Crystalline Anisotropy Research Articles

Structural, thermodynamic, and magnetic properties of SrFe12O19 hexaferrite modified by co-substitution of Cu and Gd.

A hard magnetic system of SrFe12O19 nanomaterial was modified according to the composition of Sr0.95Gd0.05Fe12-xCuxO19 with x = 0.0, 0.30, and 0.60 using the sol-gel technique. The structures of the samples were evaluated using X-ray diffraction (XRD) along with Rietveld refinement, and an M-type hexaferrite with a hexagonal structure was confirmed with a trace amount of the α-Fe2O3 phase. In addition, transmission electron microscopy (TEM) analysis revealed polycrystalline nanoplates in all samples. Furthermore, the bond structures of the octahedral and tetrahedral sites along with the thermodynamic properties of these ferrites were extracted from the FTIR spectra at room temperature. The Debye temperature (θD) decreased from 755.9 K to 749.3 K due to the co-substitution of Gd3+ at Sr2+ and Cu2+ at Fe3+. The magnetic hysteresis (M-H) measurements revealed that the coercivity decreased from 5.3 kOe to 1.5 kOe along with the highest magnetization saturation (Ms) of 65.2 emu g-1 for the composition Sr0.95Gd0.05Fe11.7Cu0.3O19, which is suitable for industrial application. The effect of local crystalline anisotropy in magnetization was explored using the law of approach to saturation (LAS). Finally, thermo-magnetization was recorded in the range from 400 K to 5 K for cooling under zero field and in the presence of a 100 Oe field, and magnetic transitions were tracked due to the introduction of the foreign atoms of Gd and Cu into SrFe12O19.

Study on the relationship between structure and magnetic properties of τ-phase MnAl prepared by cryo-milling

The unique characteristics, such as high magnetic moment, high Curie temperature, large magnetic crystalline anisotropy, and low cost, make the τ-phase MnAl a promising candidate as the market alternatives which could fill the gap between the rare earth magnets and ferrite magnets. Because at low temperatures the metal will become more brittle, the cryomilling technology may allow the τ-phase MnAl to be broken quickly and introduce few crystal defects, and then obtain better permanent magnetic properties. In this study, the cryomilling technology was used to grind the τ-phase MnAl, and the structural and magnetic properties of the obtained powder sample were investigated. It was found that compared to room-temperature ball milling, the morphology of cryomilled powders is granular and the powder agglomeration is dramatically suppressed at a low temperature, and as a result the larger particles tend to be broken down into smaller ones rather than being agglomerated to larger thin layers. The grain size D reduced continuously from 145 nm to 36 nm when the sample was milled for 120 minutes. The coercivity increased with increasing the cryo-milling time, while the saturation magnetization decreased. The maximum coercivity of up to 4.9 kOe was obtained by cryo-milling for 100 minutes. By the neutron diffraction analysis, it was confirmed that the decrease of the saturation magnetization with increasing milling time is mainly due to the migration of Mn atoms from 1a site to the 1d site and the decrease of Mn atomic magnetic moment.

Re/Ir@Os-doping induced insulator-to-metal transition in Mott-insulator Ca2FeOsO6: octahedral distortion effects.

Regardless of several investigations to elucidate the ground state of the strongly correlated electron systems in doped Mott-insulators (MIs), the origin of the doping-induced insulator-to-metal transition (IMT) remains a crucial and debatable subject in solid-state physics. Herein, we explore the consequences of Re/Ir-doping at the Os-site (Re/Ir@Os), on the physical properties of the MI ferrimagnetic (FiM) Ca2FeOsO6 double perovskite oxides using density functional theory calculations. The doped structures' solidity is analyzed by computing the defect formation energies in terms of the dopant-rich situation, which confirms their growth credibility at ambient conditions along with mechanical and dynamical stabilities. Various FiM spin-ordering is taken into account in the doped structures to analyze the magnetic ground state, which is FiM-I/FiM-II in the Re/Ir@Os-doped system. Remarkably, an IMT is predicted in the Re/Ir@Os-doped structures, which is due to the admixture of the partially occupied 5d orbitals of these ions. The calculated partial spin magnetic moments (ms) of +4.12, -1.58, -0.75 and +0.88μB on the Fe, Os, Re, and Ir ions, endorse the +3, +5, +5, and +4 states having electronic configurations of t32g↑t02g↓e2g↑e0g↓, t32g↑t02g↓e0g↑e0g↓, t22g↑t02g↓e0g↑e0g↓, t32g↑t22g↓e0g↑e0g↓, respectively. The "+" and "-" signs on the ions ms values, lead the systems into various FiM magnetic ordering. Moreover, the estimated Curie temperature (TC) using the Heisenberg model in the pristine structure is 334 K, which is close to the experimentally observed value of 320 K along with a colossal uniaxial magneto crystalline anisotropy energy constant (K) of 2.95 × 107 erg cm-3 having the easy magnetic axis of the ac-plane ([101]). It is established that TC/K reduces and enhances to 298 K/1.33 × 107 erg cm-3 and 365 K/4.71 × 107 erg cm-3 for the Re@Os and Ir@Os-doped motif due to an increase and decrease in the octahedral distortions compared to that of the pristine system, respectively.

Crystalline Magnetic Anisotropy in High Entropy (Fe, Co, Ni, Cr, Mn)3O4 Oxide Driven by Single‐Element Orbital Anisotropy

AbstractThe design of multicomponent materials has captured considerable attention due to its extraordinary ability to tailor functional properties. However, how a single element affects the behavior of the overall material has yet to be explored in depth. In this study, the heteroepitaxy of high entropy (Fe, Co, Ni, Cr, Mn)3O4 films with varying strain states are investigated in magnetic performance. It is discovered that the high entropy oxide thin film with compressive strain exhibits an effect of crystalline magnetic anisotropy. Diverse analyses provide a detailed understanding of high entropy magnetic oxide systems, including X‐ray diffraction, reciprocal space mapping, macroscopic magnetic characterization, X‐ray absorption spectroscopy (XAS), etc. Notably, the element‐specific XAS technique proves effective in uncovering the origin of the crystalline magnetic anisotropy. Due to the substrate‐induced epitaxial strain, the eg orbitals of Mn3+ form different energy levels, leading to different preferred electron occupancy. The exploration of magnetic properties in epitaxial high entropy oxide film is then raveled. By navigating the complexities introduced by the random atom distribution and intricate magnetic interactions, this study pioneers novel methodologies for probing the core physics of high entropy oxides.

Computational Discovery of High-Temperature Ferromagnetic Semiconductor Monolayer H-MnN2.

In the past few years, two-dimensional (2D) high-temperature ferromagnetic semiconductor (FMS) materials with novelty and excellent properties have attracted much attention due to their potential in spintronics applications. In this work, using first-principles calculations, we predict that the H-MnN2 monolayer with the H-MoS2-type structure is a stable intrinsic FMS with an indirect band gap of 0.79 eV and a high Curie temperature (Tc) of 380 K. The monolayer also has a considerable in-plane magnetic anisotropy energy (IMAE) of 1005.70 μeV/atom, including a magnetic shape anisotropy energy induced by the dipole-dipole interaction (shape-MAE) of 168.37 μeV/atom and a magnetic crystalline anisotropy energy resulting from spin-orbit coupling (SOC-MAE) of 837.33 μeV/atom. Further, based on the second-order perturbation theory, its in-plane SOC-MAE of 837.33 μeV/atom is revealed to mainly derive from the couplings of Mn-dxz,dyz and Mn-dx2-y2,dxy orbitals through Lz in the same spin channel. In addition, the biaxial strain and carrier doping can effectively tune the monolayer's magnetic and electronic properties. Such as, under the hole and few electrons doping, the transition from semiconductor to half-metal can be realized, and its Tc can go up to 520 and 620 K under 5% tensile strain and 0.3 hole doping, respectively. Therefore, our research will provide a new, promising 2D FMS for spintronics devices.

Observation of itinerant ferromagnetic behaviour in equiatomic medium entropy AlNiCo alloy

A medium entropy AlNiCo alloy has been synthesized by vacuum arc melting, which shows single phase B2 structure. Atom probe tomography analysis showed that the elements are homogeneously and randomly distributed in AlNiCo alloy without any clustering tendency. A detailed analysis of temperature and field dependent magnetization data suggests an itinerant ferromagnetic ground state of AlNiCo alloy. The magneto crystalline anisotropy is evaluated to be 1.03 × 105 ergs/cm3 at 5 K. A broad maximum at low temperature in zero-field-cooled (ZFC) magnetization, as well as irreversibility of ZFC and field-cooled (FC) curves indicated a glassy behavior. This observation is supported by the memory effects observed at low temperature. The observed anomalous magnetic behavior is discussed in terms of modifications in exchange interactions. To the best of our knowledge, this is the first report on microstructure and magnetic properties of an equiatomic ternary AlNiCo alloy.

Ultrahigh electrostrictive coefficient and hysteresis-free electrostrictive strain in textured BCZT ceramic

Precision-controlled systems necessitate electronic actuators with large displacement, high precision, and miniaturization. Therefore, advanced ferroelectric functional ceramic materials must exhibit substantial displacement responsiveness, minimal hysteresis, and performance stability. Modifying electrostrictive ceramics to enhance the electrostrictive coefficient (Q33) through conventional doping strategies has proven challenging. To address this, grain-oriented textured ceramics harness crystalline anisotropy to elevate Q33 and electrostrictive strain response. In this work, we employ the template grain growth (TGG) method integrating preprepared BaTiO3 (BT) microtemplates, to cultivate <001>-oriented 0.5Ba(Zr0.2Ti0.8)O3-0.5(Ba0.7Ca0.3)TiO3 (BCZT) ceramics. Remarkably, the <001>-oriented BCZT ceramic manifests a substantial Q33 value of 0.066 m4/C2, marking a 65 % increase compared to randomly oriented ceramics. Under 100 kV/cm, ultra-high electrostrictive strain response (0.23%) and minimal hysteresis (1−8%) were achieved. Crucially, this elevated Q33 remains thermally stable within the range of 20−100 °C. This advancement not only enables the production of electrostrictive ceramics with improved Q33 and hysteresis-free strain but also broadens the application horizon of BCZT-based electrostrictive ceramics within high-precision actuator technologies.

Sustainable Nanomagnetism: Investigating the Influence of Green Synthesis and pH on Iron Oxide Nanoparticles for Enhanced Biomedical Applications.

This study comprehensively analyzed green nanomagnetic iron oxide particles (GNMIOPs) synthesized using a green method, investigating their size, shape, crystallinity, aggregation, phase portions, stability, and magnetism. The influence of pH and washing solvents on the magnetic properties of the nanoparticles and their incorporation into PCL membranes was examined for biomedical applications. Polyphenols were utilized at different pH values (1.2, 7.5, and 12.5), with washing being performed using either ethanol or water. Characterization techniques, including XRD, SEM, TEM, FTIR, and VSM, were employed, along with evaluations of stability, magnetic properties, and antioxidant activity. The findings indicate that both pH levels and the washing process exert a substantial influence on several properties of NMIOPs. The particle sizes ranged from 6.6 to 23.5 nm, with the smallest size being observed for GNMIOPs prepared at pH 12.5. Higher pH values led to increased crystallinity, cubic Fe3O4 fractions, and reduced crystalline anisotropy. SEM and TEM analyses showed pH-dependent morphological variations, with increased aggregation being observed at lower pH values. GNMIOPs displayed exceptional magnetic behavior, with the highest saturation magnetization being observed in GNMIOPs prepared at pH 7.5 and 12.5 and subsequently washed with ethanol. The zeta potential measurements indicated a stability range for GNMIOPs spanning from -31.8 to -41.6 mV, while GNMIOPs synthesized under high-pH conditions demonstrated noteworthy antioxidant activity. Furthermore, it was explored how pH and washing solvent affected the morphology, roughness, and magnetic properties of GNMIOP-infused nanofiber membranes. SEM showed irregularities and roughness due to GNMIOPs, varying with pH and washing solvent. TEM confirmed better dispersion with ethanol washing. The magnetic response was stronger with ethanol-washed GNMIOPs, highlighting the influence of pH and washing solvent on membrane characteristics.

An Analytical Model of Light Scattering by Birefringent Polycrystalline Dielectrics Using Perturbation of Maxwell's Equations

AbstractPolycrystalline materials have shown promise in advanced optical applications because of their unique optical and mechanical properties. Most polycrystalline materials have non‐uniform optical properties due to residual porosity, secondary phases, and/or crystalline anisotropies (e.g., birefringence). These optical inhomogeneities manifest as scattering that reduces the transparency of the polycrystal. Even in the case of a single‐phase polycrystal with negligible porosity, birefringence scattering will always be present whenever the crystal is anisotropic (non‐cubic). Multiple models for predicting birefringence scattering have been suggested in the literature that are successful in describing scattering loss in specific material systems. Here a first‐principles model of birefringent scattering that is applicable to any single‐phase, unaligned transparent polycrystal is derived. The model can treat grain size distributions and is not limited to a specific material system. The derivation culminates in an equation that describes birefringence scattering coefficient spectra using the single‐crystal refractive index tensor and chord length distribution (measured from a representative polished surface micrograph). The model should be useful for designing materials and characterization. For example, it can be used to predict transmissions of transparent polycrystals for a range of grain sizes or to characterize the average grain size using a transmission measurement.

Electronic structure and magnetothermal property of two-dimensional ferromagnetic NbSe2 monolayer regulated by carrier concentration

Investigating high-performance and stable spintronics devices has been a research hotspot in recent years. In this paper, we employed first-principles methods and Monte Carlo (MC) simulations to explore the structure, electronic, and magnetic properties of monolayer NbSe2, as well as its behavior under carrier concentration modulation. The research on the electronic structure reveals that by introducing an appropriate amount of holes, the material can undergo a transition from metal to a half-metal state, achieving 100% high spin polarization. Investigation of magnetic crystalline anisotropy shows that the magnetic crystal anisotropy energy of 1210 μeV in out-of-plane is beneficial to maintain ferromagnetic order at high temperatures. In addition, doping with suitable carriers can effectively enhance or strengthen the ferromagnetic coupling in NbSe2 so that the magnetization easy axis is shifted. This reveals the potential application prospects of NbSe2 in electronically controlled spintronic devices. Analysis of the Fermi surface shows that both holes and electron doping increase the Fermi velocity of the material. The effect of hole doping is particularly significant, indicating its potential application in Fermi velocity engineering. Under the theoretical framework of the extended two-dimensional Ising model, based on MC simulation, the Curie temperature (TC) of NbSe2 is predicted to be 162 K. The effects of carrier concentration and the magnetic field on the magnetic and thermal properties of monolayer NbSe2 are simulated. The results show that appropriately increasing the hole doping concentration and magnetic field is conducive to obtaining ferromagnetic half-metallic materials with TC higher than room temperature, which provides theoretical support for experimental preparation.

Modeling the Anisotropic Transport Behavior for Axisymmetric 2D Electrode Particles Using a Modified Pseudo-2D Model Framework

This presentation extends widely used pseudo-2D (P2D) Li-ion battery models to include electrode particles that have strong crystal-scale anisotropies and possibly non-spherical shapes. Typical P2D models predict Li transport with representative spherical electrode particles by solving a one-dimensional diffusion equation in spherical coordinates. However, battery electrodes (graphite, NMC, etc.) may have strong crystalline anisotropies, leading to transport and mechanical properties that vary by orders of magnitude depending on crystallographic orientations. The anisotropic transport can cause large concentration gradients, possibly leading to particle fracture associated with concentration-induced stress. The remainder of the P2D model, such as Li-ion transport within the electrolyte solvent, remains essentially unchanged. The charge-transfer boundary conditions at the particle surfaces do need to accommodate the crystallographic anisotropy.The present model discretizes representative electrode particles in a two-dimensional finite-volume axisymmetric geometry, accounting for the anisotropic behaviors. The computational burden is greater than it is for the one-dimensional spherical solution. However, the P2D model with two-dimensional axisymmetric particle discretization still runs in only a few minutes on a typical personal computer.The model shows how electrode-particle anisotropy affects the battery performance, such as charge-discharge characteristics and electrochemical impedance spectroscopy. The model also predicts the concentration gradients and correlated stress for various axisymmetric, non-spherical particles.

Manipulating Skyrmion Motion on a Nanotrack with Varied Material Parameters and Tilted Spin Currents

Magnetic skyrmions are topological quasiparticles with nanoscale size and high mobility, which have potential applications in information storage and spintronic devices. The manipulation of skyrmion’s dynamics in the track is an important topic due to the skyrmion Hall effect, which can deviate the skyrmions from the preferred direction. We propose a new model based on the ferromagnetic skyrmion, where the skyrmion velocity can be well controlled by adjusting the direction of the current. Using this design, we can avoid the annihilation of the skyrmion induced by the skyrmion Hall effect, which is confirmed by our micromagnetic simulation based on Mumax3. In the meantime, we increase the average velocity of the skyrmion by varying the intrinsic material parameters in the track, where the simulations agree well with our analytical results based on the Thiele equation. Finally, we give a phase diagram of the output of the skyrmion in the T-type track, which provides some practical ways for design of logic gates by manipulating crystalline anisotropy through the electrical control.

Quantifying the Structure and Properties of Nanomagnetic Iron Oxide Particles for Enhanced Functionality through Chemical Synthesis.

This comprehensive study investigates the properties of chemical nanomagnetic iron oxide particles (CNMIOPs) synthesized through a chemical method. The primary objective is to examine how pH levels and washing solvents affect the magnetism properties of these nanoparticles. Three different pH levels (1.2, 7.5, and 12.5) using NaOH and two washing solvents (ethanol and water) are employed. The characterization techniques include FTIR, SEM, TEM, XRD, ZSP, and VSM. Furthermore, the study incorporates two specific pH- and solvent-dependent CNMIOPs into PCL electrospun materials to analyze their performance in a targeted application. The results show that pH and the washing process significantly affect the CNMIOPs' properties. Higher pH levels result in smaller particles with higher crystallinity and reduce crystalline anisotropy. SEM and TEM analysis confirm different morphologies, including cubic, spherical, and elongated shapes. Ethanol-washed CNMIOPs exhibit superior magnetic behavior, with the highest magnetization saturation at pH 12.5 (Ms = 58.3 emu/g). The stability of the CNMIOPs ranges from -14.7 to -23.8 mV, and higher pH levels exhibit promising antioxidant activity. Furthermore, the study explores the effects of pH and washing solvents on CNMIOP-infused nanofiber membranes, with better dispersion observed with ethanol washing. Overall, this research provides valuable insights into the properties and behavior of CNMIOPs under varying pH and washing conditions.

Evaluation of magnetic anisotropy in oriented plate-shaped strontium ferrite particles

Plate-shaped hexagonal SrFe12O19 particles, synthesized using potassium bromide as the molten salt flux, were dispersed in the resin using a planetary ball mill. Oriented sheets were prepared by coating the dispersion onto the films under a magnetic field. The coercive force and squareness ratio of the oriented sheets were 412 kA m−1 and 0.91, respectively. The magnetic anisotropy field was determined by measuring the rotational hysteresis losses of the oriented sheets with a magnetic torque meter. The anisotropy field was distributed in the range of approximately 200–1100 kA m−1, and particles with an anisotropy field of 478 kA m−1 comprised the majority. The magnetic anisotropy energy estimated from the magnetic anisotropy field was 104 KJ m−3. Assuming a reduction in the crystalline anisotropy field along the c-axis due to simply the shape anisotropy field resulting from the platelet shape of the particles, particles occupying the majority exhibited a maximum anisotropy field of 823 kA m−1.

Crystallographic texture effect on statistical microvoid growth in heterogeneous polycrystals

Polycrystalline materials usually exhibit obvious preferred grain orientations (i.e., crystallographic texture) after rolling and heat treatments, leading to a certain crystalline anisotropy. However, most previous studies on microvoid growth generally treated the material as homogeneous isotropic matrix, ignoring the influence of crystallographic texture. In the present work, four typical crystallographic textures of face-centered cubic crystal are considered, including the Cube, Goss, Brass and Copper textures. Afterwards, the texture effect on microvoid growth is systematically studied by crystal plasticity finite element simulation, from a statistical point of view. In addition, the role of loading mode (i.e., uniaxial or biaxial tension) in the texture effect on microvoid growth has also been explored. The results indicate that the crystallographic texture evidently affects the statistical void growth in heterogeneous polycrystals, regardless of the loading mode. Meanwhile, it has been found that the statistical void growth of Cube (resp. Brass) texture is always slower (resp. faster) than that of random grain-orientation case. Furthermore, it is interestingly concluded that for the four considered textures, the trend of statistical void growth (from fast to slow) is well consistent with that of average flow stress (from high to low) at any given strain level, which cannot be captured by the classical Rice-Tracey model. Finally, based on the statistical characteristics of void growth for different textures, a statistical Rice-Tracey model incorporating the texture effect is established. It is demonstrated that this statistical model can well envelop all the dispersed void growth results of different textures for the uniaxial tensile loading.

First-principles calculations to investigate structural, electronic and magnetic anisotropy energy of ZnFe[formula omitted]O[formula omitted] spinel ferrite for spintronics applications

Structural, electronic and magnetic investigations of ZnFe2O4 have been made by using density functional theory with Perdew–Burke–Ernzerhof Generalized-Gradient Approximation as exchange and correlation functional. Additionally, the effect of Hubbard, U, and spin orbit coupling, SOC on electronic and magnetic properties has also been observed. The U-value for Zinc and Iron are used, 6.0 eV (0.44 Ry) and 4.3 eV (0.316 Ry) respectively. The optimized lattice parameter matches well with experimental with mere percentage difference of 0.039%. This optimized lattice constant is used for SCF calculations to calculate the above mentioned properties of zinc ferrite. It is found that zinc ferrite have high value of magnetic moments, 19.721μB, 20.003μB, and 19.580μB for PBE, PBE with Hubbard, and with spin orbit coupling respectively. The magneto crystalline anisotropy energy calculations confirm the utility of this material for spintronics device fabrication.

Synthesis of Single Crystals of ε-Iron and Direct Measurements of Its Elastic Constants.

Seismology finds that Earth's solid inner core behaves anisotropically. Interpretation of this requires a knowledge of crystalline elastic anisotropy of its constituents-the major phase being most likely ε-Fe, stable only under high pressure. Here, single crystals of this phase are synthesized, and its full elasticity tensor is measured between 15 and 33GPa at 300K. It is calculated under the same conditions, using the combination of density functional theory and dynamical mean field theory, which describes explicitly electronic correlation effects. The predictive power of this scheme is checked by comparison with measurements; it is then used to evaluate the crystalline anisotropy in ε-Fe under higher density. This anisotropy remains of the same amplitude up to densities typical of Earth's inner core.

Crystalline electric field and magnetic anisotropy in Dy-based icosahedral quasicrystal and approximant

Crystalline electric field and magnetic anisotropy in Dy-based icosahedral quasicrystal and approximant

Effect of surface energy anisotropy on hole growth in a single-crystalline thin film: A phase-field study

Prediction of the temporal evolution of a pre-existing hole on a solid-state thin film has important implications for self-organized nanoscale pattern formation. In this work, we employ a three-dimensional phase-field model to elucidate the mechanism of corner instability during capillary-driven hole growth in a single-crystalline free-standing thin film. We perform a systematic study to demonstrate the effect of crystalline anisotropy in surface energy, surface diffusivity, and film thickness on hole growth. Our simulations reveal that the instability during hole growth arises due to saturation of the rim height at the corner of the hole that is directly related to the arc length of the corner, specified by the anisotropy in surface energy. Our investigation further reveals the presence of a time-invariant shape of the corner with the onset of corner instability.

Emergence of net magnetization by magnetic field biased diffusion in antiferromagnetic L10 NiMn

NiMn is a collinear antiferromagnet with high magneto crystalline anisotropy ($K_2=-9.7\times10^5\;\text{J m}^{-3}$). Through magnetic annealing of NiMn with excess Ni, strongly pinned magnetic moments emerge due to an imbalance in the distribution of Ni in the antiferromagnetic Mn-sublattices. The results are explained with a model of magnetic-field-biased diffusion, supported by ab initio calculations. Another observation is the oxidation of Mn at the surface, causing an enrichment of Ni in the sub-surface region. This leads to an additional ferromagnetic response appearing in the magnetization measurements, which can be removed by surface polishing.