Anisotropic Contributions Research Articles

The Influence of Crystal Anisotropy on the Characteristics of Solitary Waves in the Nonlinear Supratransmission Effect: Molecular Dynamic Modeling

This study examines the mechanism of nonlinear supratransmission (NST), which involves the transfer of disturbance to discrete media at frequencies not supported by the structure. We considered a model crystal with A3B stoichiometry. The investigation was carried out using atomistic modeling through molecular dynamics. The interatomic interaction was determined by a potential obtained through the embedded atom method, which approximates the properties of the Pt3Al crystal. The effect of NST is an important property of many discrete structures. Its existence requires the discreteness and nonlinearity of the medium, as well as the presence of a forbidden zone in its spectrum. This work focuses on the differences in the NST effect due to the anisotropy of crystallographic directions. Three planes along which the disturbance caused by NST propagated were considered: (100), (110), and (111). It was found that the intensity of the disturbance along the (100) plane is an order of magnitude lower than for more densely packed directions. Differences in the shape of solitary waves depending on the propagation direction were shown. Moreover, all waves can be described by a single equation, being a solution of the discrete variational equations of macroscopic and microscopic displacements, with different parameters, emphasizing the unified nature of the waves and the contribution of crystal anisotropy to their properties. Studying the NST phenomenon is essential due to numerous applications of the latter, such as implications in information transmission and signal processing. Understanding how disturbances propagate in discrete media could lead to advancements in communication technologies, data storage, and signal amplification where the earlier mentioned ability to describe it with analytical equations is of particular importance.

High temperature magnetic and structural transformations in Fe-Pd nanowires

The microstructure and the hysteresis properties of Fe-Pd nanowire arrays were studied in the as-electrodeposited condition at 300 K, and as functions of temperature after a thermal cycle between 300 K and 950 K. Fe36Pd64 and Fe65Pd35 nanowires, 200 nm in diameter and 7–10 μm long, were electrodeposited into commercial 26 % porosity alumina templates. Initially, the main magnetic phase in both arrays is the metastable γ-Pd(Fe) disordered phase. After a thermal cycle up to 950 K the microstructures transform into a majority ferromagnetic ordered phase (FePd3 in Fe36Pd64 and Fe3Pd in Fe65Pd35) embedding γ-Pd(Fe) remaining grains. Curie temperatures result 500 K, 550 K and 900 K for Fe3Pd, FePd3 and γ-Pd(Fe), respectively. The temperature dependence of the magnetic properties exhibits two stages: one below 500–550 K, when the two phases are ferromagnetic and another one above this temperature when only the minority γ-Pd(Fe) is ferromagnetic. Coercivity and remanence exhibit a maximum near the Curie temperature of the corresponding ordered phase. The effective magnetic anisotropy Keff remains high up to the magnetic transition (ferro to paramagnetic) of the ordered phase, due to the contribution of the magnetocrystalline anisotropy of these relatively hard phases. At higher temperature, the effective anisotropy mainly arises from the magnetostatic (shape and inter-wire dipolar interactions) contribution of the minority phase. The polarization reversal mechanism in the γ-Pd(Fe) phase is found to be the nucleation of inverse magnetic domains and the further expansion of the domain walls into the ferromagnetic grains, surrounded by the paramagnetic ordered phase.

Microstructure, ferromagnetic resonance, and electrical analysis of Ho-substituted Li-Ni nanoparticles

The substitution of rare earth ions is a novel approach to vary the dynamic magnetic properties of soft ferrites to such an extent that its electrical properties and ferromagnetic resonance (FMR) response can be set over a broad frequency range. In this work, a complete transmission electron microscopy (TEM), scanning electron microscopy (SEM), ferromagnetic resonance spectroscopy (FMR), X-ray photoelectron spectroscopy (XPS), and current-voltage (I-V) analysis of holmium (Ho) substituted lithium-nickel soft ferrites with composition Li1.2Ni0.4Fe2−xHoxO4 (x = 0, 0.03, 0.06, 0.09, 0.12, and 0.15) is carried out. TEM analysis reveals a spherical shape distribution of nanoparticles with a particle size of ∼ 50 nm. FMR study is carried out to check the role of Ho addition on magnetic energy losses, FMR line position, and shape. The shift in FMR line shape is mainly attributed to the anisotropy contribution, relaxation processes, and ferromagnetic interactions between the magnetic nanoparticles. XPS experiments confirm the presence of all compositional elements along their valence states. The Ho substitution increased the electrical resistivity, whereas the damping of A-B exchange interactions resulted in a decline of Curie temperature (Tc), which is required for high-frequency power applications.

Anisotropic ultra-compact object in Serrano–Liska gravity model

We implement a recent model proposed by Serrano–Liska (SL) (Alonso-Serrano and Liška, JHEP, 12:196, 2020) to study the ultra-compact star properties. The matter in the interior star is modeled by the quark model, deducted from QCD theory equipped with anisotropic pressure. Anisotropy is used to increase the compactness of the stars. We intend to see the signature of the “quantum gravity” effect through the SL model in ultra-compact stars. The SL model was motivated by quantum correction appearing in the black hole by adding a logarithmic term in gravity entropy used to derive the effective Einstein field equation. We expect this correction term in the SL model also affects ultra-compact star properties. The SL model with coupling constant {tilde{c}} in logarithmic term equipped with spherically symmetric metric yields correction terms mathscr {O}({tilde{c}}) that can be expressed by a function varXi (r). The varXi (r) function vanishes at the star’s exterior. We found that the mass-radius relation prediction by the SL model with anisotropic matter deviates from the one predicted by the standard Tolman–Oppenheimer–Volkoff (TOV) equation for {tilde{c}}ge 10^7 m^2. We also have a sufficiently deep enough effective potential to produce a quasi-normal mode. We obtain the echo frequency of 15.2 kHz using maximum anisotropic pressure contribution and {tilde{c}}= 10^7 m^2. Because the corresponding effective potential is almost indistinguishable from that of GR, this echo frequency value can be indistinguishable to one of GR, but not comparable to the result from GW170817 data analysis, i.e., 72 Hz. To circumvent this problem, we can decrease the value of echo frequency by increasing the magnitude of {tilde{c}} to orders of magnitude than {tilde{c}}= 10^7 m^2. On the other hand, too large a strength from the logarithmic correction term is not physically favored because we learn from the black hole case that the logarithmic term is expected to be smaller than that of the Bekenstein term. Therefore, more precise gravitation echo measurements are crucial to understand this issue.

Interplay between Anisotropy- and Skewness-driven Whistler Instabilities in the Solar Wind under the Core–Strahlo Model

Temperature anisotropy and field-aligned skewness are commonly observed nonthermal features in electron velocity distributions in the solar wind. These characteristics can act as a source of free energy to destabilize different electromagnetic wave modes, which may alter the plasma state through wave–particle interactions. Previous theoretical studies have mainly focused on analyzing these nonthermal features and self-generated instabilities individually. However, to obtain a more accurate and realistic understanding of the kinetic processes in the solar wind, it is necessary to examine the interplay between these two energy sources. By means of linear kinetic theory, in this paper we investigate the excitation of the parallel propagating whistler mode, when it is destabilized by electron populations exhibiting both temperature anisotropy and field-aligned strahl or skewness. To describe the solar wind electrons, we adopt the core–strahlo model as an alternative approach. This model offers the advantage of representing the suprathermal features of halo and strahl electrons, using a single skew–kappa distribution already known as the strahlo population. Our findings show that when the electron strahlo exhibits an intrinsic temperature anisotropy, this suprathermal population becomes a stronger and more efficient source of free energy for destabilizing the whistler mode. This suggests the greater involvement of the anisotropic strahlo in processes conditioned by wave–particle interactions. The present results also suggest that the contribution of core anisotropy can be safely disregarded when assessing the importance of instabilities driven by the suprathermal population. This allows for a focused study, particularly regarding the regulation of the electron heat flux in the solar wind.

(Invited) Anisotropic Contributions in the Chromatographic Elution Behavior of Fullerenes and Fullertubes

Since their discovery in the mid-1980s, the fullerenes have been confined to molecules of less than 100 atoms. With the recent development of a method allowing the isolation of pristine samples[1], the discovery of increasingly long fullertubes, hybrid between a fullerene and a nanotube, is stimulating renewed interest in the field of fullerene science. The increase in the number of atoms comes at a price, the explosion in the number of possible isomers, among which we must identify the experimentally isolated structure. Fuch’s model[2] is commonly used to explain the interaction between fullerenes and non-polar HPLC columns. Still, this approach cannot always differentiate between isomers as the results depend only on the average polarizability, which varies little for fullerenes with the same number of carbon atoms.In this presentation, we will discuss the use of polarizability anisotropy to differentiate isomers in the context of chromatographic elution. It allows us to generalize Fuchs’ model by adding anisotropic contributions leading to a finer description of fullerenes elution behavior and a better isomeric identification.[1] R.M. Koenig, H.-R. Tian, T.L. Seeler, K.R. Tepper, H.M. Franklin, Z.-C. Chen, S.-Y. Xie, and S. Stevenson, J. Am. Chem. Soc. 142, 15614 (2020).[2] D. Fuchs, H. Rietschel, R.H. Michel, A. Fischer, P. Weis, and M.M. Kappes, J. Phys. Chem. 100, 725 (1996). Figure 1

Magneto-transport behavior of disordered three dimensional NixCo1−x inverse opal networks

Herein we report on the magneto-transport properties of disordered three dimensional inverse opals (3D-IOs) fabricated by a standard three-probe electrodeposition technique into the interstices of porous membranes made of 150 nm diameter self assembled poly(methyl methacrylate) spheres. This approach has allowed the synthesis of large scale nanocomposites with exact ferromagnetic NixCo1−x alloy compositions and complex interconnected structure. Particularly, the microstructure of Co-rich 3D-IOs is consistent with the hexagonal close packed hcp texture and its corresponding magnetoresistance is explained in terms of the hcp Co magnetocrystalline anisotropy contribution. Conversely, the magnetoresistive behavior of Ni-rich 3D-IO networks is explained in terms of only their magnetostatic field. The control of these features is made possible by the reduced dimensions of necks and walls, in the 40 nm to 60 nm range, of the 3D-IO structure. Despite the disordered morphology of these 3D-IO nanoarchitectures, their microstructural and magneto-transport properties can be fine tuned due to the reduced nanoscale dimensions of the electrical interconnections. These properties have been found to be comparable to those obtained in other 3D networks, making them interesting systems for their potential use for magnetic sensing and spintronic applications.

Crossover from Positive to Negative Spin Hall Signal in a Ferromagnetic Metal Induced by the Magnetization Modulated Interface Effect

AbstractThe spin Hall effect and its inverse (SHE/ISHE), describing the charge‐to‐spin interconversion, are of critical importance to the fundamental physics involving spin‐orbit coupling and the application of spintronic devices. These phenomena in nonmagnetic materials are reasonably understood after extensive studies. In ferromagnetic metals, however, the fundamental issue of generation and transport of pure spin current, especially the interplay of charge‐to‐spin interconversion and magnetization, is as‐yet poorly understood. Here, direct experimental evidence for the sign change in ISHE by injecting a spin current from Y3Fe5O12 into a Fe film via a Cu spacer is reported. The sizable negative ISHE signal (VISHE) in nanometer‐thick Fe films reverses its sign with a comparable magnitude when Fe magnetization is varied from a longitudinal to transverse orientation with respect to spin current polarization. With decreasing Fe thickness, this negative longitudinal VISHE increases rapidly to a larger positive value in magnitude. The opposite spin Hall angles for longitudinally and transversely polarized spin currents are reproduced by first‐principles transport calculations and the sign change is attributed to the anisotropic contribution at the ferromagnetic interface. This work lays a firm foundation for manipulating spin‐to‐charge interconversion with an extra degree of freedom of magnetization orientation through ferromagnetic metals.

Effect of cold rolling and annealing on the microstructure and mechanical properties of Mn-substituted-for-Ni alumina-forming austenitic stainless steel

The microstructural evolution of low-Ni alumina-forming austenitic (8Mn-AFA) steel during cold rolling with different reductions (from 45% to 80%) and annealing was investigated using electron backscatter diffraction (EBSD) and X-ray diffraction (XRD) techniques. Compared with conventional AFA steel (low Mn content), 8Mn-AFA steel exhibits a higher strength in the transverse direction (TD) than in the rolling direction (RD) during plastic deformation. This anisotropy increases with the cold rolling deformation. When the cold rolling deformation increases from 45% to 80%, the ultimate tensile strength (Rm) in the RD and TD increases from 1091 to 1306 MPa and from 1162 to 1442 MPa, respectively. The stacking fault energy (SFE) of 8Mn-AFA steel is only 46.79 mJ/m2 due to the substitution of 8Mn for Ni. The low SFE induces the formation of many deformation twins arranged along or close to the TD (the angle between them is less than 30°) in the austenite grain, yielding a higher strength in the TD than in the RD. Compared with cold-rolled samples, Rp and Rm decrease in annealed samples, and the anisotropy in the TD and RD almost disappear as the number of deformation twins decreases. The high strength of the cold-rolled 8Mn-AFA steel can be attributed to the dislocation enhancement, grain boundary enhancement, and texture-induced anisotropy strengthening. The dislocation enhancement contributes the most to the strength, exceeding 70%, followed by grain boundary contribution, about 6.9 – 10.8%, while the contribution of texture-induced anisotropy is 5 – 9.2%.

Anisotropy free energy contribution of the ferroelectric domain dynamics in PMN‐PT and PIN‐PMN‐PT relaxor ferroelectrics

AbstractA direct correlation between the materials property behavior with its associated ferroelectric domain mechanisms and the anisotropic component of the Landau free energy is established for binary PMN‐PT (generation I) and ternary PIN‐PMN‐PT (generation II) relaxor ferroelectric single crystal material systems. In addition to their trade‐off in material properties, the observed ferroelectric domain dynamic and the determined free energy anisotropies, especially as approaching phase transition, provide direct insights into the materials field‐dependent behavior between the binary and ternary ferroelectric systems. Domain configuration features such as lamellar structures in binary PMN‐PT and concentric oval‐like structures in ternary PIN‐PMN‐PT result in different material responses to external stimuli. Compared to binary PMN‐PT, the concentric oval‐like domain structures of ternary PIN‐PMN‐PT result in a 20°C higher temperature range of field‐dependent linear behavior, 40% increase in coercive electric field higher elastic stiffness during ferroelectric domain switching, and lower electromechanical energy losses. Separation of the isotropic and anisotropic components in the Landau free energy reveals a higher anisotropic free energy contribution from the ternary system, especially at temperature for practical applications. The high anisotropic free energy found in the ternary PIN‐PMN‐PT system implies that the concentric oval‐like domain structure contributes to reduced electromechanical energy losses and enhanced stability under external applied fields.

Multinuclear solid state nuclear magnetic resonance for studying CsPbBr3 nanocubes

Abstract Cesium lead bromide perovskite (CsPbBr3) nanocrystals have raised impressive interest as efficient and stable optoelectronic materials. Size and morphology play important roles in the final performances of these materials and advanced characterization studies are needed to elucidate structural and surface properties. In this work, CsPbBr3 cubic nanocrystals were obtained by colloidal synthesis and characterized by multinuclear Solid State NMR (SSNMR), complemented by X-Ray Diffraction (XRD), Transmission Electron Microscopy (TEM) and optical spectroscopy. The multinuclear NMR approach allowed the different components of the nanocubes to be separately observed. In particular, the surface ligands and their interactions with the nanocubes surface were investigated by 1H and 13C NMR experiments, while the structural investigation of the perovskite nanocubes was addressed by exploiting 207Pb and 133Cs spectral properties in comparison with bulk CsPbBr3. Static 207Pb NMR spectra indicated a possible contribution of chemical shift anisotropy from the 207Pb nuclei of the outer layer. The 133Cs NMR spectra showed signals with different chemical shifts for cesium atoms in at least three regions of the nanocubes, from the inner core to the surface, which were interpreted in terms of cubic layers with different distances from the surface using a simple geometrical model. This interpretation was also supported by 133Cs longitudinal relaxation time measurements.

Anisotropic thermal property characterizations and optical phonon contribution analysis of ZnO under high pressure

Zinc oxide (ZnO) is a wide band-gap semiconductor material with versatile applications in high-tech fields. Under high pressure, ZnO exhibits multiple phase transitions, which are of great significance for the development of photocatalysts, micro-devices with stress-controlled elements, and the investigation of relevant structure-activity relationships. However, previous studies have reported only theoretical calculations of its thermal transport properties under high pressure due to the challenges of experimental methodology. In this work, we employed a combination of the time-domain thermoreflectance technique and diamond anvil cell to characterize the anisotropic thermal properties of ZnO crystal under 0–20 GPa. Simultaneously, we studied the micro-structure of ZnO in the same pressure range by Raman spectra. Our proposed modified Leibfried-Schlomann equation adequately explained the non-monotonic trend of the thermal conductivity within 10 GPa observed in measurement results. Additionally, we report the ZnO thermal conductivity during the decompression process for the first time. Our experimental results and theoretical analysis advance the understanding of the thermal transport mechanism of wide-gap semiconductors under high pressure and pave the way for their high-pressure modification.

Response of the Einstein Telescope to Doppler anisotropies

We study the response function of the Einstein Telescope to kinematic Doppler anisotropies, which represent one of the guaranteed properties of the stochastic gravitational wave background. If the frequency dependence of the stochastic background changes slope within the detector frequency band, the Doppler anisotropic contribution to the signal can not be factorized in a part depending on frequency, and a part depending on direction. For the first time, we study the detector response function to Doppler anisotropies without making any factorizable Ansatz. Moreover, we do not assume that kinematic effects are small, and we derive general formulas valid for any relative velocity among frames. We apply our findings to three well-motivated examples of background profiles; power-law, broken power-law, and models with a resonance motivated by primordial black hole scenarios. We derive the signal-to-noise ratio associated with an optimal estimator for the detection of nonfactorizable kinematic anisotropies, and we study it for representative examples.

Soft Matter under Pressure: Pushing Particle-Field Molecular Dynamics to the Isobaric Ensemble.

Hamiltonian hybrid particle-field molecular dynamics is a computationally efficient method to study large soft matter systems. In this work, we extend this approach to constant-pressure (NPT) simulations. We reformulate the calculation of internal pressure from the density field by taking into account the intrinsic spread of the particles in space, which naturally leads to a direct anisotropy in the pressure tensor. The anisotropic contribution is crucial for reliably describing the physics of systems under pressure, as demonstrated by a series of tests on analytical and monatomic model systems as well as realistic water/lipid biphasic systems. Using Bayesian optimization, we parametrize the field interactions of phospholipids to reproduce the structural properties of their lamellar phases, including area per lipid, and local density profiles. The resulting model excels in providing pressure profiles in qualitative agreement with all-atom modeling, and surface tension and area compressibility in quantitative agreement with experimental values, indicating the correct description of long-wavelength undulations in large membranes. Finally, we demonstrate that the model is capable of reproducing the formation of lipid droplets inside a lipid bilayer.

Effect of High-Anisotropic Co2+ Substitution for Ni2+ on the Structural, Magnetic, and Magnetostrictive Properties of NiFe2O4: Implications for Sensor Applications.

This work reports on the effect of substituting a low-anisotropic and low-magnetic cation (Ni2+, 2μB) by a high-anisotropic and high-magnetic cation (Co2+, 3μB) on the crystal structure, phase, microstructure, magnetic properties, and magnetostrictive properties of NiFe2O4 (NFO). Co-substituted NFO (Ni1-xCoxFe2O4, NCFO, 0 ≤ x ≤ 1) nanomaterials were synthesized using glycine-nitrate autocombustion followed by postsynthesis annealing at 1200 °C. The X-ray diffraction measurements coupled with Rietveld refinement analyses indicate the significant effect of Co-substitution for Ni, where the lattice constant (a) exhibits a functional dependence on composition (x). The a-value increases from 8.3268 to 8.3751 Å (±0.0002 Å) with increasing the "x" value from 0 to 1 in NCFO. The a-x functional dependence is derived from the ionic-size difference between Co2+ and Ni2+, which also induces grain agglomeration, as evidenced in electron microscopy imaging. The chemical bonding of NCFO, as probed by Raman spectroscopy, reveals that Co(x)-substitution induced a red shift of the T2g(2) and A1g(1) modes, and it is attributed to the changes in the metal-oxygen bond length in the octahedral and tetrahedral sites in NCFO. X-ray photoelectron spectroscopy confirms the presence of Co2+, Ni2+, and Fe3+ chemical states in addition to the cation distribution upon Co-substitution in NFO. Chemical homogeneity and uniform distribution of Co, Ni, Fe, and O are confirmed by EDS. The magnetic parameters, saturation magnetization (MS), remnant magnetization (Mr), coercivity (HC), and anisotropy constant (K1) increased with increasing Co-content "x" in NCFO. The magnetostriction (λ) also follows a similar behavior and almost linearly varies from -33 ppm (x = 0) to -227 ppm (x = 1), which is primarily due to the high magnetocrystalline anisotropy contribution from Co2+ ions at the octahedral sites. The magnetic and magnetostriction measurements and analyses indicate the potential of NCFO for torque sensor applications. Efforts to optimize materials for sensor applications indicate that, among all of the NCFO materials, Co-substitution with x = 0.5 demonstrates high strain sensitivity (-2.3 × 10-9 m/A), which is nearly 2.5 times higher than that obtained for their intrinsic counterparts, namely, NiFe2O4 (x = 0) and CoFe2O4 (x = 1).

Influence of substrate on interfacial Dzyaloshinskii-Moriya interaction in epitaxial Tm3Fe5O12 films

The interfacial Dzyaloshinskii-Moriya interaction (iDMI) promotes homochiral magnetic structures such as N\'eel-type domain walls (DWs) and skyrmions. iDMI as well as chiral magnetic structures have been demonstrated in metal/garnet heterostructures offering desirable properties for spintronic applications compared to their metallic counterparts. By measuring the motion of DWs as a function of current and in-plane magnetic field, we show that for 6.6 nm thick epitaxial thulium iron garnet films with perpendicular magnetic anisotropy grown on gallium garnet substrates, the iDMI and the DW width depend on the substrate but do not scale linearly with lattice mismatch strain. The largest iDMI was $0.007 \mathrm{mJ} {\mathrm{m}}^{\ensuremath{-}2}$, obtained for three substrates of different compositions. The total anisotropy, however, does increase linearly with lattice parameter, indicating a dominant magnetoelastic anisotropy contribution. The sensitivity of iDMI and anisotropy to substrate composition provides opportunities for engineering homochiral magnetic structures and their dynamics.

Crystallographic texture and phase structure induced excellent piezoelectric performance in KNN‐based ceramics

AbstractIt is difficult to maintain strong piezoelectric properties over a wide temperature range in (K,Na)NbO3 (KNN)‐based ceramics owing to the polymorphic phase boundary (PPB). Here, we propose advantageously utilizing the synergistic effect of crystal orientation and phase structure to address this issue. The 〈0 0 1〉pc textured (1 − x)(K0.48Na0.52)(Nb0.96Sb0.04)O3–x(Bi0.5Ag0.5)ZrO3 (KNNS–xBAZ) ceramics with different phase structures were synthesized via the templated grain growth method. A high piezoelectric coefficient (d33) of 505 ± 25 pC/N, an electric field‐induced strain of 0.21%, and a superior temperature stability (d33 exhibited a high retention of ≥78% at the temperature up to 200°C; strain maintained within 5.7% change over a temperature range of 30–150°C) were simultaneously achieved in textured KNNS–0.03BAZ ceramics. The flattened Gibbs free energy induced by the R–O–T multiphase coexistence, the strong anisotropy of crystals, and the abundant nanodomains contributed to the enhanced piezoelectric properties. The contribution of the strong anisotropy of crystals in 〈0 0 1〉pc textured ceramics compensates for the deterioration of the piezoelectric properties caused by the phase structure deviation from the PPB with increasing temperature, which benefits the superior temperature stability of the textured KNNS–0.03BAZ ceramics. The previous merits prove that utilizing the synergistic effect of crystal orientation and phase structure is an effective strategy to boost the piezoelectricity and their temperature stability of KNN‐based ceramics.

A strain-controlled magnetostrictive pseudo spin valve

Electric-field control of magnetism via an inverse magnetostrictive effect is an alternative path toward improving energy-efficient storage and sensing devices based on a giant magnetoresistance effect. In this Letter, we report on lateral electric-field driven strain-mediated modulation of magnetotransport properties in a Co/Cu/Py pseudo spin valve grown on a ferroelectric 0.7Pb[Mg1/3Nb2/3)]O3–0.3PbTiO3 substrate. We show a decrease in the giant magnetoresistance ratio of the pseudo spin valve with the increase in the electric field, which is attributed to the deviation of the Co layer magnetization from the initial direction due to strain-induced magnetoelastic anisotropy contribution. Additionally, we demonstrate that strain-induced magnetic anisotropy effectively shifts the switching field of the magnetostrictive Co layer, while keeping the switching field of the nearly zero-magnetostrictive Py layer unaffected due to its negligible magnetostriction. We argue that magnetostrictively optimized magnetic films in properly engineered multilayered structures can offer a path to enhancing the selective magnetic switching in spintronic devices.

Magnetic behavior and chaining of strontium ferrite-nylon composite above the melting temperature

To better understand Magnetic Field Assisted Additive Manufacturing (MFAAM) the effect of a magnetic field on the orientation and distribution of magnetic particles in a molten magnetic composite was studied. Vibrating Sample Magnetometer (VSM) measurements were made on Sr-ferrite/PA12 fused deposition modeling filaments of different packing fraction (5 and 40 wt. %). The rotation of the sample’s magnetic moment upon application of a field perpendicular to the easy axis was monitored with a biaxial VSM above the PA12’s softening temperature. The observed magnetic moment transients depend on the temperature, the applied alignment field, the packing fraction, and the initial field-anneal procedure. Longer field-anneals result in larger time constants and seem to induce a hurdle that prevents complete alignment at low temperatures and/or for small fields. Results indicate the molten composite is a non-Newtonian fluid that can support a yielding stress. Scanning Electron microscopy (SEM) images taken on field-annealed samples at 230 °C show strong chaining with little PA-12 left between individual Sr-ferrite particles suggesting that direct particle to particle interaction is the reason for the observed non-zero yielding stress. The melt viscosity of the composite increases with the number of thermal cycles above the melting temperature (Tm). Room temperature (RT) torque magnetometry measurements show that magnetic anisotropy depends on the field annealing process through induced shape anisotropy contributions originating from magnetic particle agglomerates.

Anisotropy of the Paramagnetic Susceptibility in the 3D Dirac Semimetal Cd-=SUB=-3-=/SUB=-As-=SUB=-2-=/SUB=- Caused by Chromium Impurity: the EPR on Cr-=SUP=-3+-=/SUP=- Ions

In the literature devoted to magnetic impurities in Dirac semimetals, the appearance of anisotropic and long-range non-oscillating contributions to the Ruderman--Kittel--Kasuya--Yosida interaction is predicted. These contributions are due to the hybridization of the wave functions of magnetic impurities with the wave functions of Dirac electrons, which have a linear dispersion law. We have studied electron paramagnetic resonance (EPR) in powder samples of topological 3D Dirac semimetal Cd3As2 with an admixture of chromium ions. Anisotropy of the magnetic susceptibility in the paramagnetic state was found from the behavior of the resonance field. The appearance of magnetic anisotropy in the paramagnetic state is associated with an increase in the contribution of the orbital moments of chromium ions Cr2+ and Cr3+ due to their interaction with the orbital moments of donor Dirac electrons, which have anomalously large values of g factors. Keywords: magnetic resonance, topological materials, magnetic impurities.