increasing BYS concentration and has shown a rise of approximately 24 °C for the sample with x = 0.10 compared to the bare sample (x = 0.0). Further, the ferroelectric hysteresis loops have become significantly slimmer with a slight increase in saturation polarization, which indicates an improvement in energy storage performance of the material with BYS substitution. The optimum energy storage properties have been obtained at x = 0.06, and the sample showed a high recoverable energy density of 1.24 J cm−3 under the applied electric field of ±100 kV cm−1. The electric field-induced bipolar strain is improved by 12% for the sample with concentration x = 0.06 compared to the bare sample. This study provides a basis for preparing BaTiO3 based high performance ferroelectric ceramics with their potential application in pulse capacitors. [ABSTRACT FROM AUTHOR]

Magnetic properties, domain morphology and magnetization reversal processes were investigated for two sets of [Pt/Co(x)]N multilayers with various (Co/Pt) bilayer repeat numbers (N) and Co layer thicknesses (x) using hysteresis loops, magnetic force microscopy (MFM), and the first-order reversal curve method. When N ranges from 7 to 20, the effective anisotropy, Keff, of the multilayers increases from 0.86 × 106 erg cc−1 to 1.48 × 106 erg cc−1 and the coercivity (Hc) is maintained at approximately 290 Oe. Moreover, when x increases, Keff drops from 0.52 × 106 erg cc−1 to 0.09 × 106 erg cc−1 and Hc decreases from 285 Oe to 75 Oe. According to the switching field distribution, evidence has been found that the magnetization switching is gradually dominated by the reversible process and the portion of the irreversible switching process declines from 86% to 40% and 58% to 10% when N and x are increased, respectively. [ABSTRACT FROM AUTHOR]

This study is aimed at the preparation of silica-coated nanoparticles of cobalt–zinc ferrite and their heating properties with respect to potential application in magnetic fluid hyperthermia. The magnetic cores of Co0.4Zn0.6Fe2O4+γ possessing two different sizes were prepared by the coprecipitation method followed by annealing and mechanical treatment. The subsequent encapsulation of the samples by silica led to colloidally stable suspensions in water. The single phase character of the cores was confirmed by x-ray powder diffraction while detailed studies of the coated products by transmission electron microscopy and x-ray photoelectron spectroscopy showed that the silica shell had a thickness of at least 5 nm. The dc magnetic measurements were employed in order to determine the concentrations of magnetic particles in suspensions and to analyse the distribution of blocking temperatures. The heating efficiency of the nanoparticles was studied simultaneously by means of magnetic and calorimetric measurements in various ac fields. Specifically, the magnetic losses were calculated from the ac hysteresis loops while the heating effect of the nanoparticles was determined by measuring the time dependence of the temperature of their suspensions. The evaluation of the heating power from the latter experiments was supplemented by deriving the corrections for non-adiabatic properties of the calorimeter. More accurate results enabled detailed analysis and comparison with data published for other heating agents. [ABSTRACT FROM AUTHOR]

Memristive devices are triggering innovations in the fields of nonvolatile memory, digital logic, analogue circuits, neuromorphic engineering, and so on. Creating new memristive devices with unique characteristics would be significant for these emergent applications. Here we report the coexistence of nonvolatility and volatility in Pt/Nb-doped SrTiO3 (NSTO)/In memristive devices. The Pt/NSTO interface contributes a nonvolatile resistive switching behaviour, whereas the NSTO/In interface displays a volatile hysteresis loop. Combining the two interfaces in the Pt/NSTO/In devices leads to the unique coexistence of nonvolatility and volatility. The results imply more opportunities to invent new memristive devices by engineering both interfaces in metal/insulator/metal structures. [ABSTRACT FROM AUTHOR]

Magnetic multilayers consisting of itinerant ferromagnetic SrRuO3 (SRO) and antiferromagnetic NiO were pulse-laser deposited on (0 0 1) SrTiO3 substrates. After small-field cooling, enhancements from both the unconventional exchange bias (EB) and the large coercive field were observed in the multilayers. Coercivity values for the in-plane hysteresis loop increased by almost 50 times in comparison with a pure SRO film. The maximum value of the bias moment in the minor loop and the EB field can be achieved in different cooling fields. Moreover, hysteresis indicates a two-step magnetization reversal. We speculate that a pinned layer exists at the SRO/NiO interface producing magnetic regions that pin the ferromagnetic SRO layer. [ABSTRACT FROM AUTHOR]

We report the effects of thickness of spacer layers and temperature on the magnetic properties of multilayer structured [FeTaC(50 nm)/Ta(x nm)]n=3/FeTaC(50 nm)/substrate amorphous thin films. A transcritical loop with a large coercivity (HC) of 25 Oe was observed for x = 0 film, but the loop shape was changed to flat loop along with a rapid decrease in HC (<0.25 Oe) by introducing Ta spacer layers. This is attributed to loss of perpendicular anisotropy causing a transition from stripe domain structure to in-plane orientation of spins. Magnetic hysteresis loops measured at different temperatures exhibited a spacer layers' thickness dependent multistep magnetization reversal processes for temperature below 80 K. Thermo- magnetization curves obtained under zero-field-cooled and field-cooled conditions displayed a bifurcation between them for x = 0 film. However, the bifurcation point was shifted to lower temperatures with increasing x and disappeared eventually for films with x ⩾ 4. High-temperature magnetization data revealed no significant changes in the magnetic properties up to Curie temperature. The observed results are elucidated on the basis of change in magnetic structure with the thickness of the spacer layers, pinhole effects at the interface, and temperature, instigating an effective reduction in perpendicular anisotropy and magnetic disorder, and thereby enhancing magnetic properties in multilayer thin films. [ABSTRACT FROM AUTHOR]

(Bi3.15Nd0.85)(Ti2Fe0.5Co0.5)O12−δ ceramics were prepared by the conventional solid-state reaction method. The sample of the layered perovskite phase was successfully obtained. The measurement of x-ray photoelectron spectroscopy indicated the coexistence of Fe3+ and Fe2+ ions. The multiferroic behaviour of the sample at room temperature (RT) was demonstrated by the ferroelectric (2Pr = 8 µC cm−2, 2Ec = 64 kV cm−1 at applied electric field 86 kV cm−1) and ferromagnetic (2Mr = 32 m emu g−1, 2Hc = 872 Oe at applied magnetic field 1.1 T) hysteresis loops. Remarkably, a clearly identified positive magnetocapacitance effect was observed with a large magnetocapacitance value of ∼14.2% at 30 kHz. Comparison of the impedance Cole–Cole plots measured with and without magnetic field revealed that the occurrence of magnetocapacitance effect is accompanied by an increase in the conductivity under magnetic field, which is explained by the enhancement of electron jumping in Fe2+–O–Fe3+ chains by magnetic field. The present results suggest a new candidate for a RT multiferroic material with large magnetocapacitance effect. [ABSTRACT FROM AUTHOR]

Epitaxial 120 nm La0.7Sr0.3MnO3 (LSMO) compressively strained thin films were deposited on single-crystalline SrLaAlO3(001) (SLAO) substrates by the pulsed laser deposition (PLD) method. From the x-ray diffraction study, we confirmed that the c-axis of the LSMO crystal pointed out of the film plane. Two kinds of magnetic experiments were performed on the film: (i) the in-plane (field H ≣HP) and the out-of-plane (field H ≣HN) magnetic hysteresis loop measurements and (ii) magnetic force microscopy scans. We have proved from both theory and experiment that the LSMO film should exhibit the weak and tilted perpendicular magnetic anisotropy at room temperature (RT), that is, the easy axis (EA) is tilted relative to the film normal by an angle Θo ≒ 37°, when the film is in the demagnetized state. The magnetic domain (MD) structure of the demagnetized LSMO film showed a maze-like pattern. Although from the in-plane hysteresis loop, HP = 600 Oe seems large enough to saturate the film, the corresponding MD structure was not in a single-domain state. Instead, there were two types of MDs: the canted MD and the saturated MD. The MD patterns of the LSMO film between the demagnetized and the remanent states were different. In addition, there were double-switch phenomena in the out-of-plane hysteresis loop. When |HN| ≅140 Oe, a transition of the MD pattern from the maze-like to the closure (or dense-stripe) type occurred. [ABSTRACT FROM AUTHOR]

We report the magnetic properties of c- and m-plane GaN :Gd films grown on different substrate materials. Additionally, we have investigated the magnetic behaviour of the bare substrates in order to analyse their possible contribution on the properties of this material system. For the growth of c-phase GaN :Gd we have used 6H-SiC(0 0 0 1) and GaN/Al2O3 templates. Whereas templates only exhibit a diamagnetic behaviour, the SiC substrates show clear signatures of ferromagnetism at room temperature. Rutherford backscattering spectroscopy and secondary ions mass spectrometry have revealed traces of Fe in the SiC substrates. This Fe contamination seems to be related to the ferromagnetic ordering observed in these substrates. LiAlO2(0 0 1) is a good choice for growth of m-plane diluted nitrides due to its diamagnetic behaviour. The hysteresis loops of c- and m-phase GaN :Gd deposited on template and LiAlO2, respectively, show coercivity and magnetic saturation. These characteristics together with the magnetization curves are indications of an intrinsic ferromagnetic behaviour in the GaN : Gd. [ABSTRACT FROM AUTHOR]

Time-dependent magnetic behaviour at room temperature is investigated in highly oriented epitaxial hard magnetic thin films. Single-layer films with nominal composition PrCo5 and PrCo7 were studied, along with two SmCo55/Fe/SmCo5trilayer films, with Fe layer thicknesses of 11 and 16 nm. The films were prepared using pulsed laser deposition on Cr buffered MgO (110) substrates. For the trilayer system, judicious choice of the thickness of the hard (SmCo5) and soft (Fe) magnetic layers results in an exchange-coupled two-phase magnet. All the thin films exhibit switching behaviour, i.e. a near square hysteresis loop, and the details of this behaviour are explored through both measurement of the hysteresis loop, at very slow field sweep rates, and the irreversible susceptibility, χirr . Measurements of the sweep rate dependence of the intrinsic coercivity, and magnetic viscosity on the major hysteresis loop were performed. For each film, three techniques were used to determine the fluctuation field, Hf : from the sweep rate data; from the magnetization relaxation data using the waiting time method; and from S/χirr , where S is the magnetic viscosity coefficient. Differences in the value of Hf determined using the three different techniques, and the equivalence of the three techniques, are discussed. Further insights into the time-dependent behaviour of the magnetization are gained from observations of the spontaneous remagnetization, following dc demagnetization. The study shows the thin films to be of high-stability. Furthermore, it supports the view that magnetization reversal in these materials is most likely an incoherent process, and not a process involving the uniform reversal of a grain. The model of weak pinning provides a useful framework for understanding magnetization processes. [ABSTRACT FROM AUTHOR]

Based on Landau-Ginzburg phenomenological theory, a first-order ferroelectric bilayer or superlattice with an antiferroelectric interface coupling has been studied by taking into account the spatial variation of polarization within each constituent film and the surface effect. The hysteresis loops are obtained and the size effect of a bilayer is discussed. The loop patterns vary between typically antiferroelectric and typically ferroelectric depending on the thickness ratio, the coupling constant, the thickness and the extrapolation length. The antiferroelectric coupling has a great effect on the phase transition of a bilayer. It is shown that the size-driven phase transition cannot be observed in a ferroelectric bilayer in the case of strong antiferroelectric coupling. [ABSTRACT FROM AUTHOR]

This paper reports nanoscale piezoelectric measurements on ferroelectric poly(vinylidene fluoride-co-trifluoroethylene) (P(VDF-TrFE)) films prepared by the Langmuir-Blodgett (LB) technique. Polarization patterning, piezoelectric hysteresis and relaxation after poling are studied in this work by piezoresponse force microscopy. High quality P(VDF-TrFE) films with a copolymer content of 30% were fabricated using a Schaefer monolayer transfer setup permitting precise control of the film microstructure. The thickness of the films deposited with 100 transfers was ?64?nm. Local switching resulted in written polarization lines with the lateral size in the range 70-300?nm depending on polarization time. Local hysteresis loop (at a fixed tip position) demonstrated clear ferroelectric switching with the coercive voltage 8-10?V that corresponds to a macroscopic switching field (?1.5?MV?cm?1) at a?10?nm depth below the tip. Relatively slow ageing after poling was observed with the characteristic relaxation time of about 1500-2000?s depending on the polarization direction. The obtained results demonstrate that the stable polarization patterns can be created in LB P(VDF-TrFE) films and attest them as suitable candidates for memory and nanotemplate applications. [ABSTRACT FROM AUTHOR]

The nonvolatile memory characteristics of metal-oxide-semiconductor (MOS) structures containing Au nanocrystals in the Al2O3/SiO2 matrix were studied. In this work, we have demonstrated that the use of Al2O3 as control oxide prepared by atomic-layer-deposition enhances the erase speed of the MOS capacitors. A giant capacitance-voltage hysteresis loop and a very short erase time which is lower than 1 ms can be obtained. Compared with the conventional floating-gate electrically erasable programmable read-only memories, the erase speed was promoted drastically. In addition, very low leakage current and large turn-around voltage resulting from electrons or holes stored in the Au nanocrystals were found in the current-voltage relation of the MOS capacitors. [ABSTRACT FROM AUTHOR]

The effect on the polarization of antiferroelectric (AFE) PNZST ((Pb,Nb)(Zr,Sn,Ti)O3) thin films by e-E (dc bias field) cycles was studied. It was shown that in these films the AFE ordering is destroyed by the application of a dc electrical field bias along the surface normal direction. After removing the dc bias the film relaxes slowly back to the initial AFE state. This phenomenon is dependent on the film thickness. The relaxation time decreases with increasing film thickness. With increasing storage time of the sample after removing the dc bias at room temperature or heat treatment above the Curie temperature, the AFE ordering can return. From the characteristics of hysteresis loops and e-E behaviours, we can ascertain that this phenomenon could be attributed to the difference in the poled volume at the interfaces between the electrode and the film. [ABSTRACT FROM AUTHOR]

Longitudinal electrostrictive strains in an as-sintered and two annealed (0.4)Pb(In1/2Nb1/2)O3?:?(0.6)Pb(Mg1/3Nb2/3)O3relaxor ceramics were measured by laser-interferometry. The field-related electrostriction coefficients (M33) of the ceramics were then determined. The electrostrictive coefficients progressively decreased with annealing and the strain responses became nonlinear. The ferroelectric hysteresis loops of the as-sintered and annealed ceramics showed progressive decrease in coercive fields and maximum polarizations with increasing annealing time. Transmission electron microscopy studies revealed enlargement of 1?:?1 B-site ordered domains with annealing. The changes in the high-field responses of the annealed ceramics are interpreted as arising from a higher degree of long-range order caused by annealing. A field-induced mechanism is proposed to explain the correlation between the B-site cation long-range order and the electrostrictive behaviour in this relaxor. [ABSTRACT FROM AUTHOR]

Polycrystalline Fe3O4/Al bilayers with Al underlayers (ULs) of different thicknesses were fabricated using facing-target reactive sputtering. Structure analyses revealed that Al ULs improve the crystallinity and reduce the thickness of the Fe3O4amorphous initial layer. Room-temperature magnetization of the Fe3O4films with 30?nm thick Al ULs is ?450?emu?cm?3at 50?kOe fields, which is much larger than that of the polycrystalline Fe3O4monolayer deposited under the same conditions. The field-cooled hysteresis loop of Fe3O4films on the 30?nm thick Al layer shows a 50?Oe exchange bias field at 5?K, much smaller than 256?Oe detected in polycrystalline Fe3O4monolayer and the exchange bias fields in the samples with and without 30?nm Al UL decrease with the increasing temperature. The enhancement of the magnetization and the sharp decrease in the exchange bias field observed in the Fe3O4films with Al ULs can be attributed to the decoupling of the antiferromagnetic domains and the thickness reduction of the amorphous Fe-O layers between the polycrystalline Fe3O4films and the Al ULs. [ABSTRACT FROM AUTHOR]

The frequency and temperature dependences of the hysteresis loops in Pb[(Zr0.52Ti0.48)0.95(Mn1/3Nb2/3)0.05]O3 ceramics have been investigated. The polarization-field hysteresis curves show ‘pinched’ shapes at room temperature and higher frequencies, whereas they display normal square-like loops at 200°C and frequencies lower than 10 mHz. Critical ferroelectric features such as the coercive field, polarization and internal bias field show a strong frequency or temperature dependence. The close relations between the P–E loops and the applied frequency and temperature indicate that the defect dipolar moment may change its magnitude with variation of the frequency or temperature. Comparing with the intrinsic depinning procedure induced by the changes in the distribution of defect dipoles, we provide new evidence for an extrinsic depinning mechanism of the defect dipoles in the bulk ceramics. [ABSTRACT FROM AUTHOR]

High-energy electron-irradiated poly(vinylidene fluoride–trifluoroethylene) 56/44 mol% copolymers are studied in a broad dose ranging from 0 to 110 Mrad. The experimental results are obtained by differential scanning calorimetry (DSC), x-ray diffraction, dielectric constant, dc conductivity and polarization hysteresis loop based on structural changes and dielectric relaxation behaviour. All the x-ray and DSC results show that both the crystalline and polar ordering decreased after irradiation, indicating a partial recovery from trans–gauche bonds to local trans bonds (polar ordering). The dielectric relaxation peaks, obeying the Vogel–Fulcher Law, indicate that the copolymers have transformed from a normal ferroelectric to a relaxor ferroelectric. It is also found that dc conductivity can be modulated with electron irradiation, as well as the hysteresis loop characteristics. [ABSTRACT FROM AUTHOR]

Here, we reported the structure, morphology and multiferroic properties of the La0.67Ca0.33MnO3/Ba0.85Ca0.15Zr0.9Ti0.1O3 (LCMO/BCZT) magnetoelectric epitaxial heterostructure deposited on (1 0 0) MgO single crystal substrate using pulsed laser deposition. XRD RSM confirmed the epitaxial growth of the heterostructure with single oriented grains, and the smooth surface and uniform film growth of the heterostructure were revealed by the AFM analysis. The heterostructure exhibited multiferroic properties with a dielectric constant of 378, a remnant polarization of 10.26 µC cm−2, a maximum piezoelectric coefficient of 62.5 pm V−1 and a saturated magnetization 814.8 emu cm−3. The well-shaped ferroelectric and ferromagnetic hysteresis loops verified the multiferroic nature of the heterostructure with a maximum magnetoelectric coefficient αE31 of 36.9 mV (cm · Oe)−1. [ABSTRACT FROM AUTHOR]

Fe65.9Cr11.6Si7.5B15 amorphous wire was annealed at 520°C for 30 min and pre-magnetized with a positive field of 60 kA m-1. Its quasi-saturated hysteresis M(H) loop, longitudinal susceptibility, χL, and circular susceptibility, χc, as a function of axial static field, H, were measured. We found the M(H) loop shifted 89 A m-1 in the negative field direction and both χL(H) and χc(H) exhibited asymmetric distribution with respect to H = 0: χL(H > 0) < χL(H < 0), χc(H > 0) > χc(H < 0). The displaced hysteresis loop and the asymmetric χL(H) can be explained by the magnetostatic interaction between hard magnetic inclusions and the residual soft matrix, while the asymmetric χc(H) is supposed to the different micro-domains structures resulting from this interaction. [ABSTRACT FROM AUTHOR]

We report the formation and the role of defect dipoles in Fe doped Pb(Zr0.52Ti0.48)O3 (PZT) epitaxial thin film grown on SRO/LSAT substrate by pulsed laser deposition. The observed enhancement of spontaneous polarization in Nb-doped PZT thin film is found to be due to easy orientation and mobility of domain walls. The presence of defect complexes in Fe doped PZT film is responsible for the voltage offset or asymmetric polarization versus electric field hysteresis loop. Topography and nanoscale polarization switching of pure and doped PZT films are investigated by piezo force microscopy. X-ray photoelectron spectroscopy (XPS) study is used to confirm the presence of defect dipoles in Fe-doped PZT thin film. Detailed analysis of the XPS spectra also revealed that the defect dipoles are only formed in the Fe doped system and is absent in Nb- modified PZT thin film. [ABSTRACT FROM AUTHOR]

The double-shifted magnetic hysteresis loops, which are accompanied by the formation of bi-domain state, are normally observed after zero field cooling a demagnetized sample or as-deposited ferromagnetic (FM)/antiferromagnetic (AFM) structures. In the pioneer works, this phenomenon was explained by the imprinting of ferromagnetic FM domain in AFM layer, however the interaction between the FM and AFM domain has never been discussed. In this work, we observed double-shifted magnetic hysteresis loops and bi-domain state in [Co 0.3/Ni 0.4i]N/IrMn multilayers with perpendicualr magnetic anisotropy. By comparing the domain patterns in (Co 0.3/Ni 0.4)N/IrMn multilayers, we may conclude that the bi-domain state in FM/AFM structure is related to both the FM and AFM domain, and the domain size is determined by the minimum of the total energy in the FM/AFM system through the interficial coupling. [ABSTRACT FROM AUTHOR]

An ideal memristor is defined as a resistor with memory that, when subjected to a time-dependent current, , its resistance RM(q) depends only on the charge q that has flowed through it, so that its voltage response is . It has been argued that a clear fingerprint of these ideal memristors is a pinched hysteresis loop in their I– curves. However, a pinched I– hysteresis loop is not a definitive test of whether a resistor with memory is truly an ideal memristor because such a property is shared also by other resistors whose memory depends on additional internal state variables, other than the charge. Here, we introduce a very simple and unambiguous test that can be utilized to check experimentally if a resistor with memory is indeed an ideal memristor. Our test is based on the duality property of a capacitor-memristor circuit whereby, for any initial resistance states of the memristor and any form of the applied voltage, the final state of an ideal memristor must be identical to its initial state, if the capacitor charge finally returns to its initial value. In actual experiments, a sufficiently wide range of voltage amplitudes and initial states are enough to perform the test. The proposed test can help resolve some long-standing controversies still existing in the literature about whether an ideal memristor does actually exist or it is a purely mathematical concept. [ABSTRACT FROM AUTHOR]

Experimentally hysteresis loop shifts have been widely observed in antiferromagnetic (AF) nanoparticles. Here numerical investigations show that this effect is dependent on the angle between the easy axis of the AF spins and the applied magnetic field in uncompensated nanoparticles. In contrast, the loop shifts disappear in compensated nanoparticles. The results suggest that the uncompensated spins and field directions are essential ingredients to generate loop shifts in AF nanoparticle systems. The present study hints at a possible way to optimize the magnetic performance of AF nanostructures. [ABSTRACT FROM AUTHOR]

We report here on the enormously large value of the spontaneous exchange bias (SEB) of ~5.1 kOe in the Sm1.5Ca0.5CoMnO6 bulk double perovskite system after zero-field cooling from an unmagnetized state. Depending on the path used for measuring the magnetic hysteresis loop, P-type or N-type, the EB field varies significantly. Dc and ac magnetization reveals a super-spin-glass-like (SSG) state below 19 K. The EB effect has been observed below the glassy transition temperature. The conventional exchange bias (CEB) as well as the SEB increase with a decrease in temperature and show monotonic variation. All these interesting features can be explained through the multimagnetic phase of double perovskite and the onset of unidirectional anisotropy driven by interface exchange coupling between the SSG, turned isothermally into a field-induced superferromagnetic shell and antiferromagnetic core. [ABSTRACT FROM AUTHOR]

MnBi:FeCo hard-soft bilayers are investigated using micromagnetic simulations with open boundary conditions and two-dimensional (2D) periodic boundary conditions (PBC). Open and PBC yield similar coercivities of about 1.01 T, in agreement with experiment, but the hysteresis-loop shape is very different in the two theoretical approaches. The difference is ascribed to edge effects, which occur in open boundary conditions but not in PBC and experiment. Near the nucleation field, a curling or vortex mode develops in dots with circular cross sections. The curling mode, which is caused by magnetostatic self-interaction, does not negatively affect the high coercivity of 1.01 T. The magnetostatic self-interaction contributes to the favorable second-quadrant behavior of the MnBi:FeCo thin films. [ABSTRACT FROM AUTHOR]

We have investigated the magnetic behavior of Fe1 − xGax (15 ≤ x ≤ 22 at.%) thin films grown by electrodeposition. The samples exhibit a <1 1 0 > texture although a rather small diffraction peak related to the (1 0 0) phase can also be observed. The layers do not present perpendicular magnetic anisotropy but magnetic hysteresis loops and magnetic force microscopy evidence a significant out-of-plane component for the magnetization. This component seems to increase for Ga contents around the 19 at.% value at which these alloys present a peak for the magnetostriction constant in the [1 0 0] direction. In this composition range, we have also observed an enhancement of the period of the magnetic structures. The experimental results indicate that the origin of the domain configuration is the presence of clusters with a (1 0 0) structural phase. The out-of-plane component of the magnetization seems to arise because of the compression of these nanoaggregates. [ABSTRACT FROM AUTHOR]

The nonlinear dependence of the dielectric permittivity on electric field ε(E) is modeled by the relationship ε(E) = ε00 + 1/(α + βEeff2), where Eeff = E + κP(E). Using an appropriate mathematical representation of the polarization loop P(E), it is possible to describe correctly the hysteretic behavior of the curve ε(E). This model allows the separation of the intrinsic and extrinsic contributions to the dielectric response from the experimental measurement of ε(E). The model is validated for PZT and PLZT ferroelectric thin films. It is shown that the polarization hysteresis loop can be reconstructed from the curve ε(E), which can be very useful for separating polarization current from leakage current in ferroelectric samples. [ABSTRACT FROM AUTHOR]

Exchange bias properties of [FeNi/IrMn]n multilayer films with variable thickness of the ferromagnetic layers and different repetitions n were determined by using static and dynamic measurement techniques. The static magnetic properties were revealed through magnetometry measurements at room temperature following major hysteresis loops and first-order reversal curves protocols. Room temperature x-band ferromagnetic resonance (FMR) and vector network analyser (VNA)-FMR experiments were used to determine dynamically the exchange anisotropy in the FeNi/IrMn multilayers. From the static measurements the exchange anisotropy was determined while dynamic measurements allowed the determination of additional parameters including anisotropy field, saturation magnetization and rotatable anisotropy. The differences between the values of the exchange biased obtained from each technique are discussed. [ABSTRACT FROM AUTHOR]

We have investigated the structural, optical and ferromagnetic properties of undoped and Fe-doped TiO2 nanoribbons (NRbs) grown by a solvothermal method. A strong room temperature ferromagnetism (RTFM) is observed in both undoped and Fe-doped TiO2 NRbs. Fe-doped TiO2 NRbs exhibited a ∼4.8-fold enhancement in RTFM as compared to the undoped NRbs grown under similar conditions. However, the RTFM decreases at higher Fe concentration, possibly due to antiferromagnetic ordering between nearby Fe3+ ions caused by a super exchange interaction. X-ray diffraction patterns reveal the pure TiO2(B) phase, the TiO2(B)–anatase mixed phase and the anatase–rutile mixed phase of the TiO2 structure. Field emission scanning electron microscopy and transmission electron microscopy observations reveal NRbs with uniform pore distribution and nanopits formed on the surface for both undoped and Fe-doped NRbs. These samples exhibit strong visible photoluminescence associated with oxygen vacancies and the ferromagnetic hysteresis loop, both of which are strongly enhanced after vacuum annealing. Optical absorption, electron spin resonance and x-ray photoelectron spectroscopic analyses are performed to elucidate the origin of RTFM. The observed RTFM in undoped and Fe-doped TiO2 NRbs is qualitatively explained through a model involving bound magnetic polarons, which include an electron locally trapped by an oxygen vacancy with the trapped electron occupying an orbital overlapping with the unpaired electron (3d1) of a Ti3+ ion and/or the unpaired electron (3d5) of a Fe3+ ion. The development of TiO2 NRbs with tunable optical and magnetic properties constitutes an important step towards realizing improved magneto-optical and spintronic devices from novel TiO2 nanostructures. [ABSTRACT FROM AUTHOR]

The effects of sputter-deposition-induced and post-deposition thermally activated layer intermixing on the exchange bias properties of [Pt/Co]x3/Pt(tPt)/IrMn films with out-of-plane anisotropy and deposited under a perpendicular magnetic field are investigated. The consequences of the intermixing on the magnetic properties are correlated with atom probe structural investigations. We observe that Co–Mn and Co–Pt intermixing are already present in the as-deposited state. The intermixing is more pronounced for Pt on Co (∼50%) than for Mn on Co (∼10%). It is observed that annealing up to 200 °C does not result in noticeable further diffusion of Mn in Co. In contrast, it significantly accentuates the Co–Pt initial intermixing. This enhanced intermixing leads to a 40% reduction in the exchange bias field. We measured that this reduction is not primarily due to changes in effective anisotropy or in saturation magnetization. This is possibly ascribed to a decrease in the mean interfacial moment and exchange stiffness both due to the observed reduction in Co content within the Co sublayers. [ABSTRACT FROM AUTHOR]

The influence of an applied compressive stress on the hysteresis curve and domain structure in conventional (1 1 0) [0 0 1] Fe–3%Si steel cut transverse to the rolling direction is studied. Quasistatic hysteresis loops under compressive stress up to 75 MPa were measured. The magnetic domains and magnetization processes were observed by longitudinal Kerr microscopy at different levels of stress. It is shown that the bulk hysteresis loop can be described with a good accuracy by the action of an effective field, which is the product of the stress and a function of magnetization. Domain observations have shown that the reasons for the effective field are demagnetizing fields due to the disappearance of supplementary domains along [0 1 0] and [1 0 0] at low fields and different domain systems in different grains at moderate fields. The latter are caused by differences in grain sensitivity to stress depending on the degree of misorientation. A decrease in the effective field above 1 T is connected with a transformation of all grains into the same domain system—the column pattern. [ABSTRACT FROM AUTHOR]

Phase transition behaviour of La-modified sodium bismuth titanate ceramics [(Na0.5Bi0.5)1[?]1.5xV0.5xLax]TiO3 (NBLT) was investigated. The two anomalies in er(T) and DSC analysis indicated that lower temperature phase transitions below 200 degC became pronounced with La additions. The polarization relaxation of er(T) and double hysteresis loops showed that the intermediate region between two dielectric anomalies was the antiferroelectric modulated phase. The origin of the modulated antiferroelectric state was discussed in terms of disordering effects of the La ions and cation vacancies. With increasing La content, the long-range symmetry of the dipoles in the ferroelectric phase was disturbed in the intermediate region. The competition between rhombohedral ferroelectric phase and tetragonal paraelectric phase contributed to the formation of a modulated antiferroelectric phase in NBLT ceramics. [ABSTRACT FROM AUTHOR]

We report a method to predict the frequency dependence of coercive fields in ferroelectric films. The deduction of this method as well as the analysis are based on investigations of intrinsic switching kinetics of high-quality, single-crystal-like, epitaxial Pb(Zr0.2Ti0.8)O3 thin films with extended defect-free structures. The newly suggested relationship, i.e. an exponential decrease in frequency with the reciprocal of the coercive field, differs from the empirical power-law relationship. The proposed equation relates the coercive field (Ec) measured using ferroelectric hysteresis loops to the activation fields determined from pulse width switching measurements, which provides a way to understand the behaviour of Ec as a function of frequency from the switching kinetics point of view. [ABSTRACT FROM AUTHOR]

We report the ferroelectric and pyroelectric properties of the composite films of lithium tantalate (LT) nanoparticle in poly(vinylidene fluoride) PVDF matrix at different volume fractions of LT (fLT = 0.047, 0.09 and 0.17). For an applied electric field of 150 kV cm[?]1 the nonvolatile polarization of the composite was observed to increase from 0.014 uC cm[?]2 at fLT = 0 to 2.06 uC cm[?]2 at fLT = 0.17. For fLT = 0.17, the composite films exhibit a saturated ferroelectric hysteresis loop with a remanent polarization (2Pr = 4.13 uC cm[?]2). Compared with pure poled PVDF the composite films also showed a factor of about five enhancement in the pyroelectric coefficient at fLT = 0.17. When used in energy detection mode the pyroelectric voltage sensitivity of the composite films was found to increase from 3.93 to 18.5 V J[?]1 with an increase in fLT from 0.0 to 0.17. [ABSTRACT FROM AUTHOR]