Magnetocrystalline Anisotropy Research Articles

Mechanical behavior of supersonic fine particle bombardment single crystal γ-TiAl alloys based on atomistic simulation: Effects of velocity and crystal plane

Abstract The crystal orientation significantly affects the plastic deformation and mechanical properties of γ-TiAl alloys. However, there are few studies on the mechanical behavior of supersonic fine particle bombardment of single-crystal γ-TiAl alloys impacted with different crystal planes and velocities at the nanoscale. And the characterization of the mechanical properties in the presence of dislocation defects after impact is lacked. Therefore, in this paper, molecular dynamics is used to simulate the impact response and post-impact mechanical response of supersonic fine particle bombardment single-crystal γ-TiAl alloy. The results show that: at a certain impact velocity, the different ways of inducing dislocation slip due to the number of slip system initiations under crystal anisotropy lead to a smaller depth of subsurface damage on the (001) crystallographic plane compared to the other crystallographic planes; moreover, the yield strength and Young's modulus of the (111) and (11 ̅0) crystallographic planes are the largest after the impact, respectively. Under the same crystal plane, the subsurface damage depths of all crystal planes decrease with the increase of impact velocity; the yield strength of the (111) crystal plane of γ-TiAl alloy gradually increases, the yield strength of the (001) and (11 ̅0) crystal planes decreases, and the modulus of elasticity of the (001) and (111) crystal planes after impact is less sensitive to velocity. The angle between the two slip surfaces formed by the L-C dislocation during impact is 70.24°, while the angle between the two slip surfaces formed by the Hirth dislocation is 109.76°. This will provide atomic-scale deformation details of the plastic deformation and mechanical response of single-crystal γ-TiAl alloys bombarded by supersonic fine particles.

Severe plastic deformation of Mn-Al permanent magnets

Manganese-aluminum permanent magnets are promising candidates to fill the cost and performance gap between lower-performance bonded ferrites and high-performance magnets based on rare-earth elements. This is due to the favorable combination of saturation magnetization and magnetocrystalline anisotropy in the Mn-Al τ phase combined with low raw material cost. However, the τ phase is metastable and prone to decomposition at high temperatures, making processing by conventional milling and sintering difficult. Severe plastic deformation (SPD) is an alternative processing route to control the microstructure of a material by applying very high amounts of strain. In this study, equal-channel angular extrusion (ECAE) and high-speed high-pressure torsion (HS-HPT) were both tested as SPD processing routes. ECAE improved magnetic energy product, (BH)max, by 220% by refining the grain size and imparting a high density of dislocations. HS-HPT enabled a rapid phase transformation from the high-temperature ε phase to the τ phase but lowered Hci, making it better suited to soft magnet processing.

Magnetocrystalline anisotropy and giant spontaneous magnetostriction in iron selenide Fe3Se4 studied on single crystals

Using the modified Bridgman method, a single-crystalline sample of iron selenide Fe3Se4 was grown and its magnetization and thermal expansion behavior was studied along different crystallographic directions. In a ferrimagnetically ordered state below TN = 345 K, the magnetization curves show that the magnetic moments do not lie strictly in the plane perpendicular to the c axis. The magnetocrystalline anisotropy constants, determined from the M(H) dependences along and across to the c axis, are K1 = −3.9⋅107 erg/cm3, K2 = 5.0⋅106 erg/cm3 at 4 K. Magnetic ordering in Fe3Se4 upon cooling below TN is accompanied by anisotropic deformations of the crystal lattice: expansion along the c axis and compression across the c axis. Spontaneous volume magnetostriction is positive and reaches a giant value of about 1.2⋅10-2 at 80 K. The pressure derivative of the Néel temperature is estimated using the Ehrenfest ratio as of dTN/dp ≈ − 2.1 K/kbar. The results obtained show that the properties of Fe3Se4 are strongly influenced by magnetoelastic interactions.

Generation of Entanglement and Perfect One‐Way EPR Steering via Kerr Nonlinearity in Cavity Magnonics System

AbstractA scheme is proposed for generating entanglement and achieving perfect one‐way EPR (Einstein–Podolsky–Rosen) steering in a cross‐shaped cavity magnonics system via the Kerr effect arising from magnetocrystalline anisotropy. The scheme involves two microwave cavities with distinct quality factors that simultaneously couple to a magnon mode of a macroscopic yttrium‐iron‐garnet sphere via the magnetic‐dipole interaction. It is demonstrated that both the bipartite and tripartite entanglement among the three modes will be generated due to Kerr nonlinearity, and the perfect one‐way EPR steering will also be achieved between the cavity with higher quality factor and the magnon mode. Notably, this scheme differs from conventional protocols that produce asymmetric EPR steering by introducing additional unbalanced losses or noises; instead, it can generate and manipulate one‐way EPR steering solely by adjusting the detuning between the magnon mode and the microwave drive field. It is also analyzed that the robustness of the entanglement and EPR steering against the dissipation of magnon and environmental temperature. The present scheme may provide a promising platform and an efficient quantum resource for quantum information processing.

High-performance multiphase Sm-Co-B alloys with coercivities up to 6.71 MA·m−1

SmCo4B-based alloys with high magnetocrystalline anisotropy are expected to be used as raw materials or constituent phases for new permanent magnets. In this work, we develop Sm(Co, Fe, Ni)4B alloys with excellent hard magnetic properties by tuning the contents of Fe, Co, and Ni. The addition of Fe enhances the amorphous formation ability of the as-spun ribbons, whereas Ni addition improves the structural stability of the crystalline phases. During annealing, the amorphous phase crystallizes into different Sm-Co-B phases in stages. A high coercivity of 5.68–6.71 MA·m−1 is obtained in the annealed SmCo4–x–yFexNiyB (x = 1.0–2.0, y = 0.8–1.0) ribbons composed of platelet-shaped and equiaxed grains in comparison with the coercivity of 2.89–5.18 MA·m−1 in the x = 1.0–1.2 and y = 0–0.8 ribbons with equiaxed grains. Here, we show the strong correlations between the microstructure and magnetic properties and provide insights for the future development of high-performance SmCo4B-based magnets.

Topological Hall effect instigated in kagome Mn3–xSn due to Mn-deficit induced noncoplanar spin structure

Magnetic topological semimetals are manifestations of the interplay between electronic and magnetic phases of matter, leading to peculiar characteristics such as the anomalous Hall effect (AHE) and the topological Hall effect (THE). Mn3Sn is a time-reversal symmetry-broken magnetic Weyl semimetal showing topological characteristics within the Kagome lattice network. This study reveals a large THE in Mn2.8Sn (6% Mn deficit Mn3Sn) at room temperature in thexy-plane, despite being an antiferromagnet. We argue that the magnetocrystalline anisotropy induced noncoplanar spin structure is responsible for the observed THE in these systems. Further, the topological properties of these systems are highly anisotropic, as we observe a large AHE in thezx-plane. We find that Fe doping at the Mn site, Mn3-xFexSn (x= 0.2, 0.25, & 0.35), tunes the topological properties of these systems. These findings promise the realization of potential topotronic applications at room temperature.

Current-induced resonance in long conductive ferromagnetic nano-wires

Ferromagnetic nanowires are receiving attention as functional elements in technologically important applications in microwave devices, spintronics, and biomedicine. They can be readily fabricated over large areas using electrodeposition, and their magnetic response can be tuned through control of their size, geometry, and composition. Additionally, their geometrical properties provide a stable spin structure for manipulating magnetization dynamics using spin-polarized currents for spintronic applications. Structural analysis of individual cobalt nanowires indicated magnetocrystalline anisotropy predominantly perpendicular to the nanowire axis. This significantly alters the micromagnetic energy landscape in the nanowire and breaks the circular symmetry of the dynamic magnetization and resonance modes which is often assumed in theory. In this article, we investigate, using finite-element micromagnetic–electromagnetic simulations, the effect of the variation of magnetocrystalline anisotropy angle on the dynamic magnetization in the nanowire and leads to a shift in the resonance frequencies and modes. The resonance is induced by a pulsed electric current applied along the nanowire axis and simulations include the contributions of magnetocrystalline anisotropy, exchange, dipolar fields, and eddy currents. Understanding the magnetization dynamics induced by electric currents and spin-wave modes in metallic magnetic nanowires and their size and anisotropy angle dependence is important for the design and tuning of magnetic nanowire arrays and devices.

Shock compression behavior and dynamic strength properties of preheated tantalum: Role of crystal anisotropy

Shock compression behavior and dynamic strength properties of preheated tantalum: Role of crystal anisotropy

Relationship between orbital moment anisotropy, magnetocrystalline anisotropy, and Dzyaloshinskii-Moriya interaction in W/Co/Pt trilayers

We have studied the Co layer thickness dependences of magnetocrystalline anisotropy (MCA), Dzyaloshinskii-Moriya interaction (DMI), and orbital moment anisotropy (OMA) in W/Co/Pt trilayers, in order to clarify their correlations with each other. We find that the MCA favors magnetization along the film normal and monotonically increases with decreasing effective magnetic layer thickness (teff). The magnitude of the Dzyaloshinskii-Moriya exchange constant (|D|) increases with decreasing teff until teff∼1 nm, below which |D| decreases. The MCA and |D| scale with 1/teff for teff larger than ∼1 nm, indicating an interfacial origin. The increase of MCA with decreasing teff continues below teff∼ 1 nm, but with a slower rate. To clarify the cause of the teff dependences of MCA and DMI, the OMA of Co in W/Co/Pt trilayers is studied using x-ray magnetic circular dichroism. We find nonzero OMA when teff is smaller than ∼0.8 nm. The OMA increases with decreasing teff more rapidly than what is expected from the MCA, indicating that factors other than OMA contribute to the MCA at small teff. The teff dependence of the OMA also suggests that |D| at teff smaller than ∼1 nm is not related to the OMA at the interface. We propose that the growth of Co on W results in a strain and/or texture that reduces the interfacial DMI, and, to some extent, MCA at small teff. Published by the American Physical Society 2024

Metallic Ca Aggregates Formed Along Ion Tracks and Optical Anisotropy in CaF2 Crystals Irradiated with Swift Heavy Ions

It is known that swift heavy ion (SHI) irradiation induces the shape elongation of metal nanoparticles (NPs) embedded in transparent insulators, which results in anisotropic optical absorption. Here, we report another type of the optical anisotropy induced in CaF2 crystals without including intentionally embedded metal NPs. The CaF2 samples were irradiated with 200 MeV Xe14+ ions with an incident angle of 45° from the surface normal. With the increasing fluence, an absorption band at ~550 nm, which is ascribed to Ca aggregates, increases both the intensity and the anisotropy. XTEM observation clarified the formation of the continuous line structures and the discontinuous NP chains parallel to the SHI beam. Numerical simulations of the optical absorption spectra suggested the NP chains but not the continuous line structures as the origin of the anisotropy. The optical anisotropy in CaF2 irradiated with SHIs is different from the shape elongation of NPs.

Annealing-induced changes in Sol-Gel synthesized nano-CoFe2O4: A study of structure, morphology and magnetism

Magnetic nano-sized CoFe₂O₄ spinel ferrites were synthesized using the sol-gel auto-combustion technique, and the impact of annealing temperature on their structural and magnetic properties was systematically studied. Samples were annealed at 500 °C, 700 °C, and 900 °C for 5 hours. XRD analysis confirmed crystallization in the Fd3m space group, with average crystallite sizes ranging from 30 to 34 nm. Structural parameters such as ionic radii, bond lengths, and cation distribution were also calculated, revealing partial inversion with an inversion factor of 0.68. FE-SEM analysis showed uniform morphology and increasing grain size with higher annealing temperatures. EDS confirmed stoichiometric Co and Fe ion content, while FTIR indicated strong metal-oxide bonds characteristic of CoFe₂O₄. Magnetic measurements demonstrated that higher annealing temperatures enhanced saturation magnetization and magnetocrystalline anisotropy while reducing coercivity, highlighting the significant influence of annealing temperature on CoFe₂O₄ nanoparticles' performance.

Magnetocrystalline anisotropy energy of AYbO3 (A= Sr, Ba and Ca) perovskite oxides

First-principles calculations and Monte Carlo simulations were employed to explore the effect of magnetic anisotropy on magnetocaloric properties and the magnetocrystalline anisotropy energy (MAE) of AYbO3 (A = Sr, Ba and Ca) perovskite oxides. The equilibrium lattice constant a0 is calculated AYbO3 (A = Sr, Ba and Ca). The elastic constants and related mechanical quantities such as bulk modulus B, Zener anisotropy factor A and Cauchy pressure Cp were calculated. CaYbO3 and SrYbO3 exhibit the half-metallic characteristic. While BaYbO3 exhibits semiconductor character. Sr, Ba and Ca atoms located in the A site affected the values of magnetocrystalline anisotropy energy (MAE) so changing the sign of the magnetic anisotropy constant in SrYbO3. The magnetic anisotropy shows that the easy axis is along the axis [100] for SrYbO3, CaYbO3 and BaYbO3 respectively. The critical temperature around Tc = 65 K using the MCS method. The isothermal magnetic entropy change was calculated for BaYbO3 under different magnetic fields and magnetic anisotropy. The highest isothermal entropy change obtained at H = 5T and D = 0 is 5.51 J/kg.K. While it’s equal to 8.10 J/kg.T at H = 5T and D =5.

Pr-modified microstructure enhances coercivity in Sm2Co17-type magnets

Optimizing components of the cellular structure is a strategy to enhance the magnetic performance of Sm2Co17-type magnets. In this study, Pr is used to modify the cellular structure in Sm2Co17-type magnets, achieving synergistic optimization of coercivity from 32.12 kOe to 34.71 kOe and remanence from 11.23 kGs to 11.36 kGs. Analyses reveal that the increased remanence is attributed to the enhanced saturation magnetization and better grain alignment in the Pr-5 magnet. The incomplete cellular structures and Cu-lean region near grain boundaries are ameliorated in the Pr-5 magnets. Meanwhile, the Pr-modified and Cu-enriched cellular boundary phase, which has a lower magnetocrystalline anisotropy field, enhances the pinning strength of the domain-wall and contributes to the increase in coercivity. The substitution of Pr for Sm has a lower substitution energy in SmCo5 than in Sm2Co17, leading to the slight enrichment of Pr in the 1:5H phase. However, excessive Pr leads to increased amounts of oxides and deteriorates magnetic properties. This work provides valuable insights into developing high-performance Sm2Co17-type magnets by optimizing the microstructure and microchemical components.

Intrinsic Magnetocrystalline Anisotropy Induced 3m-Symmetry Dependent Field-Free Switching in Epitaxial Garnet Films.

The electrical control of perpendicular magnetization without the need for external magnetic fields holds significant potential for next-generation spintronic devices. In this Letter, we have identified a 3m-symmetry dependent field-free switching phenomenon in (111)-oriented Tm_{3}Fe_{5}O_{12} single-crystal films capped with a platinum (Pt) layer. We demonstrate that this distinctive property arises due to the spontaneous breaking of mirror symmetry in magnetocrystalline anisotropy (MCA) for (111)-oriented magnetic films with a cubic structure, which results in a local out-of-plane MCA effective field with a 3m-symmetry dependence on the azimuth angle when the magnetization lies in the (111) plane. The observed field-free switching, facilitated by this MCA effective field, is validated by numerical simulations based both on macro-spin model and on micromagnetic theory. Our findings not only underscore the instrumental role of intrinsic MCA in enabling field-free magnetization switching but also enrich the fundamental understanding of the underlying switching dynamics.

Giant Uniaxial Magnetocrystalline Anisotropy in SmCrGe3.

Magnetic anisotropy is a crucial characteristic for enhancing the spintronic device performance. The synthesis of SmCrGe3 single crystals through a high-temperature solution method has led to the determination of uniaxial magnetocrystalline anisotropy. Phase verification was achieved by using scanning transmission electron microscopy (STEM), powder, and single-crystal X-ray diffraction techniques. Electrical transport and specific heat measurements indicate a Curie temperature (TC) of approximately 160 K, while magnetization measurements were utilized to determine the anisotropy fields and constants. Curie-Weiss fitting applied to magnetization data suggests the contribution of both Sm and Cr in the paramagnetic phase. Additionally, density functional theory (DFT) calculations explored the electronic structures and magnetic properties of SmCrGe3, revealing a significant easy-axis single-ion Sm magnetocrystalline anisotropy of 16 meV/fu. Based on the magnetization measurements, easy-axis magnetocrystalline anisotropy at 20 K is 13 meV/fu.

Importance of magnetic shape anisotropy in determining triaxial magnetic anisotropy of ferromagnetic semiconductor CrSCl monolayer

Abstract Magnetic anisotropy (MA) is pivotal for stabilizing long-range magnetic order in two-dimensional (2D) systems against thermal fluctuations. Here, we conduct a comprehensive investigation of the electronic and magnetic properties of CrSCl monolayer using first-principles methods and Monte Carlo (MC) simulations. Our results reveal that CrSCl monolayer exhibit a direct band gap ferromagnetic semiconductor (FMS) with a high Curie temperature (TC, 143 K). Notably, we identify triaxial magnetic anisotropy in this monolayer, characterized by the easy magnetization axis along the y-axis, intermediate axis along the x-axis, and hard axis along the z-axis. This anisotropy arises from a combination of magnetocrystalline anisotropy and shape anisotropy, in which shape anisotropy dominating over weak magnetocrystalline anisotropy. Orbital projection analysis shows that the major contribution of magnetic anisotropy energy comes from the d orbital of Cr atom. These findings provide some insights into the strain response of MA and suggest that studies of other FM monolayers may uncover future contenders for strain-switchable and ultra-compact spintronics devices.

The magnetocrystalline anisotropy of Y2(FexCo1-x)17Hy compounds

The article presents the results of magnetocrystalline anisotropy (MCA) investigation of Y2(FexCo1-x)17 (x = 0.03–0.50) rare-earth quasi-binary bulk crystal samples and their hydrides. The specific magnetization curves m(H) were measured in the wide temperature range for the original Y2(FexCo1-x)17 samples and for the corresponding hydrides. Magnetocrystalline anisotropy constants K1, K2 were calculated, temperature and compositional dependence curves were plotted based on m(H) data. The temperature dependences of specific saturation magnetization ms(T) and first anisotropy constant K1(T) were analyzed to determine temperature behavior patterns, estimate the Curie temperature Tc and predict the spin-reorientation transitions. The first anisotropy constant, saturation magnetization and Curie temperature compositional dependences of original Y2(FexCo1-x)17 and hydrogenated Y2(FexCo1-x)17Hy samples were compared to identify the hydrogenation effect on the magnetic properties of investigated compounds. The revealed patterns were explained in terms of the crystal structure of the compounds.

Study of the influence of nitrogen doping on magnetic anisotropy in CoFe/MgO thin films with different deposition sequences

Abstract The ferromagnetic (FM)/MgO structure multilayers with perpendicular magnetic anisotropy (PMA) play a crucial role in magnetic random-access memory. It is essential to explore the methods for modulating magnetic anisotropy and to clarify the underlying mechanisms. We study the regulation of the magnetic anisotropy with nitrogen (N) doping concentration (CN) in two samples: Ta/CoFe(N)/MgO/Ta (S1) and Ta/MgO/CoFe(N)/Ta (S2) with different deposition sequences. The S1 sample exhibits in-plane magnetic anisotropy (IMA) without N doping. And the sample presents PMA when CN = 15%. The S2 sample shows weak PMA without N doping, and the sample converts to IMA when CN = 15%. X-ray photoelectron spectroscopy is performed to evaluate the oxidation level of Fe at the CoFe/MgO interface by the peak area ratio of Fe oxide to Fe (ϵ). It is believed that excessively high and low ϵ values correspond to over-oxidation and under-oxidation of Fe, respectively. For films deposited in different sequences, both over-oxidation and under-oxidation lead to IMA, while moderate oxidation facilitates the formation of PMA. The microstructure analysis reveals that the N doping does not affect the crystallization of the films, indicating that magnetocrystalline anisotropy has a minor influence on the changes of K eff.

Origin of magnetism via cation vacancy defects in non-stoichiometric NiCo2O4 nanoparticles: A synchrotron-based x-ray absorption and x-ray magnetic circular dichroism spectroscopic study

The present study probes the effect of cation distributions in the structural, optical, electronic, and magnetic properties of mixed-valent inverse-spinel NiCo2O4 (NCO) nanoparticles (NPs). NCO NPs were prepared using the sol–gel combustion method and the grain size was obtained in the magnetic exchange length range assumed to be from single-ion anisotropy. The Raman and photoluminescence spectroscopies confirm the presence of an inverse-spinel structure with different oxidation states, and vibrating sample magnetometry clarifies the existence of ferromagnetism with the presence of magnetic anisotropy among the cations. These NPs annealed at a higher grain-growth temperature accumulate ferrimagnetic properties and produce magneto-crystalline anisotropy making NCO an assuring material for spintronic applications. A detailed x-ray absorption spectroscopy and x-ray magnetic circular dichroism studies reveal an indestructible correlation between the distribution of the present cations and the element-specific origin of ferrimagnetic behavior. Ni is found to be accountable for the magnetic moment and electronic conduction, whereas Co is associated mainly with the generation of the magnetic anisotropy even in the polycrystalline NP form. This describes the anti-ferromagnetic coupling between Co and Ni ions that is pivotal in demonstrating the exchange interaction between these cations. The above result signifies the site-dependent cation valence states for the magnetic properties, and the extent of growing conditions are related to such cation-site dysfunction. This depicts further tunability in NCO as a functional oxide material.

Tunning Pr to achieve ultra-high magnetic properties of anisotropic nanocrystalline (Sm,Pr)Co5 magnets

In this study, we reported on the bulk anisotropic nanocrystalline Sm1-xPrxCo5 (x = 0.2–0.6) magnets aimed at achieving excellent energy products. Through a combination of advanced processing techniques, including melt spinning, hot pressing, and hot deformation process, bulk magnets with a fine nanocrystalline structure were successfully synthesized. The results revealed that the substitution of Pr strengthened the c-axis texture and the saturation magnetization, facilitating the enhancement of remanence (Mr) and maximum magnetic energy product [(BH)max]. However, Pr substitution decreased the coercivity (Hci) due to the reduced magnetocrystalline anisotropy field. Excellent magnetic properties are obtained for Sm0.4Pr0.6Co5 magnets with the (BH)max of 23.2 MGOe and Hci of 11.8 kOe. The prepared (Sm,Pr)Co5 magnets with different Pr contents have essentially the same microstructure with RECo5 main phase grains of about 400 nm in diameter and fine dispersed rare earth-rich nanoprecipitates. Our findings can provide reliable reference for manufacturing nanocrystalline permanent magnet materials and promote the development of rare earth permanent magnet new materials.