Biaxial Anisotropy Research Articles

Study of torque acting on magnetization during 180° pulsed reversal process in ferrite-garnet films with biaxial anisotropy

The mode of 180° a pulsed magnetization reversal process of ferrite-garnet films with in-plane anisotropy in the external fields region, in which the mechanism of the homogeneous rotation of magnetization takes place, was firstly investigated. Analysis of calculated and experimental longitudinal signals showed that the presence of biaxial anisotropy in real ferrite-garnet film leads to the occurrence of nonlinear damped magnetization oscillations (with a period of the main harmonic of ~1.5 ns).

Comparison of Limiting Loop Model and Elemental Operator Model for Magnetic Hysteresis of Ferromagnetic Materials

This paper introduces a comparative study of two different hysteresis models, limiting loop model and elemental operator model. The former is regarded as a mathematical approach based on the traditional Preisach model. To circumvent the difficulty of determining the distribution function in the Preisach model, the data of the limiting hysteresis loop and a function transform on the Preisach diagram are employed. The latter is a physical method which adopts a vectorial elemental operator with biaxial anisotropy based on the magnetization mechanisms of the ferromagnetic material. These two models are analyzed and compared in terms of the underlying principle, numerical implementation, and calculation accuracy in this paper. To verify the introduced models, the magnetic properties of non-oriented silicon steel Lycore-140 and soft magnetic composite material Somaloy 500 under alternating excitations are measured and compared with simulated results, which show the validity and practicability of the models but with different calculation accuracy and speed.

Remarkably enhanced current-driven 360\xb0 domain wall motion in nanostripe by tuning in-plane biaxial anisotropy

By micromagnetic simulations, we study the current-driven 360° domain wall (360DW) motion in ferromagnetic nanostripe with an in-plane biaxial anisotropy. We observe the critical annihilation current of 360° domain wall can be enhanced through such a type of anisotropy, the reason of which is the suppression of out-of-plane magnetic moments generated simultaneously with domain-wall motion. In details, We have found that the domain-wall width is only related to Ky − Kx, with Kx(y) the anisotropy constant in x(y) direction. Taking domain-wall width into consideration, a prior choice is to keep Ky ≈ Kx with large enough K. The mode of domain-wall motion has been investigated as well. The traveling-wave-motion region increases with K, while the average DW velocity is almost unchanged. Another noteworthy feature is that a Walker-breakdown-like motion exists before annihilation. In this region, though domain wall moves with an oscillating behavior, the average velocity does not reduce dramatically, but even rise again for a large K.

Thickness and angular dependent magnetic anisotropy of La0.67Sr0.33MnO3 thin films by Vectorial Magneto Optical Kerr Magnetometry

We investigate the in-plane magnetic anisotropy in La0.67Sr0.33MnO3 thin films grown on SrTiO3 (001) substrate using angular dependent room temperature Vectorial Magneto-Optical Kerr Magnetometry. The experimental data reveals that the magnetic anisotropy symmetry landscape significantly changes depending upon the strain and thickness. At low film thickness (12 and 25 nm) the dominant uniaxial anisotropy is due to interface effects, step edges due to mis-cut angle of SrTiO3 substrate. At intermediate thickness, the magnetic anisotropy presents a competition between magnetocrystalline (biaxial) and substrate step induced (uniaxial) anisotropy. Depending upon their relative strengths, a profound biaxial or uniaxial or mixed anisotropy is favoured. Above the critical thickness, magnetocrystalline anisotropy dominates all other effects and shows a biaxial anisotropy.

On the manifestation of effect of delayed acceleration of the transient process during 180° pulsed magnetization reversal of real ferrite–garnet films with planar anisotropy

The regime of 180° pulsed magnetization reversal of ferrite–garnet films with planar anisotropy in the region of external fields, in which the mechanism of uniform rotation of the magnetization operates, is investigated for the first time. An analysis of the numerical solutions of the Landau–Lifshitz equation and the calculated and experimentally obtained signals showed that the presence of biaxial anisotropy in real ferrite–garnet films leads to the fact that at finite duration of the remagnetizing pulse front the initial slow rotation at definite moment of time is sharply accelerated so that over an interval of ~0.7 ns the azimuthal angle changes from 45° to the equilibrium value (160°–170°). As a result, appearence of the nonlinear damped oscillations of magnetization with a fundamental harmonic period of ~1.5 ns become possible.

Correlations Between Structural and Magnetic Properties of Co2FeSi Heusler-Alloy Thin Films

The structural and magnetic properties of the full Heusler alloy Co2FeSi are its key features for practical applications, but the exact structure-function relationship and underlying mechanism still remain unclear. In this detailed study, experiments and simulations clarify the precise correlations between magnetic parameters and the degree of structural ordering. Enhancement of both biaxial anisotropy and atomic ordering are realized with increasing substrate temperature. These findings are helpful for designing advanced spintronic devices with controllable magnetic anisotropy.

Direct observation of temperature-driven magnetic symmetry transitions by vectorial resolved MOKE magnetometry

Angle- and temperature-dependent vectorial magnetometry measurements are necessary to disentangle the effective magnetic symmetry in magnetic nanostructures. Here we present a detailed study on an Fe(1 0 0) thin film system with competing collinear biaxial (four-fold symmetry) and uniaxial (two-fold) magnetic anisotropies, carried out with our recently developed full angular/broad temperature range/vectorial-resolved magneto-optical Kerr effect magnetometer, named TRISTAN. The data give direct views on the angular and temperature dependence of the magnetization reversal pathways, from which characteristic axes, remanences, critical fields, domain wall types, and effective magnetic symmetry are obtained. In particular, although the remanence shows four-fold angular symmetry for all investigated temperatures (15 K–400 K), the critical fields show strong temperature and angular dependencies and the reversal mechanism changes for specific angles at a given (angle-dependent) critical temperature, showing signatures of an additional collinear two-fold symmetry. This symmetry-breaking is more relevant as temperature increases to room temperature. It originates from the competition between two anisotropy contributions with different symmetry and temperature evolution. The results highlight the importance of combining temperature and angular studies, and the need to look at different magnetic parameters to unravel the underlying magnetic symmetries and temperature evolutions of the symmetry-breaking effects in magnetic nanostructures.

Studying the effect of biaxial anisotropy on nonlinear magnetization oscillations accompanying the 90° pulsed magnetization process in ferrite–garnet films with easy-plane anisotropy

Time dependences of the azimuthal component of the torque T φ(t) acting on magnetization are calculated to understand the nature of the delayed magnetization acceleration effect observed during the 90° pulsed magnetization of real ferrite–garnet films, in which biaxial anisotropy exists alongside with in-plane anisotropy. A calculation technique based on analyzing an operating point trajectory is used. Calculations show that if the effective anisotropy field H K2 is comparable to the magnetizing pulse amplitude H ma, abruptly ascending regions at characteristic times t* in curves T φ(t) arise, in the limit of which nonlinear magnetization oscillations formed. The shape of these regions depends weakly on the magnetizing pulse front duration τf. This explains the reason of the weak dependence of the nonlinear magnetization oscillations on duration of the magnetizing pulse front. Calculations also show that the main features of the delayed acceleration effect are less clear upon an increase of the pulse amplitude: the behavior of curves T φ(t) becomes smoother near times t*, and an increase in the pulse front duration is accompanied by a stronger drop in the intensity of magnetization oscillations.

Magnetic domain configuration of (111)-oriented LaFeO3 epitaxial thin films

In antiferromagnetic spintronics control of the domains and corresponding spin axis orientation is crucial for devices. Here we investigate the antiferromagnetic axis in (111)-oriented LaFeO3/SrTiO3, which is coupled to structural twin domains. The structural domains have either the orthorhombic a- or b-axis along the in-plane ⟨11¯0⟩ cubic directions of the substrate, and the corresponding magnetic domains have the antiferromagnetic axis in the sample plane. Six degenerate antiferromagnetic axes are found corresponding to the ⟨11¯0⟩ and ⟨112¯⟩ in-plane directions. This is in contrast to the biaxial anisotropy in (001)-oriented films and reflects how crystal orientation can be used to control magnetic anisotropy in antiferromagnets.

A Temperature-Dependent Hysteresis Model for Soft Ferrites

This paper introduces a temperature-dependent hysteresis model based on a vectorial elemental operator with temperature-sensitive spontaneous magnetization and biaxial anisotropy for the soft ferrites. Detailed analysis of the temperature-dependent magnetic properties of one elemental operator has been presented thereafter. With the help of the proposed vector elemental operator and the 2-D Gaussian distribution function, the temperature-dependent magnetic hysteresis of soft ferrites can be simulated. This model is validated by the substantial agreement between the simulated and measured major hysteresis loops of a soft ferrite sample Siemens 4C65 at different temperatures with slight acceptable error.

Kilometer-scale fault-related thermal anomalies in tight gas sandstones

Upper Carboniferous sandstones make one of the most important tight gas reservoirs in Central Europe. This study integrates a variety of geothermometers (chlorite thermometry, fluid inclusion microthermometry and vitrinite reflection measurements) to characterize a thermal anomaly in a reservoir outcrop analog (Piesberg quarry, Lower Saxony Basin), which is assumed responsible for high temperatures of circa 300 °C, deteriorating reservoir quality entirely. The tight gas siliciclastics were overprinted with temperatures approximately 90–120 °C higher compared to outcropping rocks of a similar stratigraphic position some 15 km to the west. The local temperature increase can be explained by circulating hydrothermal fluids along the fault damage zone of a large NNW-SSE striking fault with a displacement of up to 600 m in the east of the quarry, laterally heating up the entire exposed tight gas sandstones. The km-scale lateral extent of this fault-bound thermal anomaly is evidenced by vitrinite reflectance measurements of meta-anthracite coals (VRrot ∼ 4.66) and the temperature-related diagenetic overprint. Data suggest that this thermal event and the associated highest coalification was reached prior to peak subsidence during Late Jurassic rifting (162 Ma) based on K-Ar dating of the <2 μm fraction of the tight gas sandstones. Associated stable isotope data from fluid inclusions, hosted in a first fracture filling quartz generation (T ∼ 250 °C) close to lithostatic fluid pressure (P ∼ 1000 bars), together with authigenic chlorite growth in mineralized extension fractures, demonstrate that coalification was not subject to significant changes during ongoing burial. This is further evidenced by the biaxial reflectance anisotropy of meta-anthracite coals. A second event of quartz vein formation occurred at lower temperatures (T ∼ 180 °C) and lower (hydrostatic) pressure conditions (P ∼ 400 bars) and can be related to basin inversion. This second quartz generation might be associated with a second event of illite growth and K-Ar ages of 96.5–106.7 Ma derived from the <0.2 μm fraction of the tight gas sandstones.This study demonstrates the exploration risk of fault-bound thermal anomalies by deteriorating entirely the reservoir quality of tight gas sandstones with respect to porosity and permeability due to the cementation with temperature-related authigenic cements. It documents that peak temperatures are not necessarily associated with peak subsidence. Consequently, these phenomena need to be considered in petroleum system models to avoid, for example, overestimates of burial depth and reservoir quality.

Antiferromagnetic spin current rectifier

It is shown theoretically, that an antiferromagnetic dielectric with bi-axial anisotropy, such as NiO, can be used for the rectification of linearly-polarized AC spin current. The AC spin current excites two evanescent modes in the antiferromagnet, which, in turn, create DC spin current flowing back through the antiferromagnetic surface. Spin diode based on this effect can be used in future spintronic devices as direct detector of spin current in the millimeter- and submillimeter-wave bands. The sensitivity of such a spin diode is comparable to the sensitivity of modern electric Schottky diodes and lies in the range 102-103 V/W for 30×30 nm2 structure.

Modeling and Measurement of Magnetic Hysteresis of Soft Magnetic Composite Materials Under Different Magnetizations

The soft magnetic composite (SMC) materials and their application in electromagnetic devices have undergone significant development due to their unique advantages, such as low eddy-current loss, quasi-isotropy of mechanical and magnetic properties, low cost, and low material consumption during the production process. However, the magnetic properties of the SMC materials are very different from that of the laminated SiFe materials, which are particularly challenging for the design and application of electrical machines. This paper presents the modeling and measurement of magnetic properties of the SMC materials under both alternating and rotational magnetic excitations. Based on the underlying magnetization mechanisms, a vectorial elemental operator with biaxial anisotropy is introduced, and the concept of distribution function is utilized to describe the density of operators in the specimen. To verify this proposed model, the magnetic hysteresis of the SMC material is simulated and compared with the experimental results obtained by the three-dimensional magnetic property measurement system. The good agreement shows the validity and practicability of this vectorial elemental operator.

Exploring performance, coherence, and clocking of magnetization in multiferroic four-state nanomagnets

Nanomagnetic memory and logic are currently seen as promising candidates to replace current digital computing architectures due to its superior energy-efficiency, non-volatility and propensity for highly dense and low-power applications. In this work, we investigate the use of shape engineering (concave and diamond shape) to introduce biaxial anisotropy in single domain nanomagnets, giving rise to multiple easy and hard axes. Such nanomagnets, with dimensions of ∼100nm×100nm, double the logic density of conventional two-state nanomagnetic devices by encoding more information (four binary bits: “00”, “11”, “10”, “01”) per nanomagnet and can be used in memory and logic devices as well as in higher order information processing applications. We study reliability, magnetization switching coherence, and show, for the first time, the use of voltage-induced strain for the clocking of magnetization in these four-state nanomagnets. Critical parameters such as size, thickness, concavity, and geometry of two types of four-state nanomagnets are also investigated. This analytical study provides important insights into achieving reliable and coherent single domain nanomagnets and low-energy magnetization clocking in four-state nanomagnets, paving the way for potential applications in advanced technologies.

Mueller matrix characterization of flexible plastic substrates

This work reports on Mueller matrix spectroscopic ellipsometry characterization of various flexible plastic substrates that are optically anisotropic with varying degrees of birefringence. The samples are divided into three groups according to the suggested characterization strategy: low birefringence, high birefringence, and twisted birefringence. The first group includes poly(methyl methacrylate) and cyclic olefin copolymer substrates. These are modeled with biaxial anisotropy for the real part of the refractive index while the imaginary part is approximated as isotropic due to small light absorption. The second group includes polyethylene terephthalate and polyethylene naphthalate substrates, which are modeled with biaxial anisotropy for both real and imaginary refractive indices. Lastly, a polyimide substrate is described as two birefringent layers with twisted in-plane orientation.

Non-monotonic probability of thermal reversal in thin-film biaxial nanomagnets with small energy barriers

The goal of this paper is to investigate the short time-scale, thermally-induced probability of magnetization reversal for an biaxial nanomagnet that is characterized with a biaxial magnetic anisotropy. For the first time, we clearly show that for a given energy barrier of the nanomagnet, the magnetization reversal probability of an biaxial nanomagnet exhibits a non-monotonic dependence on its saturation magnetization. Specifically, there are two reasons for this non-monotonic behavior in rectangular thin-film nanomagnets that have a large perpendicular magnetic anisotropy. First, a large perpendicular anisotropy lowers the precessional period of the magnetization making it more likely to precess across the x^=0 plane if the magnetization energy exceeds the energy barrier. Second, the thermal-field torque at a particular energy increases as the magnitude of the perpendicular anisotropy increases during the magnetization precession. This non-monotonic behavior is most noticeable when analyzing the magnetization reversals on time-scales up to several tens of ns. In light of the several proposals of spintronic devices that require data retention on time-scales up to 10’s of ns, understanding the probability of magnetization reversal on the short time-scales is important. As such, the results presented in this paper will be helpful in quantifying the reliability and noise sensitivity of spintronic devices in which thermal noise is inevitably present.

Epitaxial magnetite nanorods with enhanced room temperature magnetic anisotropy.

Nanostructured magnetic materials with well-defined magnetic anisotropy are very promising as building blocks in spintronic devices that operate at room temperature. Here we demonstrate the epitaxial growth of highly oriented Fe3O4 nanorods on a SrTiO3 substrate by hydrothermal synthesis without the use of a seed layer. The epitaxial nanorods showed biaxial magnetic anisotropy with an order of magnitude difference between the anisotropy field values of the easy and hard axes. Using a combination of conventional magnetometry, transverse susceptibility, magnetic force microscopy (MFM) and magneto-optic Kerr effect (MOKE) measurements, we investigate magnetic behavior such as temperature dependent magnetization and anisotropy, along with room temperature magnetic domain formation and its switching. The interplay of epitaxy and enhanced magnetic anisotropy at room temperature, with respect to randomly oriented powder Fe3O4 nanorods, is discussed. The results obtained identify epitaxial nanorods as useful materials for magnetic data storage and spintronic devices that necessitate tunable anisotropic properties with sharp magnetic switching phenomena.

Eigenfrequencies and Modal Analysis of Uniaxial, Biaxial, and Gyroelectric Spherical Cavities

The normalized eigenfrequencies in spherical cavities filled with uniaxial, biaxial, and gyroelectric medium are calculated, and the corresponding modal analysis is performed. A discrete eigenfunction approach is employed that permits the direct calculation of the normalized eigenfrequencies. First, a discrete basis that depends on the tensorial permittivity elements is constructed for expansion of the unknown electric field inside the cavity. Then, the boundary condition is applied on the perfect electric conductor at the cavity's surface, which leads to two infinite sets of homogeneous equations. It is found that the uniaxial/biaxial cavities maintain quasi-TM r , quasi-TE r , as well as hybrid modes, but when the medium becomes gyroelectric, the modes are purely hybrid. The proposed approach is validated against other eigenmode solvers, up to the biaxial anisotropy. The normalized eigenfrequencies of uniaxial, biaxial, and gyroelectric filled cavities are presented and the corresponding eigenmodes are discussed.

Accounting of the Elasticity Modules Anisotropy in HSP Metals for X-Ray Investigations of Dislocation Structure

A calculation of X-ray diffraction on the dislocation structure of polycrystalline materials with the biaxial anisotropy of the crystal lattice has been carried out. The task was reduced to definition of the field of lattice distortion in this neighborhood applied to edge dislocations of the «c» type in condition of anisotropy of elastic modules of a crystal. As a result of general solution of this task, a parameter of spatial anisotropy of the distortion field was defined from elastic modules and further included into tensors of transformation of both initial isotropic model of this field and its coordinates. According to this principle a modified mathematical model of the field of elastic atomic displacements in the neighborhood of an edge dislocation has been built. The final result shows that this anisotropy entirely reflects onto dislocation specific parameters of distortion that can be obtained by an XRD method for determination dislocation distributions and density. It is noted that for hcp metals widely used, accounting of this anisotropy would be reduced to small corrections of parameters.

A separation of antiferromagnetic spin motion modes in the training effect of exchange biased Co/CoO film with in-plane anisotropy

The motion of antiferromagnetic interfacial spins is investigated through the temperature evolution of training effect in a Co/CoO film with in-plane biaxial anisotropy. Significant differences in the training effect and its temperature dependence are observed in the magnetic easy axis and hard axis (HA) and ascribed to the different motion modes of antiferromagnetic interfacial spins, the collective spin cluster rotation (CSR) and the single spin reversal (SSR), caused by different magnetization reversal modes of ferromagnetic layer. These motion modes of antiferromagnetic spins are successfully separated using a combination of an exponential function and a classic n−1/2 function. A larger CSR to SSR ratio and a shorter lifetime of CSR found in the HA indicates that the domain rotation in the ferromagnetic layer tends to activate and accelerate a CSR mode in the antiferromagnetic spins.