Investigate Magnetization Reversal Research Articles

Surface Spin Polarization in the Magnetic Response of GeTe Rashba Ferroelectric

We experimentally investigate magnetization reversal curves for a GeTe topological semimetal. In addition to the known lattice diamagnetic response, we observe narrow magnetization loop in low fields, which should not be expected for non-magnetic material. The diamagnetic hysteresis loop is unusual, so the saturation level is negative in positive fields, and the loop is passed clockwise, in contrast to standard ferromagnetic behavior. We show, that the experimental hysteresis curves cannot be obtained from standard ferromagnetic ones by adding/subtracting of any linear dependence, or even by considering several interacting magnetic phases. The latter possibility is also eliminated by the remanence plots technique (Henkel or \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\delta M$$\\end{document} plots). We explain our results as a direct consequence of the correlation between ferroelectricity and spin-polarized surface states in GeTe, similarly to magnetoelectric structures.

Magnetization reversal properties and magnetostatic interactions of disk to rod-shaped FeNi layers separated by ultra-thin Cu layers

From fast magnetic memories with low-power consumption to recording media with high densities, realizing the magnetization reversal and interaction of magnetic layers would allow for manipulating the ultimate properties. Here, we use a pulsed electrochemical deposition technique in porous alumina templates (50 nm in pore diameter) to fabricate arrays of nanowires, consisting of FeNi layers (26−227 nm in thickness) with disk to rod-shaped morphologies separated by ultra-thin (3 nm) Cu layers. By acquiring hysteresis curves and first-order reversal curves (FORCs) of the multilayer nanowire arrays, we comprehensively investigate magnetization reversal properties and magnetostatic interactions of the layers at different field angles (0° ≤ θ ≤ 90°). These involve the extraction of several parameters, including hysteresis curve coercivity (H c Hyst ), FORC coercivity (H c FORC ), interaction field distribution width (ΔH u ), and irreversible fraction of magnetization (IF m ) as a function of θ. We find relatively constant and continuously decreasing trends of H c Hyst when 0° ≤ θ ≤ 45°, and 45° < θ ≤ 90°, respectively. Meanwhile, angular dependence of H c FORC and IF m shows continuously increasing and decreasing trends, irrespective of the FeNi layer morphology. Our FORC results indicate the magnetization reversal properties of the FeNi/Cu nanowires are accompanied with vortex domain wall and single vortex modes, especially at high field angles. The rod-shaped layers also induce maximum ΔH u during the reversal process, owing to enhancements in both magnetizing and demagnetizing-type magnetostatic interactions.

Magnetization reversal of (Sm, Ce)2(Co, Fe, Cu, Zr)17 magnets as per soft x-ray magnetic circular dichroism microscopy

We investigated magnetization reversal of (Sm, Ce)2(Co, Fe, Cu, Zr)17 magnets as per x-ray magnetic circular dichroism microscopy. Magnetization reversal initially occurs at the ferromagnetic grain boundaries or in the vicinity of nonmagnetic Sm oxides. As the demagnetization field increases after magnetization reversal, the reversal region extends into the grain from these areas by the magnetic domain wall motion. Energy-dispersive x-ray analysis using an electron probe micro-analyzer shows that, at the grain boundaries, the Fe concentration is higher and the Cu concentration is lower compared to that inside of the grains; and concentrations of Sm, Co, Fe, and Cu vary in the vicinity of Sm oxides. By measuring the Co L3 absorption intensity, we verified that local coercivities in these areas are very low compared to those inside of the grain. These results imply that the magnetization reversal that occurs in these areas is induced by the variation in the composition. The results obtained in our research will be useful for improving the magnetic properties of Sm–Co magnets.

Magnetization reversal, damping properties and magnetic anisotropy of L1-ordered FeNi thin films

L 1 0 -ordered magnetic alloys such as FePt, FePd, CoPt, and FeNi are well known for their large magnetocrystalline anisotropy. Among these, the L10-FeNi alloy is an economically viable material for magnetic recording media because it does not contain rare earth and noble elements. In this work, L10-FeNi films with three different strengths of anisotropy were fabricated by varying the deposition process in a molecular beam epitaxy system. We have investigated magnetization reversal along with domain imaging via a magneto-optic Kerr effect based microscope. It is found that in all three samples, the magnetization reversal happens via domain wall motion. Furthermore, ferromagnetic resonance spectroscopy was performed to evaluate the damping constant (α) and magnetic anisotropy. It was observed that the FeNi sample with a moderate strength of anisotropy exhibits a low value of α∼4.9×10−3. In addition to this, it was found that the films possess a mixture of cubic and uniaxial anisotropies.

Micromagnetic simulation of thickness-dependent magnetization reversal processes in elongated iron nanodots

Micromagnetic simulations were used to investigate magnetization reversal processes in elongated ferromagnetic nanodots, prepared by combining two half-circles with a rectangle. The micromagnetic simulation program OOMMF is based on dynamically solving the Landau-Lifshitz-Gilbert equation of motion. Material parameters were chosen as typical for Fe (iron). Lateral dimensions were in most simulations chosen as 730 nm x 133 nm, while the dot height was varied between 3 nm and 54 nm. For different in-plane angles of the external magnetic field, varying magnetization reversal processes were found with changing dot thickness, offering a possibility to tailor magnetic states by modifying the thickness of the nanodot.

Current-induced synchronized magnetization reversal of two-body Stoner particles with dipolar interaction**Project supported by the National Natural Science Foundation of China (Grant No. 11274236) and the Deutsche Forschungsgemeinschaft via SFB 689.

We investigate magnetization reversal of two-body uniaxial Stoner particles, by injecting spin-polarized current through a spin-valve structure. The two-body Stoner particles perform synchronized dynamics and can act as an information bit in computer technology. In the presence of magnetic dipole–dipole interaction (DDI) between the two particles, the critical switching current Ic for reversing the two dipoles is analytically obtained and numerically verified in two typical geometric configurations. The Ic bifurcates at a critical DDI strength, where Ic can decrease to about 70% of the usual value without DDI. Moreover, we also numerically investigate the magnetic hysteresis loop, magnetization self-precession, reversal time and synchronization stability phase diagram for the two-body system in the synchronized dynamics regime.

Large area asymmetric ferromagnetic nanoring arrays fabricated by capillary force lithography

In this study, we have investigated the nanofabrication of asymmetric ferromagnetic ring arrays by capillary force lithography, which incorporates the essential feature of nanoimprint lithography. The capillary lithography technique enables the fabrication of large area magnetic nanostructures and makes it possible to systematically control the shape of magnetic nanostructures. We prepared various ferromagnetic Co ring arrays with various ring widths down to 100 nm. We investigated magnetization reversal of ferromagnetic nanoring arrays using the focused magneto-optical Kerr effects (FMOKE) and micromagnetic simulation. It was found that magnetization reversal could be controlled by varying the width and asymmetry in ferromagnetic nanoring structures.

Magnetization reversal assisted by the inverse piezoelectric effect in Co-Fe-B/ferroelectric multilayers

We investigate magnetization reversal assisted by electric fields in a Co${}_{40}$Fe${}_{40}$B${}_{20}/$Co$/$Pd multilayer with soft perpendicular anisotropy deposited onto an epitaxial piezoelectric layer. Both the nucleation and depinning magnetic fields show a strong reduction of up to 30$%$ under the application of an electric field. These results show good prospects for assisting the switching processes in ultra-low-power spintronic devices.

Zero-field magnetization reversal of two-body Stoner particles with dipolar interaction

We investigate magnetization reversal in a system of two Stoner particles with uniaxial anisotropies both subject to a static and antiparallel magnetic field, and taking into account their mutual dipolar interaction. We identify an interesting regime of stable synchronized magnetic dynamics where the two particles are implementing a single information bit. Here a modified Stoner-Wohlfarth limit occurs which results in a dramatically lower critical switching field Hc (including Hc=0) and also a substantially shorter reversal time. Our analytical results are verified by numerical simulations and offer new technological perspectives regarding devices for information storage and/or fast magnetic response.

Phase diagram of magnetization reversal processes in nanorings

We investigate magnetization reversal processes of magnetic nanorings. Exploring extensive parameter sets using Monte Carlo technique combined with scaling method, we constructed magnetization switching phase diagrams for such structures. The dominant switching mechanisms are found to strongly depend on the relative spatial dimensions of the rings, i.e., height, width, and radius. Furthermore, they are shown to depend on a characteristic exchange length scale, which is determined by the competing short-range ferromagnetic and long-range dipolar interactions in these systems. Detailed simulations allow us to identify three switching mechanisms, which should be useful for building high-density storage systems.

Magnetization reversal in amorphous Fe/Dy multilayers: A Monte Carlo study

The Monte Carlo method in the canonical ensemble is used to investigate magnetization reversal in multilayers of amorphous transition metal and rare earth elements. Our study is based on a model containing diluted clusters which exhibit an effective uniaxial anisotropy in competition with random magnetic anisotropy in the matrix. We simulate hysteresis loops for an abrupt profile and a diffuse one obtained from atom probe tomography analyses. Our results give evidence that the atom probe tomography profile favors perpendicular magnetic anisotropy in agreement with magnetic measurements. Moreover, the hysteresis loops calculated at several temperatures qualitatively agree with the experimental ones.

Magnetization Reversal of Exchange-biased Bilayers and Trilayers Probed using Front and Back LT-MOKE

Magneto-optical Kerr effect (MOKE) magnetometry was used to investigate magnetization reversal dynamics in 30-nm NiFe/15-nm FeMn, 15-nm FeMn/30-nm CoFe bilayers, and 30-nm NiFe/(2,10)-nm FeMn/30-nm CoFe trilayers. The in-plane magnetization components of each ferromagnetic layer, both parallel and perpendicular to the applied field, were separately determined by measuring the longitudinal and transverse MOKE hysteresis loops from both the front and back sides of the film for an oblique incident s-polarized beam. The magnetization of the FeMn/CoFe bilayer was reversed abruptly and symmetrically through nucleation and domain wall propagation, while that of the NiFe/FeMn bilayer was reversed asymmetrically with a dominant rotation. In the NiFe/FeMn/CoFe trilayers, the magnetic reversal of the two ferromagnetic layers proceeded via nucleation and domain wall propagation for 2-nm FeMn, but via asymmetric rotation for 10-nm FeMn. The exchange-biased ferromagnetic layers showed the magnetization reversal along the same path in the film plane for the decreasing and increasing field branches from transverse MOKE hysteresis loops, which can be qualitatively explained by the theoretical model of the exchange-biased ferromagnetic/antiferromagnetic systems.

Magnetization reversal and interlayer coupling in Co50Fe50 nanomagnets

We investigated magnetization reversal mechanism in elliptical shaped nanomagnets made from single layer and pseudospin valve Co50Fe50 films. The structures were fabricated using deep ultraviolet lithography and the lift-off process. We observed that the magnetization reversal process of the single layer elements is strongly dependent on the film thickness. For thickness tCoFe=10 nm, the magnetization reversal process is dominated by a systematic coherent rotation, whereas for tCoFe=60 nm, the reversal process is mediated by vortex nucleation, displacement, and annihilation. By exploiting the thickness dependence of the magnetization reversal process, pseudospin valve nanomagnets from two Co50Fe50 thicknesses (10 and 60 nm) were fabricated. We also investigated the effect of interlayer exchange coupling in pseudospin valve structures by varying the Cu spacer layer (tCu). For tCu≤5 nm, the two ferromagnetic layers are found to be strongly coupled by exchange interaction. The strength of the coupling is significantly dependent on temperature. For tCu≥20 nm, the two Co50Fe50 layers are antiferromagnetically coupled at 300 K. As the temperature is reduced below 50 K, we observed a clear transition from antiferromagnetic to ferromagnetic coupling.

Switching and thermal stability properties of bilayer thin films: Single versus multigrain cases

We investigate magnetization reversal and thermal stability (energy barriers) properties of composite media, for a broad range of saturation magnetization values, comparing the case of individual grain and multigrain systems in order to assess the effect of intergranular interactions. For the hard phase we incorporate partially ordered FePt model with realistic representation of exchange interactions as well as a “future recording media” with high anisotropy and low magnetization. The results are presented as a function of the interfacial exchange parameter. We demonstrate that the energy barriers of an individual grain and multigrain thin film show different behavior due to the domain wall formation at the remanence for thin films with low magnetization soft layer. The individual grain presents the most favorable figure of merit for large soft layer magnetization. In contrast, for the multigrain thin film, the best performance corresponds to the case of both low soft and hard layer magnetizations.

Spin reversal in small magnetic elements as a function of orientation in external magnetic field

Monte Carlo simulations are used to investigate magnetization reversal mechanisms and temperature dependence of Hc,ψ. Hc,ψ is the switching field when the external field is directed at an angle ψ to the easy axis. ψ is defined as the acute angle the external field makes with the easy axis, positive ψ corresponding to a counter-clockwise turn from the easy axis. We find different magnetization reversal mechanisms for different ψ and show the role of edge domains. For ψ=−π∕4 and ψ=0 switching occurs by the nucleation of vortices while for ψ=+π∕4 switching occurs by a skewed stretching of the edge domains. Differences in the location and growth of the vortices are reported. Vortices can facilitate switching as evidenced by the low values of Hc,−π∕4. Comparison with known temperature dependencies of Hc,+π∕4 and Hc,0 obtained via theory, simulation and experiment shows that (i) values of Hc,−π∕4 are consistently lower than Hc,+π∕4 and Hc,0 at all temperatures considered and (ii) Hc,−π∕4 has the same linear temperature dependence as Hc,0 but different from the T2 dependence Hc,+π∕4.

Magnetic behavior of exchange-coupledFe30Au70/Fe65Au35bilayers

The evolution of magnetic configurations inside ferromagnetic ${\mathrm{Fe}}_{30}{\mathrm{Au}}_{70}/{\mathrm{Fe}}_{65}{\mathrm{Au}}_{35}$ bilayers have been studied. The two FeAu alloys magnetization are ferromagnetically exchange coupled at the interface and both exhibit an in-plane uniaxial anisotropy. The magnetization reversal of a bilayer from one saturated state to the other occurs via an interface domain wall state, which is metastable. This interface magnetic domain wall which spreads mainly in the soft ${\mathrm{Fe}}_{30}{\mathrm{Au}}_{70}$ layer is pinned at the interface by the harder ${\mathrm{Fe}}_{65}{\mathrm{Au}}_{35}$ alloy. Its presence and its ``compression'' are evidenced by magnetization, electrical transport, and ac-susceptibility measurements combined with a unidimensional micromagnetic calculation. In order to investigate magnetization reversal dynamics, temperature dependence as well as magnetic aftereffect measurements were performed. The magnetization reversal process is found to be thermally activated and activation parameters could be deduced.

Magnetization Reversal beyond the Curie Temperature Considering the Curie-Weiss Law

With consideration to the Curie-Weiss law, we investigate magnetization reversal beyond the Curie temperature, from theoretical to experimental. This paper outlines a theoretical model in accordance with the Curie-Weiss law and also presents a new criterion for the shape stability of recorded domains using magneto-optical recording or hybrid recording. Fairly good agreement was obtained between the theoretical and experimental investigations.

In situ vectorial magnetization reversal study of ultrathin Co films on Pd (111) using magneto-optical Kerr effects

We have investigated magnetization reversal of ultrathin Co/Pd (111) films via in situ determination of three-dimensional magnetization orientations using magneto-optical Kerr effects of p and s waves. We find that with increasing the Co thickness the easy axis of magnetization is switching from normal-to-plane to in-plane through a stable canted phase and magnetization reversal under an applied magnetic field shows very contrastive behavior depending on the easy axis of magnetization. In particular, magnetization reversal via spiral motion is observed in the Co film of the canted phase which could be explained by an existence of in-plane anisotropy and an applied field slightly tilted from the film normal.

Off-axis electron holography of exchange-biased CoFe/FeMn patterned nanostructures

Off-axis electron holography and micromagnetic simulations have been used to investigate magnetization reversal mechanisms and remanent states in exchange-biased submicron Co84Fe16/Fe54Mn46 patterned elements. Domain structures within the elements were characterized despite the narrow thickness (∼3 nm) of the ferromagnetic layer relative to the total element thickness (∼42 nm). Individual elements were able to support different remanent states and their magnetic microstructure was sensitive to their size. The simulations confirmed that the coercivities of the elements and their domain structures were highly sensitive to the strength and orientation of the pinning field. A good fit to the experimental data was provided by using an interface exchange field that had a fixed amplitude and direction in the simulations, and small disagreements were attributed to structural imperfections. These differences emphasize the value of an experimental technique such as electron holography for probing local micromagnetic structure in individual nanostructured elements.

Magnetization reversal in Co/Pd multilayers with varying Co sublayer thickness

We have investigated magnetization reversal in nanostructured Co/Pd multilayers. Interestingly enough, reversal phenomena in this system were found to be very sensitive to the Co-sublayer thickness and very contrasting reversal behaviors were observed between the samples having 2-Å-thick Co and 4-Å-thick Co sublayers. Direct domain observation and time-dependent magnetization viscosity curves revealed the wall-motion dominant reversal in the former samples, and the nucleation dominant reversal in the latter samples. Magnetization reversal in Co/Pd multilayers was theoretically studied by Monte Carlo simulation and experimentally observed reversal behaviors could be well explained.