Enhancement Of Magnetic Anisotropy Research Articles

Electrostatic Gating of Spin Dynamics of a Quasi-2D Kagome Magnet.

Electrostatic gating has emerged as a powerful technique for tailoring the magnetic properties of two-dimensional (2D) magnets, offering exciting prospects including enhancement of magnetic anisotropy, boosting Curie temperature, and strengthening exchange coupling effects. Here, we focus on electrical control of the ferromagnetic resonance of the quasi-2D Kagome magnet Cu(1,3-bdc). By harnessing an electrostatic field through ionic liquid gating, significant shifts are observed in the ferromagnetic resonance field in both out-of-plane and in-plane measurements. Moreover, the effective magnetization and gyromagnetic ratios display voltage-dependent variations. A closer examination reveals that the voltage-induced changes can modulate magnetocrystalline anisotropy by several hundred gauss, while the impact on orbital magnetization remains relatively subtle. Density functional theory (DFT) calculations reveal varying d-orbital hybridizations at different voltages. This research unveils intricate physics within the Kagome lattice magnet and further underscores the potential of electrostatic manipulation in steering magnetism with promising implications for the development of spintronic devices.

Progress of magnetic anisotropy enhancement mechanism in high-performance La-Co co-substituted M-type ferrites

La-Co co-substituted M-type ferrite,first reported at the end of the 20th century,has garnered continuous attention from researchers worldwide,serving as the cornerstone for high-performance permanent magnet ferrites.The unquenched orbital moments of Co<sup>2+</sup> play a pivotal role in enhancing the uniaxial anisotropy of M-type ferrites.However,a comprehensive understanding of its microscopic mechanism remains elusive.In response to the escalating performance demands of ferrite materials,elucidating the mechanism behind magnetic anisotropy enhancement becomes imperative,alongside the quest for guiding principles facilitating the swift and cost-effective development of high-performance products.but its mechanism at the microscopic level has not been explained.This review encompasses a comprehensive analysis of various studies aimed at pinpointing the crystal sites of Co substitution within the lattice.These investigations including neutron diffraction,nuclear magnetic resonance,and Mössbauer spectroscopy delve into the fundamental origins underlying the enhancement of magnetic anisotropy,thereby furnishing valuable insights for material design strategies geared towards further augmenting the magnetic properties of permanent magnet ferrites.The exploration of Co-substitution sites has yielded noteworthy findings.Through meticulous examination and analysis,researchers have discerned the intricate interplay between Co ions and the lattice structure,shedding light on the mechanisms governing magnetic anisotropy enhancement.The current mainstream view is that Co ions tend to occupy more than one site,namely the 4<i>f</i><sub>1</sub>,12<i>k</i>,and 2<i>a</i> sites,all of which are located within the spinel lattice.However,there have also been differing viewpoints,indicating that further exploration is needed to uncover the primary controlling factors influencing Co occupancy.Notably,the identification of specific Co substitution sites,especially the spin-down tetrahedron 4<i>f</i><sub>1</sub>,has enabled targeted modifications,culminating in the fine-tuning of magnetic properties with remarkable precision.Furthermore,the reviewed studies underscore the pivotal role of crystallographic engineering in tailoring the magnetic characteristics of ferrite materials.By strategically manipulating Co substitution,researchers have harnessed the intrinsic properties of the lattice to amplify magnetic anisotropy,thereby unlocking new avenues for the advancement of permanent magnet ferrites.In conclusion,the collective findings outlined in this review herald a promising trajectory for the field of permanent magnet ferrites.Armed with a nuanced understanding of Co-substitution mechanisms,researchers are poised to chart novel pathways toward the development of next-generation ferrite materials boasting enhanced magnetic properties.

Room-temperature-persistent magnetic interaction between coordination complexes and nanoparticles in maghemite-based nanohybrids.

Maghemite nanoparticles functionalised with Co(II) coordination complexes at their surface show a significant increase of their magnetic anisotropy, leading to a doubling of the blocking temperature and a sixfold increase of the coercive field. Magnetometric studies suggest an enhancement that is not related to surface disordering, and point to a molecular effect involving magnetic exchange interactions mediated by the oxygen atoms at the interface as its source. Field- and temperature-dependent X-ray absorption spectroscopy (XAS) and X-ray magnetic circular dichroism (XMCD) studies show that the magnetic anisotropy enhancement is not limited to surface atoms and involves the core of the nanoparticle. These studies also point to a mechanism driven by anisotropic exchange and confirm the strength of the magnetic exchange interactions. The coupling between the complex and the nanoparticle persists at room temperature. Simulations based on the XMCD data give an effective exchange field value through the oxido coordination bridge between the Co(II) complex and the nanoparticle that is comparable to the exchange field between iron ions in bulk maghemite. Further evidence of the effectiveness of the oxido coordination bridge in mediating the magnetic interaction at the interface is given with the Ni(II) analog to the Co(II) surface-functionalised nanoparticles. A substrate-induced magnetic response is observed for the Ni(II) complexes, up to room temperature.

Multi-Technique Experimental Benchmarking of the Local Magnetic Anisotropy of a Cobalt(II) Single-Ion Magnet.

A comprehensive understanding of the ligand field and its influence on the degeneracy and population of d-orbitals in a specific coordination environment are crucial for the rational design and enhancement of magnetic anisotropy of single-ion magnets (SIMs). Herein, we report the synthesis and comprehensive magnetic characterization of a highly anisotropic CoII SIM, [L2Co](TBA)2 (L is an N,N'-chelating oxanilido ligand), that is stable under ambient conditions. Dynamic magnetization measurements show that this SIM exhibits a large energy barrier to spin reversal U eff > 300 K and magnetic blocking up to 3.5 K, and the property is retained in a frozen solution. Low-temperature single-crystal synchrotron X-ray diffraction used to determine the experimental electron density gave access to Co d-orbital populations and a derived U eff, 261 cm-1, when the coupling between the d x 2-y 2 and dxy orbitals is taken into account, in very good agreement with ab initio calculations and superconducting quantum interference device results. Powder and single-crystal polarized neutron diffraction (PNPD, PND) have been used to quantify the magnetic anisotropy via the atomic susceptibility tensor, revealing that the easy axis of magnetization is pointing along the N-Co-N' bisectors of the N,N'-chelating ligands (3.4° offset), close to the molecular axis, in good agreement with complete active space self-consistent field/N-electron valence perturbation theory to second order ab initio calculations. This study provides benchmarking for two methods, PNPD and single-crystal PND, on the same 3d SIM, and key benchmarking for current theoretical methods to determine local magnetic anisotropy parameters.

The role of Co2+ cation addition in enhancing the AC heat induction power of (CoxMn1–x)Fe2O4 superparamagnetic nanoparticles

The physical role of magnetically semi-hard Co2+ cation addition in enhancing the AC heat induction temperature (T AC) or specific loss power (SLP) of solid (Co x Mn1−x )Fe2O4 superparamagnetic iron oxide nanoparticles (SPIONPs) was systematically investigated at the biologically safe and physiologically tolerable range of H AC (H AC,safe = 1.12 × 109 A m−1 s−1, f appl = 100 kHz, H appl = 140 Oe (11.2 A m−1)) to demonstrate which physical parameter would be the most critical and dominant in enhancing the T AC (SLP) of SPIONPs. According to the experimentally and theoretically analyzed results, it was clearly demonstrated that the enhancement of magnetic anisotropy (K u )-dependent AC magnetic softness including the Néel relaxation time constant τ N (≈τ eff , effective relaxation time constant), and its dependent out-of-phase magnetic susceptibility primarily caused by the Co2+ cation addition is the most dominant parameter to enhance the T AC (SLP). This clarified result strongly suggests that the development of new design and synthesis methods enabling to significantly enhance the K u by improving the crystalline anisotropy, shape anisotropy, stress (magnetoelastic) anisotropy, thermally-induced anisotropy, and exchange anisotropy is the most critical to enhance the T AC (SLP) of SPIONPs at the H AC,safe (particularly at the lower f appl < 120 kHz) for clinically safe magnetic nanoparticle hyperthermia.

Metal-insulator transition temperature in EuO1−x films as a function of exposure time in air

Oxygen-deficient Europium monoxide EuO1−x shows a metal-to-insulator transition near the Curie temperature (TC). A systematic transport study of EuO1−x thin films as a function of exposure time in air reveals a gradually decreased TC from 140 K to 70 K as the concentration of the oxygen vacancies decreases, which is accompanied by a drastic increase in the resistance. We also find an unusual enhancement of magnetic anisotropy in the transport measurements, which results from the strong spin-orbit coupling at the interface between the film and substrate and possible presence of spin-textures like skyrmions in EuO1−x.

Improvement of magnetostriction performance by doping Mg in spinel MnV2O4

By a combination of magnetization M(T), M(H) and strain ΔL/L700K, ΔL/L0Oe, the positive magnetostrictions up to ∼5000 ppm originating from the rearrangement of tetragonal domains were observed in spinel Mn0.85Mg0.15V2O4, which exhibits two successive magnetic transitions at TC ∼ 42 K and T* ∼ 28 K. An anomalous magnetic hysteresis loop under a high field occurs below T*, caused by the rearrangement of tetragonal domains. We found that the Mg-doping at the Mn site can effectively promote the positive magnetostriction in Mn1-xMgxV2O4 systems. Moreover, the remnant strain can be significantly lowered by Mg-doping due to the enhancement of magnetic anisotropy. These results provide a possible approach for further optimizing the performance of magnetic shape-memory materials.

Role of magnetic anisotropy on the heating mechanism of Co-doped Fe3O4 nanoparticles

The heating characteristics of CoxFe3-xO4 (x = 0, 0.1, and 0.3) nanoparticles of average particle size 10–12 nm were investigated. The electron spin resonance analysis revealed an enhancement in magnetic anisotropy from 16 to 21 kJm−3 with low Co doping of x = 0.1. Magnetic measurements performed at 15 K showed a coercivity of 290 kAm−1 for the x = 0.1 composition, that decreased to 37 kAm−1 on surface modification. The effective specific absorption rate (ESAR) obtained using infrared thermography demonstrated a decreasing trend from 3.16 to 2.84 nHm2kg−1 due to the increase in magnetic anisotropy associated with Co substitution. An increase in ESAR up to 4.42 nHm2kg−1 was estimated with surface modification of Co-doped Fe3O4. The theoretically estimated ESAR considering polydispersity and experimental results presented decreasing behavior with magnetic anisotropy as per the linear response theory.

Giant enhancement of perpendicular magnetic anisotropy and induced quantum anomalous Hall effect in graphene/ NiI2 heterostructures via tuning the van der Waals interlayer distance

Using first-principles calculations, we reveal that the perpendicular magnetic anisotropy of ${\mathrm{NiI}}_{2}$ monolayer can be effectively enhanced via decreasing the interlayer distance of graphene/${\mathrm{NiI}}_{2}$ (Gr/${\mathrm{NiI}}_{2}$) van der Waals (vdW) heterostructures. Furthermore, by analyzing the atomic-resolved magnetocrystalline anisotropy energy (MAE), orbital hybridization-resolved MAE and the density of states we elucidate that this magnetic anisotropy enhancement mainly originated from the electronic states change of $5p$ orbitals of interfacial I atoms. At the same time, we find that the ${\mathrm{NiI}}_{2}$ substrate induces strong magnetic proximity effects on graphene and the quantum anomalous Hall effect (QAHE) can be acquired by decreasing the interlayer spacing. Our work demonstrates the control of magnetic anisotropy of two-dimensional ferromagnetic materials via tuning vdW interlayer distance, and provides a van der Waals system to realize the QAHE.

Investigation of NiO reduction dynamics and properties of NiO-Ti powders

Abstract A detailed study of the mechanochemical (MC) processing of NiO-Ti [NiO-Ti (x at.%) with x = 20, 35] powders was carried out using a high-energy ball milling technique to investigate the formation of a NiO-based nanocomposite as a function of the milling time. During milling, the reduction of NiO to Ni follows a gradual process with a reduction of 10% and a self-sustaining process with a maximum reduction of 94% for x = 20 and 35 powders, respectively. The types of NiO reduction and the formation of ferromagnetic (FM) Ni from NiO could be accounted for by the change in magnetization to maximum values of 2 emu/g and 24 emu/g for the gradual and self-sustaining reactions, respectively. The relative fractions of Ni and NiO phases play an important role in (i) the formation of FM nanocomposite, (ii) the enhancement of magnetic anisotropy caused by the coexistence of mixed magnetic phases, (iii) temperature-induced structural phase changes and (iv) the gradual decrease in the induced FM phase with the increase in milling time. The process of time-dependent MC reduction and the resulting structural, vibrational and magnetic behavior of the in situ FM nanocomposite were studied in detail. This process may reveal potential applications in metallurgy and ore reduction processes.

Fe-Co-N薄膜へのAl添加による磁気異方性の増大

Fe-Co-N薄膜へのAl添加による磁気異方性の増大

Sol–gel combustion synthesis and antiferromagnetic properties of orthorhombic perovskite-type MFeO3:R3+ (M=La, Gd; R=Eu, Er, Ho) nanocrystalline powders

The MFeO3: R3+ (M ​= ​La, Gd; R ​= ​Eu, Er, Ho) nanocrystalline powders were successfully synthesized by the sol–gel combustion method using glycine-based gel at a low ignition temperature. The as-burnt products present honeycomb-like structure with many irregular continuous pores due to the releasing of a large amount of gas during the combustion reaction process. The lattice parameters and cell volumes of MFeO3:R3+ (M ​= ​La, Gd; R ​= ​Eu, Er, Ho) nanocrystalline powders are compared in detail. The magnetic properties of all the samples were studied systematically. The results show that the doping of rare-earth ions enhanced greatly the coercivity of GdFeO3 and LaFeO3 as a result of the enhancement of magnetic anisotropy. The influence of doped rare-earth ions on the magnetic properties was summarized. The distinction of magnetism of MFeO3:R3+ (M ​= ​La, Gd; R ​= ​Eu, Er, Ho) were explained in detail by the intrinsic magnetism of doped rare-earth ions. This work is significant for the application of rare-earth elements in other magnetic materials.

Gamma-irradiation induced modifications in structural and magnetic properties of nanocrystalline Mn0.5Zn0.5 SmxFe2-xO4 ceramics

The changes in structure, infrared absorption and magnetic property of nanocrystalline Mn0.5Zn0.5SmxFe2-xO4 (x = 0.01, 0.03 and 0.05) ceramics were studied after different doses (0, 15 and 25 kGy) of γ-irradiation. The samples were prepared by solution combustion route. We observed that up to the highest studied dose (25 kGy) of γ-irradiation all the samples retain the cubic spinel (Fd-3m) structure as of the pristine samples, however, the lattice parameter decreases. Furthermore, we observed the metastability of Sm (and Mn) atoms at the octahedral sites. By Sm3+ doping the saturation magnetization of the pristine samples decreases, but the magnetic coercivity increases drastically, indicating enhancement of magnetic anisotropy. After γ-irradiation the magnetic anisotropy vanishes completely and the sample behaves super-paramagnetically with a small variation in saturation magnetization. Our results are important to understand the behavior and stability of the magnetic hardness created by Sm3+ doping in soft magnetic Mn–Zn ferrite ceramics.

Tuning magnetic coercivity with external pressure in iron-rhenium based ferrimagnetic double perovskites

We studied the effect of physical pressure on the electronic and magnetic properties of ferrimagnetic double perovskites ${A}_{2}{\mathrm{FeReO}}_{6}$ ($A=\mathrm{Ca}$, Ba) using Re ${L}_{2,3}$ edge x-ray absorption spectroscopy and powder diffraction measurements. Volume compression is shown to dramatically increase the magnetic coercivity (${H}_{c}$) in polycrystalline samples of both compounds with $\mathrm{\ensuremath{\Delta}}{H}_{c}/\mathrm{\ensuremath{\Delta}}V\ensuremath{\sim}150$--200 $\mathrm{Oe}/{\AA{}}^{3}$. A nearly eight-fold increase in ${H}_{c}$, from 0.2 to 1.55 T, is obtained in ${\mathrm{Ba}}_{2}{\mathrm{FeReO}}_{6}$ at $P=29$ GPa. While no signs of structural phase transitions are seen in either sample to $\ensuremath{\sim}30$ GPa, the structural data points to a pressure-driven increase in tetragonal distortion of ${\mathrm{ReO}}_{6}$ octahedra. A sizable but pressure-independent Re orbital-to-spin magnetic moment ratio is observed, pointing to the critical role of spin-orbit interactions at Re sites. We present a ${j}_{\mathrm{eff}}$ description of the electronic structure that combines effects of crystal field and spin-orbit coupling on the Re $5{d}^{2}$ orbitals and use this description to provide insight into the pressure-induced enhancement of magnetic anisotropy.

Effect of oxygen potential on Co solubility limit in La–Co co-substituted magnetoplumbite-type strontium ferrite

La–Co co-substituted magnetoplumbite-type (M-type) strontium ferrite is typically used as a base material for high-performance hard ferrite magnets. Generally, the unquenched orbital moment of Co2+, substituted for Fe3+, is thought to enhance magnetic anisotropy and then coercivity. La3+ is substituted for Sr2+ to compensate for the charge unbalance associated with Co2+ substitution. Even if the synthesis starts with equal amounts of Co and La, the Co contents of the resulting samples are generally lower than the La contents because of the partial reduction of Fe3+ to Fe2+. We studied how the oxygen potential suppresses the formation of Fe2+ and expands the Co solubility range in this system. Polycrystalline samples, synthesized under oxygen partial pressures of 0.2, 1.0, and 387 atm, were characterized by powder X-ray diffraction, wavelength-dispersive X-ray analysis, and magnetization measurements. We reveal that the application of higher oxygen pressure dramatically expands the Co solubility range, resulting in the enhancement in magnetic anisotropy. We successfully synthesized Sr-free LaFe11CoO19 with high magnetic anisotropy using the hot isostatic pressure (HIP) technique.

Determination of specific ion positions of Cr3+ and O2− in Cr2O3 thin films and their relationship to exchange anisotropy at Co/Cr2O3 interfaces

The structures of antiferromagnetic Cr2O3(0001) thin films with perpendicular exchange bias were investigated using reflection high-energy electron diffraction, X-ray reflectivity, and synchrotron X-ray diffraction. We mainly investigated the specific ion positions of Cr3+ and O2− in the corundum structure and discussed their relationship to the magnetic anisotropy of Cr2O3. The Cr2O3(0001) thin film grown on a Pt(111) buffer layer exhibited a perpendicular exchange anisotropy density of 0.42 mJ/m2, in which the Cr3+ position is the primary factor in the enhancement of magnetic anisotropy due to dipolar-interaction. In contrast, the single-crystalline Cr2O3(0001) film grown on a α-Al2O3(0001) substrate featured a low exchange magnetic anisotropy of 0.098 mJ/m2. In this film, the Cr3+ position parameter is an insignificant factor, leading to low magnetic anisotropy. The O2− ion position also differs between the two types of films, which can affect both the magnetic anisotropy energy originating from fine structures and the magneto-electric properties of Cr2O3.

Site dependent enhancement of magnetic anisotropy in 4d and 5d impurity doped α″-Fe16N2: A first principles study

Using the first principles method, we studied the electronic structure and magnetocrystalline anisotropy of site dependent 4d, 5d element doping in α″-Fe16N2. We found that different Fe sites contributed differently for magnetocrystalline anisotropy. For instance, on d-site doping, we obtained perpendicular magnetocrystalline anisotropy while the h-site doping resulted in an in-plane magnetocrystalline anisotropy in all the studied systems. The impurity doping induces local lattice distortions near the impurity site. However, the volume of the cell and total magnetic moment of the doped systems were not much affected. This local lattice distortion together with the spin-orbit coupling effect associated with heavy 4d, 5d element mainly contributed to enhancing the magnetocrystalline anisotropy. The enhancement of the magnetocrystalline anisotropy results in almost 15 to 67% enhancement of the coercivity for 4d element doping while we found 80 to 137% enhancement for 5d element doping. The maximum energy products were also enhanced compared to the pure α″-Fe16N2. The maximum enhancement was observed in Rh and Pt doped systems where the energy products were 119–120 MGOe. These results may suggest that substitutional doped α″-Fe16N2 system can be used as potential rare earth free permanent magnet.

Large magnetic anisotropy and strain induced enhancement of magnetic anisotropy in monolayer TaTe2.

Monolayer TaTe2 holds great potential for the realization of large magnetocrystalline anisotropy due to strong spin-orbit coupling (SOC) interactions of Ta. Here, we systematically investigate the electronic structure, magnetism and magnetocrystalline anisotropy of monolayer TaTe2 under different strains by means of first-principles calculations. The results show that monolayer TaTe2 is a ferromagnetic metal and exhibits a large in-plane magnetic anisotropy energy (MAE) of -11.38 meV per TaTe2. It is worth noting that the magnetic moment, magnetic coupling and magnetic anisotropy of monolayer TaTe2 are significantly enhanced by strain. In particular, when tensile strain increases from 0% to 8%, the MAE of monolayer TaTe2 greatly increases from -11.38 to -15.14 meV per TaTe2. By analyzing the density of states and the contribution to magnetocrystalline anisotropy (MCA) from the SOC interaction between two d orbitals of Ta atoms based on second-order perturbation theory, it is concluded that a large MAE of monolayer TaTe2 is mainly contributed by the SOC interaction between opposite spin dxy and dx2-y2 orbitals of Ta atoms and the significant increase of the negative contribution to MCA from the SOC interaction between opposite spin dxy and dx2-y2 orbitals under strain is the reason why the MAE of monolayer TaTe2 is significantly enhanced by strain. Our results indicate that monolayer TaTe2 is a promising candidate suitable for applications in magnetic storage devices.

Effect of Boron Addition on Magnetic-Domain Structure of Rapidly Quenched Zr2Co11−Based Nanomaterials

The boron-content dependence of magnetic domain structures and magnetic properties of nanocrystalline Zr16Co82.5−x Mo1.5B x (x = 0, 1, 2, 3, 4) melt-spun ribbons have been investigated. Compared to x = 0, the smaller average domain size with a relatively short magnetic correlation length of 120 nm and largest root-mean-square phase shift value of 0.94° are observed for x = 1. The best magnetic properties of coercivity H c = 5.4 kOe, maximum energy product (BH) max = 4.1 MGOe, and saturation polarization J s = 7.8 kG, were obtained for the ribbon with x = 1. The optimal B addition enhances the content of hard magnetic phase, promotes magnetic domain structure refinement, and increases the surface roughness, results in the enhancement of magnetic anisotropy, and thus leads to a significant increase in coercivity and energy product in this sample.

Large magnetic anisotropy enhancement in size controlled Ni nanowires electrodeposited into nanoporous alumina templates

A large enhancement of the magnetic anisotropy of Ni nanowires (NWs) embedded in anodic aluminium oxide porous membranes is obtained as a result of an induced magnetoelastic (ME) anisotropy contribution. This unusual large anisotropy enhancement depends on the diameter of the NWs and exceeds the magnetostatic (MS) contribution. As a consequence, it leads to effective magnetic anisotropy energies as large as erg cm−3, which are of the same order of magnitude and comparable to the MS energies of harder magnetic materials like Co NWs. Specifically, from ferromagnetic resonance experiments, the magnetic anisotropy of the NWs has been observed to increase as its diameter is decreased, leading to values that are about four times larger than the corresponding value when only the MS anisotropy is present. Our results are consistent with the recently proposed growth mechanism of Ni NWs that proceeds via a poly-crystalline stage at the bottom followed by a single-crystalline stage with texture [110] parallel to the axis of the NWs. A strong correlation between reducing the diameter of the NWs with the decrease of the length of the poly-crystalline segment and the enhancement of the effective magnetic anisotropy has been shown. Magnetization curves obtained from alternating gradient magnetometry experiments show that the average ME anisotropy results from the competition between the magnetic anisotropies of both crystalline segments of the NWs. Understanding the influence of size and confinement effects on the magnetic properties of nanocomposites is of prime interest for the development of novel and agile devices.