Values Of Magnetic Anisotropy Research Articles

Temperature dependent interfacial-coupling and magnetization reversal of La2/3Sr1/3MnO3 film with inverted hysteresis features

Temperature-dependent magnetic anisotropy and interfacial coupling of La2/3Sr1/3MnO3 (LSMO) epitaxial films with inverted hysteresis (IHLs) features are investigated using a broadband ferromagnetic resonance (FMR) spectrometer. Through the dispersion relation obtained along [100], [110] and [010] axes, a simplified method is proposed to investigation in-plane magnetic anisotropy by broadband FMR in a cryostat. According to this method, the perpendicular uniaxial anisotropy, magneto-crystalline anisotropy, and interfacial coupling between the LSMO film and hard-magnetic interface layer are investigated as a whole. The measured value of interfacial coupling is −17.6 Oe at 300 K, close to the bias field found in minor loop, i.e., −18.4 Oe. The interfacial coupling is enhanced with the dropping of temperatures, and the value of interfacial coupling changed to −112 Oe at 10 K. A Stoner-Wohlfarth-like model is employed to calculate the hysteresis loops of the films based on the measured values of in-plane magnetic anisotropy and interfacial-coupling. The calculation reveals the mechanism of magnetization reversal and the origin of IHLs found in LSMO films.

Three coordinated first row-transition metal complexes, [M{N(SiMe3)2}3]−1/0: Structure, bonding, and magnetic properties

Structure, bonding, and magnetic properties of [M{N(SiMe3)2}3]−1/0 (M = first row-transition metal, Sc-Cu in + 2/+3 oxidation state) complexes are studied. The atoms in molecules (AIM) analysis shows that non-covalent interactions between the methyl hydrogens are prevalent. Energy decomposition analysis coupled with natural orbital for chemical valence (EDA-NOCV) analysis shows that the ligand is bonded to the metal ions through σ and π bonding. In addition, the reasonable contribution from the dispersion interaction supports van der Waals' type of interaction. The highest value of magnetic anisotropy (D) is calculated in the NiII complex with a value of −382.945 (−234.145) cm−1 at the CASSCF (NEVPT2) level of theory. It is significantly higher than the previously reported values of −14.644 (−15.631) and −63.691 (−64.000) cm−1 in similar CrII and MnIII complexes, respectively. Ab Initio Ligand Field Theory (AILFT) is utilized to calculate the splitting of the d-orbitals in all the metal complexes. In the NiII complexes, the blocking barrier (Ueff) is found to be 127 cm−1. Thus, it has a high potential to be utilized as a single ion magnet (SIM).

Investigation of Nearest Neighbor Interactions in Nickel Substituted Cobalt Using 59Co IFNMR

Co100-x Nix (x = 10, 20, 30, 40) alloys were synthesized via the chemical method by reducing nitrates of cobalt and nickel using hydrazine as a reducing agent. The proportion of solvents, ethanol, and water was maintained constant for all the samples in the series. The structure and morphology of the samples were examined based on X-Ray diffraction (XRD) data and Scanning Electron Microscope (SEM) images. From XRD it was evident that the system had a mixture of hexagonal close packed (hcp) and face centered cubic (fcc) phases. The amount of hcp phase in the composition gradually reduced as the concentration of nickel increased. The effect of substitution of nickel on cobalt was studied using a home built 59Co internal field nuclear magnetic resonance (IFNMR) spectrometer. Further, the saturation magnetization and hence magnetic field anisotropy values, obtained from M vs H loops, are found to vary with nickel concentration. The NMR results show a broadening of the NMR signals in comparison with the pure phase of cobalt. The NMR spectra and the number of peaks were assigned to possible cobalt-nickel neighbors, and the percentage of such combinations is interpreted in terms of the frequency and intensity of the peaks. This percentage of different nickel-cobalt combinations was compared with the random distribution obtained using the binomial distribution function. This comparison shows a clear trend compared to that analysed by the IFNMR experiment.

Enhancement in the dielectric and magnetic properties of Ni2+-Cu2+ co-doped BaFe11Cu1-xNixO19 hexaferrites (0.0 ≤ x ≤ 1.0).

Herein, Ni2+-Cu2+ co-doped barium hexaferrites (BaFe11Cu1-xNixO19, 0.0 ≤ x≤ 1.0 with an interval of 0.25) were successfully synthesized using a co-precipitation method. The formation of a magnetoplumbite structure with the P63/mmc space group was confirmed by Rietveld refinement of the obtained X-ray diffraction patterns. Microstructural investigations revealed grains in the shape of hexagonal plates, while co-doping resulted in a variation in the grain sizes of the prepared samples. X-ray photoelectron spectroscopy was performed to determine the valence state of iron in the prepared hexaferrites. Impedance spectroscopy analysis revealed that dielectric permittivity initially decreased with an increase in the co-dopant content up to x = 0.5 and then increased by two orders of magnitude for x = 1.0. Alternatively, resistive properties showed microstructural resistance values in the range 105-108 Ω, with the highest value obtained for the sample with x = 0.5. Furthermore, magnetic measurements indicated that all the prepared samples exhibited ferrimagnetic behaviour. Saturation magnetization and magnetic anisotropy values were found to be the highest for the sample with x = 1.0, which also had the lowest coercivity among the prepared samples. Herein, the observed variations in the obtained results can be explained by the variations in grain sizes and the Fe2+/Fe3+ ratio associated with the preferential occupation of co-dopants at octahedral sites. Based on our findings, the BaFe11Ni1O19 (x = 1.0) composition appears to be the most promising choice as a microwave absorption material among the prepared samples owing to the coexistence of high dielectric permittivity (>103 at 107 Hz) and saturation magnetization (73 emu g-1).

Optimization of growth conditions to obtain highly anisotropic FeCo nanowires prepared through magnetic-field-assisted chemical route

In this study, we synthesized one-dimensional α-FeCo nanowires using the magnetic-field-assisted hydrazine reduction method. The amount of hydrazine, NaOH, synthesis temperature and strength of the magnetic field were optimized to obtain high aspect ratio nanowires with good quality. Two samples, obtained at 90 °C (S12) and 60 °C (S34) with improved morphologies and aspect ratios, while keeping the other optimized conditions (Hydrazine - 1 mL; NaOH - 1.5 g and strength of the magnetic field - 4000 Gauss (G)) same, were characterized using various techniques viz. X-ray diffraction (XRD), High-resolution transmission electron microscopy (HR-TEM), selected area electron diffraction (SAED), X-ray photoemission spectroscopy (XPS) and dc-magnetization to investigate structural, electronic structural and magnetic properties. Both the samples revealed single-phase α-FeCo formation with body centered cubic (BCC) geometry with space group: Im-3m indicating decrease in the lattice parameter and crystallite dimensions at 60 °C (S34). The influence of synthesis temperature was notably observed on the magnetic properties as well. The saturation magnetization was found to be enhanced from 233 emu/g for S12 to 247 emu/g for S34 along with the enhancement in coercivity. The effective magnetic anisotropy also enhanced to be 2.3× 106 erg/cm3 in S34. In brief, the improvement in aspect ratio and morphology of the wires resulted in the enhancement of saturation magnetization and effective magnetic anisotropy. The enhanced value of magnetocrystalline anisotropy and shape magnetic anisotropy is attributable to the external magnetic field applied during growth and curling of spins due to the reduced diameter of the wires.

Evaluation of structural, optical, and magnetic properties of Gd doped MnFe2O4 nanoparticles

In this study, the MnFe2O4 doped Gd (MnGdxFe2-xO4 with x = 0, 0.125, 0.25, and 0.5) magnetic nanoparticles were successfully synthesized and revealed the significant effect of Gd content on structural, optical, and magnetic properties. The replacement of Fe3+ ions by ion Gd3+ ions changed the crystallite size from 8.2 nm (x = 0) to 13.5 nm (x = 0.5). The band gap of Gd-doped MnFe2O4 increased with an increase of the x value. The magnetic curves showed that saturation magnetization (MS) and magnetic anisotropy (K) decreased simultaneously with the concentration of Gd3+ ions. The MS value reduced from 54.0 emu/g (MnFe2O4) to 35.4 emu/g (MnGd0.5Fe1.5O4). The K value dropped from 50.4 kJ/m3 (MnGd0.125Fe1.875O4) to 12.3 kJ/m3 (MnGd0.5Fe1.5O4). The substantial reliance of magnetic anisotropy on the doping concentration, namely this large change in K with a little change in size (8.2 nm–13.5 nm), demonstrated that doping is a suitable method for modifying the values of magnetic anisotropy of materials.

Rapid and Accurate Prediction of the Axial Magnetic Anisotropy in Cobalt(II) Complexes Using a Machine-Learning Approach.

Estimating the magnetic anisotropy for single-ion magnets is complex due to its multireference nature. This study demonstrates that deep neural networks (DNNs) can provide accurate axial magnetic anisotropy (D) values, closely matching the complete-active-space self-consistent-field (CASSCF) quality using density functional theory (DFT) data. We curated an 86-parameter database (UFF1) with electronic data from over 33000 cobalt(II) compounds. The DNN achieved an R2 of 0.906 and a mean absolute error of 18.1 cm-1 in comparison to reference CASSCF D values. Remarkably, it is 11 times more accurate than DFT methods and 7700 times faster. This approach hints at DNNs predicting the anisotropy in larger molecules, even when trained on smaller ligands.

Strain and voltage control of the magnetic anisotropy in Co2MnSi thin film

The strain effect on the magnetic anisotropy (MA) in free-standing Co2MnSi(001) thin film and the voltage control MA in Au-capped MgO/Co2MnSi thin film are investigated within the framework of density functional theory. We find that the MA of free-standing film with MnSi-termination is sensitive upon strain, while the magnetic easy axis changes from in-plane to out-of-plane under the applied in-plane 1% extension strain. The MA of Au-capped Co2MnSi/MgO shows a ∧-shaped electric-field dependence and a large voltage-controlled MA value (VCMA) of 225 fJ (Vm)−1. The VCMA is caused by the change of the spin-flip term, which is related to the energy shift of the Co dz 2 minority-spin band near the Fermi level. Based on this study, it is expected that Co2MnSi can potentially be used in magnetoelectric spintronic devices.

Nonrelaxational FMR peak broadening in spatially inhomogeneous films

The modification of magnetic properties in spatially inhomogeneous epitaxial films of magnetic shape memory alloys in martensitic state with the temperature variation has been studied. The proposed theoretical model is based on Landau theory of martensitic transformation and statistical model of martensitic state. It was shown that that spatial inhomogeneity of the material leads to the dispersion of local martensitic transformation temperatures resulting in the variation of local magnetic anisotropy values. This model allows describing the dramatic ferromagnetic resonance line broadening observed in the experiments in epitaxial films of magnetic shape memory alloys at low temperatures.

Analysing the super exchange interaction of Fe3+-O2--Cr3+ on multiferroic structured BiFeO3/LaCrO3 nanocomposite

Herein, we report a successful attempt to synthesise a material based on the theory proposed by Goodenough and Kanamori et al. This report details the super-exchange magnetic interaction of Fe3+-O2--Cr3+ taking place between BiFeO3/LaCrO3 nanocomposite. The tilt in FeO6's octahedral sites cancels out the tilt in the CrO6 site, making it an ideal perovskite explained through nearest neighbouring interaction (NN), with the next nearest neighbour interaction (NNN) pointing the way to possible ferromagnetic exchange in Fe3+-O2--Cr3+. The significant enhancement of retentivity (residual magnetism) in BiFeO3/LaCrO3 nanocomposite is three times that of the pristine material. The material's high coercive nature (351.35 Oe) makes it suitable for hard magnet applications. The correlation between magnetic anisotropy value and the first-order derivative (dM/dH) of M − H data concludes the successful construction of Fe–O–Cr interaction for magnetic applications.

Effect of annealing on the magnetic microstructure of high-pressure torsion iron: the relevance of higher-order contributions to the magnetic small-angle neutron scattering cross section.

The development of higher-order micromagnetic small-angle neutron scattering theory in nanocrystalline materials is still in its infancy. One key challenge remaining in this field is understanding the role played by the microstructure on the magnitude and sign of the higher-order scattering contribution recently observed in nanocrystalline materials prepared by high-pressure torsion. By combining structural and magnetic characterization techniques, namely X-ray diffraction, electron backscattered diffraction and magnetometry with magnetic small-angle neutron scattering, this work discusses the relevance of higher-order terms in the magnetic small-angle neutron scattering cross section of pure iron prepared by high-pressure torsion associated with a post-annealing process. The structural analysis confirms: (i) the preparation of ultra-fine-grained pure iron with a crystallite size below 100 nm and (ii) rapid grain growth with increasing annealing temperature. The analysis of neutron data based on the micromagnetic small-angle neutron scattering theory extended to textured ferromagnets yields uniaxial magnetic anisotropy values that are larger than the magnetocrystalline value reported for bulk iron, supporting the existence of induced magnetoelastic anisotropy in the mechanically deformed samples. Furthermore, the neutron data analysis revealed unambiguously the presence of non-negligible higher-order scattering contributions in high-pressure torsion iron. Though the sign of the higher-order contribution might be related to the amplitude of the anisotropy inhomogeneities, its magnitude appears to be clearly correlated to the changes in the microstructure (density and/or shape of the defects) induced by combining high-pressure torsion and a post-annealing treatment.

Origin of Magnetic Anisotropy in Nickelocene Molecular Magnet and Resilience of Its Magnetic Behavior

The robustness of nickelocene’s (NiCp2, Cp = cyclopentadienyl) magnetic anisotropy and addressability of its spin states make this molecular magnet attractive as a spin sensor. However, microscopic understanding of its magnetic anisotropy is still lacking, especially when NiCp2 is deposited on a surface to make quantum sensing devices. Quantum chemical calculations of such molecule/solid-state systems are limited to density functional theory (DFT) or DFT+U (Hubbard correction to DFT). We investigate the magnetic behavior of NiCp2 using the spin-flip variant of the equation-of-motion coupled-cluster (EOM-SF-CC) method and use the EOM-SF-CC results to benchmark SF-TD-DFT. Our first-principle calculations agree well with experimentally derived magnetic anisotropy and susceptibility values. The calculations show that magnetic anisotropy in NiCp2 originates from a large spin–orbit coupling (SOC) between the triplet ground state and the third singlet state, whereas the coupling with lower singlet excited states is negligible. We also considered a set of six ring-substituted NiCp2 derivatives and a model system of the NiCp2/MgO(001) adsorption complex, for which we used SF-TD-DFT method. To gain insight into the electronic structure of these systems, we analyze spinless transition density matrices and their natural transition orbitals (NTOs). The NTO analysis of SOCs explains how spin states and magnetic properties are retained upon modification of the NiCp2 coordination environment and upon its adsorption on a surface. Such resilience of the NiCp2 magnetic behavior supports using NiCp2 as a spin-probe molecule by functionalization of the tip of a scanning tunneling microscope.

Synthesis, crystal structure and NMR-study new mononuclear paramagnetic Er (III) complex based on imine derivatives of thiacalix[4]arene

The synthesis, crystal structure and NMR-study of new paramagnetic Er (III) complex based on imine derivatives of thiacalix[4]arene was carried out. Temperature dependences of the 1H NMR spectra of complex Er(III) and calix[4]arene with N-contained substituents (I) have been analyzed using the line shape analysis, taking into account the temperature variation of paramagnetic chemical shifts, within the frame of the dynamic NMR method. Two kinds of molecular dynamics in I are reported for the CDCl3 solution. The first one conformational dynamics is conditioned by the pinched cone A ↔ pinched cone B interconversion with activation free energy ΔG≠(298 K) = 40 ± 3 kJ/mol (observed at low temperature). The second one dynamics is connected with rearrangements in coordination environment (with ΔG≠(298 K) = 58 ± 3 kJ/mol). Due to substantial temperature dependence of paramagnetic shifts, the complex I can be considered as NMR thermosensor reagent for local temperature monitoring. Owing to the large magnetic moments typical for many Ln-ions and especially high value of magnetic anisotropy for Er cation (III) adopting capped trigonal prismatic geometry of coordination sphere one may expect that 1-Er can potentially exhibit SMM behavior.

Comprehensive Law‐of‐Approach‐to‐Saturation for the Determination of Magnetic Anisotropy in Soft Magnetic Materials

Magnetocrystalline anisotropy is a crucial parameter that determines the suitability of magnetic material in a wide range of emerging applications. The law‐of‐approach‐to‐saturation (LAS), utilized to obtain the magnetocrystalline anisotropy from hysteresis loops, is not satisfactory for materials with cubic anisotropy as they are two orders higher than the bulk value. Herein, a modified formulation to LAS is presented, where the reduction in effective magnetic anisotropy (K) values due to Fe oxide phases in Fe particles over wide size ranges is accounted. The value ofKdecreases from 4.2 × 104 J m−3for the Fe particles of average size 210 nm to 1.2 × 104 J m−3for the 20 nm particles due to the increase in the iron oxide fraction with size reduction. The effective magnetic anisotropy obtained from the modified LAS has been validated from the ferromagnetic resonance studies for particles of the smallest size.

Manipulation of Antiskyrmion Phase in Mn2+xNi1−xGa Tetragonal Heusler System

The inhomogeneous magnetization distribution in antiskyrmions helps in nullifying the unwanted skyrmion Hall effect generally found in the current driven motion of skyrmions. At present, the observation of room-temperature antiskyrmion phase is limited to only a very few materials. Here, we present the evidence of a tunable antiskyrmion phase in the ${D}_{2d}$-symmetry-based tetragonal Heusler system ${\mathrm{Mn}}_{2+x}{\mathrm{Ni}}_{1\ensuremath{-}x}\mathrm{Ga}$. With the help of dc magnetization, ac susceptibility, and topological Hall effect measurements, we demonstrate that the potential antiskyrmion phase can be tuned over a wide compositional range with magnetic ordering temperature of above 600 K. In addition, we find the existence of multiple topological phase transitions for a certain Mn/Ni ratio where the magnetic anisotropy attains its maxima. Our micromagnetic simulations suggest that the transition from antiskyrmionium and antiskyrmion pockets to the conventional antiskyrmion phase at the optimal value of magnetic anisotropy might be responsible for the observed multiple topological transitions in the present materials. The expected small size of antiskyrmions in the present low magnetic-moment-based ferrimagnetic system gives a great advantage over other skyrmion and antiskyrmion hosting materials for their potential application in racetrack-based memory devices.

Compositional Dependence of Magnetocrystalline Anisotropy in Fe-, Co-, and Cu-Alloyed Ni-Mn-Ga

The key for the existence of magnetic induced reorientation is strong magnetocrystalline anisotropy, i.e., the coupling between ferroelastic and ferromagnetic ordering. To increase the transformation temperatures and thus functionality, various elemental alloying in Ni-Mn-Ga is tried. We analyzed more than twenty polycrystalline alloys alloyed by small amount (up to 5atom%) of transitional metals Co, Fe, Ni, and Cu for the value of magnetic anisotropy in search of general trends with alloying. In agreement with previous reports, we found that maximum anisotropy occurs at stoichiometric Ni2MnGa and any alloying decreases its value. The strongest decrease of the anisotropy is observed in the case where the alloyed elements substitute Ga.

Adiabatic Switching Among Quantum Dot Eigenstates: Role of Anharmonicity and Gaussian White Noise

Current study inquires the time‐dependent quantum adiabatic switching (TDQAS) among the quantum dot (QD) eigenstates under the aegis of Gaussian white noise (GWN) with special emphasis on anharmonicity that may be present in the QD potential. The initial and the final eigenstates are distinguished by different values of magnetic field strength, confinement potential, anisotropy, and anharmonicity. The QAS has been conducted using four different switching functions (SFs), e.g., square, exponential, sinusoidal, and logarithmic. The time development of switching has been monitored with the help of overlap function and quantum information entropy (QIE). The SFs appear to recover the eigenstates of QD corresponding to the final Hamiltonian. The switching paths comprise features such as enhancement, depletion, maximization, minimization, and crossover of the overlap function and entropy. These characteristics of switching paths depend on presence/absence of noise, its pathway of application (additive/multiplicative), and symmetry (odd/even) of the anharmonic potential. The dependence on the type of SF used, however, has been found to be not much significant unless the exclusive role of noise strength on switching path is observed. The study merits importance in view of immense technological applications of QD‐based systems where the noise‐anharmonicity interplay may be exploited to a great extent.

Thickness induced magnetic anisotropic properties of Tb-Fe-Co thin films

The influence of Tb25Fe61Co14 thin film thicknesses varying from 2 to 300 nm on the structural and magnetic properties has been systematically investigated by using of X-ray diffraction, scanning electron microscopy, transmission electron microscopy, magnetization, and magneto-optic Kerr effect microscopy measurements. Thin film growth mechanism is pursued and controlled by ex-situ X-ray refractometry measurements. X-ray diffraction studies reveal that the Tb25Fe61Co14 films are amorphous regardless of thin films thicknesses. The magnetic properties are found to be strongly related to thickness and preferred orientation. With an increase in film thickness, the easy axis of magnetization is reversed from in-plane to out-of-plane direction. The change in the easy axes direction also affects the remanence, coercivity and magnetic anisotropy values. The cause for the magnetic anisotropy direction change from in-plane to out-of-plane can be related to the preferred orientation of the thin film which depends on the large out-of-plane coercivity and plays an important role in deciding the easy axes direction of the films. According to our results, up to the 100 nm in-plane direction is dominated over the whole system under major Fe-Fe interaction region, after that point, the magnetic anisotropy direction change to the out-of-plane under major Tb-Fe/Tb-Co interaction region and preferred orientation dependent perpendicular magnetic anisotropic properties become more dominated with 2.7 kOe high coercive field values.

Eddy Current Sensor System for Tilting Independent In-Process Measurement of Magnetic Anisotropy.

Modern production equipment is based on the results of quality control as well as process parameters. The magnetic anisotropy of materials is closely connected to internal mechanical stress by the Villari effect, and also to hardening effects due to plastic deformations, and could therefore provide an interesting basis for process control. Nevertheless, the analysis of anisotropic properties is extremely sensitive to sensor and workpiece misalignments, such as tilting. In this work, a novel eddy current sensor system is introduced, performing a non-contact measurement of the magnetic anisotropy of a workpiece and realizing a separation and correction of tilting effects. The measurement principle is demonstrated with the example of two samples with different magnetic anisotropy values induced by cold forming. Both samples are analyzed under different tilt angles between the sensor axis and the surface of the workpiece. In this work, digital signal processing is demonstrated on the acquired raw data in order to differentiate the effects of tilt and of anisotropy, with the use of preliminary results as an example of two prepared samples.

Enhancement of Hard Magnetic Properties in Fraktal-Like Nano and Mesoscopic Grains.

The paper refers to Monte Carlo magnetic simulations for fractal-like nano and mesoscopic grains. The analyzed objects differed in the size, surface development, magnetic anisotropy and the spin values attributed to the system nodes inside the fractal. Such an approach allowed us to determine their magnetization processes as well as optimization characteristics in the direction to enhancement of hard magnetic properties. As it was shown, the size effects depend on the chosen value of magnetic anisotropy. In the case of fractals with ultra-high coercivity, the decreasing of their size leads to deterioration of coercivity, especially for the high surface to volume ratio. Opposite effects were observed for soft magnetic fractals when the nanostructure caused an appearance of the coercive field, and the maximum of energy product was predictably significantly higher than for conventional rare earths’ free permanent magnets.