Change In Magnetic Anisotropy Research Articles

X-ray scattering study on the electric field-induced interfacial magnetic anisotropy modulation at CoFeB / MgO interfaces

The electric field-induced modifications of magnetic anisotropy in CoFeB/MgO systems are studied using X-ray resonant magnetic scattering and magneto-optical Kerr effect. Voltage dependent changes of the magnetic anisotropy of −12.7 fJ/Vm and −8.32 fJ/Vm are observed for Ta/CoFeB/MgO and Hf/CoFeB/MgO systems, respectively. This implies that the interfacial perpendicular magnetic anisotropy is reduced (enhanced) when electron density is increased (decreased). X-ray resonant magnetic scattering measurements reveal that the small in-plane magnetic component of the remanent state of CoFeB/MgO systems with weak magnetic anisotropy changes depending on the applied voltage leading to modification of the magnetic anisotropy at the CoFeB/MgO interface.

Effects on Magnetic Properties of GaMnAs Induced by Proximity of Topological Insulator Bi2Se3

Effects induced by a topological insulator Bi2Se3 on the magnetic properties of an adjacent GaMnAs film have been investigated using transport measurements. We observed three conspicuous effects in the GaMnAs layer induced by the proximity of the Bi2Se3 overlayer. First, our resistivity data as a function of temperature show that the GaMnAs layer adjacent to the Bi2Se3 displayed strongly metallic behavior, as compared with the GaMnAs control specimen. Second, the Curie temperature of the GaMnAs in the bilayer was observed to be higher than that of the control layer, in our case by nearly a factor of two. Finally, we observed significant changes in the in-plane magnetic anisotropy of the GaMnAs in the bilayer, in the form of much higher values of both cubic and uniaxial anisotropy parameters. This latter feature manifests itself in a rather spectacular increase of the coercive field observed in magnetization reversal across the in-plane hard axis. These results suggest that proximity of an adjacent Bi2Se3 layer represents an important tool for modifying and controlling the ferromagnetic properties of GaMnAs film, and could thus be used to optimize this and similar materials for applications in spintronic devices.

Magnetic Properties and the Giant Magnetoimpedance of Amorphous Co-Based Wires with a Carbon Coating

A comparative analysis of the magnetic properties and specific features of the giant magnetoimpedance has been carried out for amorphous rapidly quenched wires with a composition of (Co0.94Fe0.06)72.5Si12.5B15 in the initial state and after the deposition of a carbon coating. The deposition of the defective graphene-like carbon layer was carried out under normal conditions during the exposure in toluene (methylbenzene). The method of the energy-dispersive X-ray spectroscopy made it possible to reliably show that after the modification in toluene, the carbon content on the surface significantly exceeds the natural amount of carbon. The deposition of the carbon coating induced changes in the distribution of the initial quenching stresses in the near-surface layer of amorphous wires. A comparative analysis of the magnetic and magnetoimpedance properties of the samples before and after exposure in the aromatic solvent confirms the occurrence of changes in the effective magnetic anisotropy as a result of this surface treatment.

Reduction in the write error rate of voltage-induced dynamic magnetization switching using the reverse bias method

Using macro-spin modeling, we studied the reduction in the write error rate (WER) of voltage-induced dynamic magnetization switching by enhancing the effective thermal stability of the free layer using a voltage-controlled magnetic anisotropy change. Marked reductions in WER can be achieved by introducing reverse bias voltage pulses both before and after the write pulse. This procedure suppresses the thermal fluctuations of magnetization in the initial and final states. The proposed reverse bias method can offer a new way of improving the writing stability of voltage-driven spintronic devices.

Study of magneto-electric coupling between ultra-thin Fe films and PMN-PT using X-ray magnetic circular dichroism

X-ray absorption spectra and magnetic circular dichroism were measured at the Fe L3, 2-edges of an iron wedge deposited on a ferroelectric substrate in the total electron yield mode. Upon switching the ferroelectric polarization from Pup to Pdown, we observe a relative change in the total magnetic moment of 20% for 1.5 nm thin Fe. For 3 nm thin Fe, the relative change is within the sum rule error bar. Taking the sampling depth of the measurement method into account, this difference is compatible with a magnetic anisotropy change taking place in the first interfacial layer in contact with the ferroelectric substrate. We attribute this interfacial coupling to a charge accumulation or depletion at the interface.

Effect of doping rare earths on magnetostriction characteristics of CoFe2O4 prepared from spent Li-ion batteries

Recovering spent Li-ion batteries is beneficial to the economy and environment. Therefore, this study synthesized nanoparticles of cobalt ferrite doped with different rare earth ions (Nd, Ce, and Pr) by a sol-gel auto-combustion method using spent Li-ion batteries. The effect of the different doping elements on grain sizes, structure, magnetic and magnetostrictive properties, and strain derivative were confirmed by X-ray diffraction, scanning election microscopy, vibrating sample magnetometer, and a magnetostrictive coefficient measuring system. Substitution of a small amount of Fe3+ with RE3+ in CoRExFe2-xO4 (x = 0.025, 0.05, and 0.1) had a large effect on magnetostrictive properties and strain derivative, which was improved compared with pure cobalt ferrite at low magnetic field. The maximum strain derivative (dλ/dH = −1.49 × 10−9 A−1 m at 18 kA m−1) was obtained for Nd, x = 0.05. Changes in the magnetostriction coefficients and strain derivatives were correlated with changes in cation distribution, microstructure, and magnetic anisotropy, which depended strongly on RE3+ substitution and distribution in the spinel structure.

A high-resolution Holocene record of the East Asian summer monsoon variability in sediments from Mountain Ganhai Lake, North China

A high-resolution environmental magnetic records from a sediment profile in Mountain Ganhai Lake, has provided new insights into modulation of the East Asian summer monsoon (EASM) on climatic changes in North China from the final period of last deglacial stage to Holocene. Large pseudo-single-domain (PSD) to multidomain (MD) detrital magnetite grains are identified in the lake samples. The upwards decreasing magnetic susceptibility (χ) and anhysteretic remanent magnetic susceptibility (χARM) are consistent with the dominant vegetation changes: grassland (~13.0–10.5 ka) under dry and cold conditions, shrub-forest-grassland (~10.5–5.8 ka) in a warm and humid climate, and forest where the Pinus trees increase rapidly to be the dominant taxa, indicating the climate changes from warm and humid to cooler but drier between ~5.8 ka and ~4.0 ka. The lower S-100mT and S-300mT ratios coincide with the higher degree of soil stability and a stable lake stage at ~11.8–6.5 ka. Changes in magnetic anisotropy are also linked to environmental and climatic changes, with T parameters showing higher values during warm/interglacial periods. The anisotropy patterns indicate three different stages of the lake evolution: (1) an early stage of the lake, accompanied by a disturbed high-energy flow, a coarse average mineral particle diameter (MPD) distribution (>16.28 μm) and scattered subvertical minimum direction (K3) at ~13.0–11.8 ka; (2) a fairly stable lake environment between ~11.8 ka and 6.5 ka, indicated by a low-energy flow, finer MPD (~9.69 μm) and subvertical K3 axes; (3) an unstable, high-energy flow and coarse MPD (~20.03 μm) with tilted K3 axes, thus indicating a transition from lake-center to lakeside (~6.5–4.0 ka). These multi-proxy records reveal a weak EASM activity in the final period of the last deglaciation (~13.0–11.8 ka), a high EASM intensity in the early-mid Holocene (~11.8–4.8 ka), an EASM maxima in the mid-Holocene (~8.0–5.8 ka), which then generally weakens at ~4.3–4.2 ka. Overall, this study suggests the anisotropy and climatic changes in the alpine lake are significantly affected by the insolation-driven EASM.

Ultrafast laser-induced changes of the magnetic anisotropy in a low-symmetry iron garnet film

We explore a thermal mechanism of changing the anisotropy by femtosecond laser pulses in dielectric ferrimagnetic garnets by taking a low symmetry (YBiPrLu)3(FeGa)5O12 film grown on the (210)-oriented Gd3Ga5O12 substrate as a model media. We demonstrate by means of spectral magneto-optical pump-probe technique and phenomenological analysis, that the magnetization precession in such a film is triggered by laser-induced changes of the growth-induced magnetic anisotropy along with the well-known ultrafast inverse Faraday effect. The change of magnetic anisotropy is mediated by the lattice heating induced by laser pulses of arbitrary polarization on a picosecond time scale. We show that the orientation of the external magnetic field with respect to the magnetization easy plane noticeably affects the precession excited via the anisotropy change. Importantly, the relative contributions from the ultrafast inverse Faraday effect and the change of different growth-induced anisotropy parameters can be controlled by varying the applied magnetic field strength and direction. As a result, the amplitude and the initial phase of the excited magnetization precession can be gradually tuned.

Atomic ordering and coercive force of nanocrystalline Fe-Co alloy films

In single crystal films of the Fe0,5Co0,5 alloys grown by the method of vacuum condensation, a metastable condition may be received that is similar to the completely disordering condition. Approximately during ten days after the condensation in the film at the room temperature the short range and then long range atomic ordering is developed. Simultaneously the changes of magnetic anisotropy, electroresistance and coercive force of the films were investigated. This investigations show that the appearance of the shot range atomic ordering increases the electroresistance of films and the long range atomic ordering reduces it. The dependence of coercive force from time to time at room temperature atomic ordering films Fe0,5Co0,5 alloys, and Fe0,75Co0,25. Found that the biggest change Hc (double) is observed in single-crystal films when changing mechanism of magnetization reverse. Most is a consequence of the changes to the crystallographic anisotropy.

Descriptors of magnetic anisotropy revisited.

The recently discovered thermal elasticity of magnetic anisotropy is not at all an exotic phenomenon. For many lanthanide complexes the qualitative nature of their magnetic anisotropy changes as a function of temperature and magnetic field; for some, even multiple times. The theoretically predicted existence of such multi-switch compounds is experimentally corroborated.

Magnetic properties and giant magnetoimpedance of surface modified Co-based amorphous ribbons with carbon covering

Fe3Co66Cr3Si16B12and Fe6Co60Ni10Si14B10amorphous ribbons were surface modified in toluene at room temperature. Such a treatment resulted in deposition of thin carbon-based layer. As a result of the carbon covering deposition the stress distribution in the near-surface layers was changed due to partial compensation of the initial quenching stresses. Comparative analysis of magnetic and magnetoimpedance properties of as-quenched and surface modified ribbons confirms changes in effective magnetic anisotropy as a result of surface treatment. An increase of the corrosion resistance of the ribbons with carbon covering can be useful for the development amorphous ribbon based magnetic biosensor.

Voltage induced artificial ferromagnetic-antiferromagnetic ordering in synthetic multiferroics

This paper presents numerical and experimental data for dipole-dipole coupled Ni nanodots on a piezoelectric [Pb(Mg1/3Nb2/3)O3]0.68[PbTiO3]0.32 substrate. Simulation results show that the dipole coupling produces artificial ferromagnetic (parallel magnetization alignment in the nanodot arrays) behavior that can be modified to artificial antiferromagnetic behavior with an applied voltage. Experimental results show the trends in Mr and Hc predicted by the model, but discrepancies arise due to geometric defects present in the fabricated samples. Geometric defects are introduced into the Ni nanodot models, thus dramatically improving the correlation between experiments and analysis. This work shows, through numerical simulations, that artificial multiferroic nanostructures can be designed to produce switching from parallel (artificial ferromagnetic) to antiparallel (artificial antiferromagnetic) magnetization ordering by leveraging dipole coupling with voltage induced changes in magnetic anisotropy.

Influence of the magnetization reversal mechanism on the electric field modulation of coercivity in Pt/Co structures

We studied the effect of electric field (EF) on the coercivity of two Pt/Co structures with different Co layer thicknesses. Opposite signs of the coercivity change by the gate voltage application are observed in these samples, whereas the sign of the magnetic anisotropy change is the same. We performed direct observations of the domain structures during magnetization reversal under the gate voltage and found that two samples showed significant differences in the reversal process and EF effect. This result indicates that the sign reversal of the electric field effect on coercivity observed in the present structures originates from the difference in the macroscopic magnetization reversal process.

Voltage Control of Two-Magnon Scattering and Induced Anomalous Magnetoelectric Coupling in Ni-Zn Ferrite.

Controlling spin dynamics through modulation of spin interactions in a fast, compact, and energy-efficient way is compelling for its abundant physical phenomena and great application potential in next-generation voltage controllable spintronic devices. In this work, we report electric field manipulation of spin dynamics-the two-magnon scattering (TMS) effect in Ni0.5Zn0.5Fe2O4 (NZFO)/Pb(Mg2/3Nb1/3)-PbTiO3 (PMN-PT) multiferroic heterostructures, which breaks the bottleneck of magnetostatic interaction-based magnetoelectric (ME) coupling in multiferroics. An alternative approach allowing spin-wave damping to be controlled by external electric field accompanied by a significant enhancement of the ME effect has been demonstrated. A two-way modulation of the TMS effect with a large magnetic anisotropy change up to 688 Oe has been obtained, referring to a 24 times ME effect enhancement at the TMS critical angle at room temperature. Furthermore, the anisotropic spin-freezing behaviors of NZFO were first determined via identifying the spatial magnetic anisotropy fluctuations. A large spin-freezing temperature change of 160 K induced by the external electric field was precisely determined by electron spin resonance.

Electric field effect on magnetic anisotropy for Fe-Pt-Pd alloys

The electric field effect on magnetic anisotropy was investigated for the FePt1-xPdx alloy films with perpendicular magnetic anisotropy. The polar magneto-optical Kerr (p-MOKE) loops were measured under the electric field application in order to evaluate the electric field-induced perpendicular magnetic anisotropy change per area (Δεperpt). A clear change in the saturation field of p-MOKE loop was observed for FePt by varying the applied electric field (ΔE). In the case of FePt, Δεperpt divided by ΔE was evaluated to be -129 (fJ/Vm). We found that the magnitude of Δεperpt / ΔE was significantly reduced with increasing x.

Voltage controlled interfacial magnetism through platinum orbits

Electric fields at interfaces exhibit useful phenomena, such as switching functions in transistors, through electron accumulations and/or electric dipole inductions. We find one potentially unique situation in a metal–dielectric interface in which the electric field is atomically inhomogeneous because of the strong electrostatic screening effect in metals. Such electric fields enable us to access electric quadrupoles of the electron shell. Here we show, by synchrotron X-ray absorption spectroscopy, electric field induction of magnetic dipole moments in a platinum monatomic layer placed on ferromagnetic iron. Our theoretical analysis indicates that electric quadrupole induction produces magnetic dipole moments and provides a large magnetic anisotropy change. In contrast with the inability of current designs to offer ultrahigh-density memory devices using electric-field-induced spin control, our findings enable a material design showing more than ten times larger anisotropy energy change for such a use and highlight a path in electric-field control of condensed matter.

Crossover between axial and radial magnetic anisotropy in self-organized permalloy nanowires

Self-organized permalloy nanowire arrays embedded in hexagonally ordered nanochannels of anodic alumina membranes were produced by electrodeposition. The dimensions of the nanowires were tuned over a wide range by controlling the dimensions of the host alumina templates. Room temperature magnetic hysteresis revealed a considerable dependence of the magnetic anisotropy of the array on the nanowire dimensions. The magnetization direction of the nanowires was found to change from axial to longitudinal direction as both the diameter and length of the wire increased. The observed behavior was ascribed to the increase in magnetostatic coupling among nanowires, as confirmed by first-order reversal curve measurements. Theoretical calculations based on a simple magnetostatic model, which considers the dipolar interaction among the wires, estimated the critical dimensions of the nanowires at which the magnetic anisotropy changes from perpendicular to longitudinal direction.

Significant modification of perpendicular magnetic anisotropy of W/Fe(001) multilayer by controlling in-plane lattice constant

First-principles calculation predicts a large negative to positive change in the intrinsic perpendicular magnetic anisotropy (PMA) on the order of 107 erg/cm3 of a W/Fe(001) multilayer upon reducing the in-plane lattice constant. This PMA arises at the W/Fe interface, and the second interfacial W site plays an important role. To experimentally verify this theoretical prediction, we have grown W/Fe/W(001) epitaxial trilayers on Cr(001) underlayers. By varying the W layer thickness, the in-plane lattice constant of W can be widely controlled, and the large change in PMA from negative to positive is successfully demonstrated.

Scaling of anomalous Hall effect in Ta/CoFeB/MgAl2O4/Ta multilayers

The anomalous Hall effect (AHE) is studied in Ta/CoFeB/MgAl2O4/Ta multilayers with different thicknesses of MgAl2O4 (t), which causes in-plane magnetic anisotropy (IMA) for t = 1.0 nm and perpendicular magnetic anisotropy (PMA) for t ≥ 1.2 nm. Conventional scaling was demonstrated to be not inadequate in our case. The origin of the AHE in Ta/CoFeB/MgAl2O4/Ta multilayers is mainly an extrinsic mechanism. The contribution of skew scattering (SS) is unneglectable, and both the SS and side jump are enhanced when the magnetic anisotropy changes from IMA to PMA, indicating that the oxidation at the interface of CoFeB/MgAl2O4 has a dominant influence on the AHE.

The effect of dynamical compressive and shear strain on magnetic anisotropy in a low symmetry ferromagnetic film

Dynamical strain generated upon excitation of a metallic film by a femtosecond laser pulse may become a versatile tool enabling control of the magnetic state of thin films and nanostructures via inverse magnetostriction on a picosecond time scale. Here, we explore two alternative approaches to manipulate magnetocrystalline anisotropy and excite magnetization precession in a low-symmetry film of a magnetic metallic alloy galfenol (Fe,Ga), either by injecting a picosecond strain pulse into it from a substrate, or by generating dynamical strain of a complex temporal profile in the film directly. In the former case, we realize ultrafast excitation of magnetization dynamics solely by strain pulses. In the latter case, optically-generated strain emerging abruptly in the film modifies its magnetocrystalline anisotropy, competing with heat-induced change of anisotropy parameters. We demonstrate that the optically-generated strain remains efficient for launching magnetization precession, when the heat-induced changes of anisotropy parameters do not trigger the precession any more. We emphasize that in both approaches the ultrafast change of magnetic anisotropy mediating the precession excitation relies on the mixed, compressive, and shear character of the dynamical strain, which emerges due to low-symmetry of the metallic film under study.