Uniaxial Magnetic Anisotropy Energy Research Articles

Enhancing the Thermal Stability of Skyrmion in Magnetic Nanowires for Nanoscale Data Storage

Magnetic skyrmion random switching and structural stability are critical limitations for storage data applications. Enhancing skyrmions’ magnetic properties could improve their thermal structural stability. Hence, micromagnetic calculation was carried out to explore the thermal nucleation and stability of skyrmions in magnetic nanodevices. Different magnetic properties such as uniaxial magnetic anisotropy energy (Ku), saturation magnetization (Ms) and Dzyaloshinskii—Moriya interaction (DMI) were used to assess the thermal stability of skyrmions in magnetic nanowires. For some values of Ms and Ku, the results verified that the skyrmion structure is stable at temperatures above 800 K, which is higher than room temperature. Additionally, manipulating the nanowire geometry was found to have a substantial effect on the thermal structural stability of the skyrmion in storage nanodevices. Increasing the nanowire dimensions, such as length or width, enhanced skyrmions’ structural stability against temperature fluctuations in nanodevices. Furthermore, the random nucleation of the skyrmions due to the device temperature was examined. It was shown that random skyrmion nucleation occurs at temperature values greater than 700 K. These findings make skyrmion devices suitable for storage applications.

Continuous strain-mediated perpendicular magnetic anisotropy in epitaxial (111) CoFe2O4 thin films grown on LiTaO3 substrates

Perpendicular magnetic anisotropy (PMA) in magnetic thin films has attracted much attention due to its potential applications in spintronics devices. Here, we report the continuous strain-mediated PMA in epitaxial (111) CoFe2O4 (CFO) thin films grown on (0001) LiTaO3 substrates. A large variation in lattice strain (∼0.9%) in a continuous way is realized in the CFO thin films by changing substrate temperature during deposition due to the difference in the thermal expansion coefficient between CFO and LiTaO3. As a result, the PMA of the (111) CFO thin films can be continuously mediated by the strain with uniaxial magnetic anisotropy energy in the range of 0.12-14.69×106 erg/cm3. Furthermore, the strain as well as the consequent PMA in the (111) CFO thin films can be maintained within the thickness of 25–205 nm, which is consistent with the scenario of the magnetoelastic effect. Our results reveal that the CFO/LiTaO3 system can be regarded as an ideal platform to realize robust PMA and its continuous strain tuning in the (111) CFO thin films by virtue of strain-induced magnetic anisotropy.

Effects of Buffer and Capping Layers on Thermal Stability of CoFeB/MgO Frames at Various Temperatures

The utilization of CoFeB thin films in spintronic devices has attracted significant attention due to their exceptional magnetic properties, which include high saturation magnetization and spin polarization. However, the effect of ambient temperature on the magnetic properties of CoFeB/MgO frames, particularly those with different buffer and capping layers, remains unexplored. Therefore, in this study, the magnetostatic and dynamic properties of CoFeB/MgO frames were investigated at various temperatures. Using vibrating sample magnetometry and ferromagnetic resonance spectroscopy, changes in key parameters such as saturation magnetization, the Gilbert damping constant, magnetic anisotropy field, in-plane uniaxial magnetic anisotropy energy, and thermal stability factor were investigated. Furthermore, the thermal stabilities of CoFeB/MgO frames with Ta buffer and capping layers were compared with those of CoFeB/MgO frames with W buffer and capping layers by examining the changes in the key parameters at various temperatures. These results reveal that the thermal stability of the latter surpassed that of the former. This study provides significant insights for the development of thermally robust spintronic devices capable of operating above room temperature.

First-principles study on the enhancement of structure stability and magnetocrystalline anisotropy energy of L10-ordered Mn1−xFexAlC compound for permanent magnet application

L10-MnAl exhibits excellent magnetic properties and could be used as a candidate to fill the gap between hard ferrite and rare-earth based permanent magnet (PM) applications. However, one of the major problems with L10-MnAl is that the structure is metastable and decomposes to other structural phases at higher temperature. Therefore, enhancing the structure stability of L10-MnAl is essential for PM applications. We studied the prospect of improving the structural stability and increasing the uniaxial magnetic anisotropy energy (Ku) of the L10-MnAl structure in this work. It is found that C-doping at the 1d interstitial site enhanced the structure stability of the compound. Moreover, Fe substitution on Mn sites shows a significant increase in the uniaxial magnetic anisotropy energy (Ku). Therefore, the electronic structure and magnetic properties of L10-ordered Mn1−xFexAlC (x = 0, 0.125, 0.250, 0.375, 0.50, 0.625, 0.75, and 0.87) alloys are investigated by using the first-principles calculations. The results show that x = 0.375 Fe content in the L10-MnAl alloy and 6% doping of C maintained the structural stability and provided a maximum value of Ku = 2.13 (MJ/m3), which is 25% higher than for the pristine L10-MnAl, making it suitable for permanent magnet applications.

3d transition metal substituted Fe3Se4: prediction of potential permanent magnet

It is crucial for modern condensed matter physics to be able to effectively manipulate magnetism, as well as for permanent applications in general. The pristine Fe3Se4 is known to meet all the criteria for a good permanent magnet (PM), but its energy product is quite low due to its low magnetization. Based on density functional theory calculations, we report on improved magnetic properties of promising transition metal (TM) substituted Fe3Se4 systems (TM0.5Fe2.5Se4 and TM1Fe2Se4, with TM = Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and Zn). The stability of the compounds is determined using phonon density of states and enthalpy of formation calculations. We predict an enhanced magnetization as well as uniaxial magnetic anisotropy energy (MAE) for TM substituted Fe3Se4, reaching a maximum value of = 1.416 MJ m−3 for V1Fe2Se4. We investigate the electronic structure of the compounds, and explore the source of the improved MAE. The enhanced MAE in V1Fe2Se4 is attributed to the in-plane 3d orbitals near the Fermi level, E F, which alters the overall electronic bands. Site-resolved contributions to show that the Fe2 sublattice contributes considerably to the overall uniaxial anisotropy in V1Fe2Se4, whereas the Se sublattice contribution shifts from planar anisotropy in Fe3Se4 to uniaxial. Such improvements in uniaxial MAE, together with improved structural stability, make V1Fe2Se4 a promising choice for rare-earth-free PMs.

Perpendicularly magnetized epitaxial Co/Ni multilayers grown on Ru(0001) layers by alternate monoatomic layer deposition

The hcp stacked Bh-ordered CoNi film was a candidate material to simultaneously have large uniaxial magnetic anisotropy energy (Ku) and a low Gilbert damping constant, which were previously predicted by a first-principles calculation. In this paper, we investigated the film growth condition to form the hcp stacked CoNi layers. [Co(1 ML)/Ni(1 ML)]N multilayers were epitaxially grown on Al2O3(11-20)/Ru(0001) underlayers by molecular beam epitaxy using an alternate monoatomic layer deposition technique with changing growth temperature (Ts) and repetition number (N). As the results of structural characterizations by x-ray diffraction measurements, it was found that the fcc- and hcp-CoNi phases were mixed in the samples, and the volume fraction of the fcc phase was larger than that of the hcp phase. However, the formation of the hcp-CoNi phase was promoted near the interface with the Ru layer having the hcp structure. The low growth temperature and the small N increased the volume fraction of the hcp phase. The Ku value of 5.1 Merg/cm3 was achieved for the [Co(1 ML)/Ni(1 ML)]20 multilayer grown at room temperature. In addition, a perpendicularly magnetized film was realized even for the thin sample with N = 5 (2 nm). This means that the Co/Ni multilayers are a thin ferromagnetic material suitable for application to spintronic devices.

Magneto-optical property and magnetic anisotropy of (100) oriented R0.5Bi2.5Fe5O12 (R = Eu, Sm, and Pr) thin films prepared by metal–organic decomposition

Bi-substituted rare-earth iron garnets, R3−xBixFe5O12 (Bi:RIG), where R represents one of the rare-earth elements, exhibit the excellent magneto-optical (MO) properties that increase with Bi content x. In addition, magnetic properties of Bi:RIGs, such as the magnetization, the magnetic anisotropy, and the magnetostriction, could be controlled by choosing rare-earth elements. In this paper, we report on R0.5Bi2.5Fe5O12 (Bi2.5:RIG, R = Pr, Sm, and Eu) thin films on Gd3Ga5O12 (GGG) (100) single crystal substrates prepared by the metal–organic decomposition method. XRD analysis reveals that Bi2.5:RIG thin films are grown along the same orientation with GGG substrates, and their lattice constants are dependent on the ionic radii of the rare-earth ions. MO measurements show that Faraday spectra of the Bi2.5:RIG thin films have a typical spectral structure observed for Bi:RIGs. The magnetic anisotropy constants, the uniaxial magnetic anisotropy energy Ku, and the magnetocrystalline anisotropy energy K1 of Bi2.5:RIG (R = Y, Pr, Nd, Sm, and Eu) thin films are investigated by using the ferromagnetic resonance measurement.

Origin of uniaxial magnetic anisotropy in MnAlCx: A first-principles study

Exploring the thermodynamically metastable L10-ordered τ-MnAl alloy and its intrinsic magnetic properties are of great importance for its potential candidature as rare-earth-free permanent magnets (PMs). Here, based on first-principles calculations, we present a comprehensive investigation of the intrinsic magnetic properties of MnAlCx. The interstitial C-doping is demonstrated to have a substantial influence on the uniaxial magnetic anisotropy energy Ku, making MnAlCx appealing for PM applications. We predict a substantial enhancement in Ku of up to 2.30 MJ/m3 for x = 1, which is roughly 35% larger than that of pristine MnAl. The atomic resolved and orbital resolved Ku, as well as the perturbation theory energy analysis, may be used to understand the cause of this enhancement. Using second-order perturbation theory and electronic structure analysis, we show that increased Ku is caused by a complex interplay between tetragonal and orbital distortion due to the C-doping. These findings can aid in the efficient and inexpensive design of PM materials.

Controlling domain wall thermal stability switching in magnetic nanowires for storage memory nanodevices

The domain wall (DW) random switching in planar magnetic nanowires is one of the crucial problems for storage data applications. Hence, a micromagnetic simulation was used to investigate the transverse domain wall (TDW) nucleation in the thinner and narrower nanomagnetic devices and the vortex domain wall (VDW) nucleation for the thicker and wider nanowires due to the device temperature. The TDW thermal creation was examined based on magnetic properties such as uniaxial magnetic anisotropy energy (Ku) and saturation magnetization (Ms). The thermal stability of TDW switching in nanowires is strongly dependent on the improvement of magnetic properties, whereas the TDW thermal nucleation decreases by increasing Ku or Ms. In addition, the TDW and VDW thermal creation in storage nanodevices such as nanowires could be controlled by nanowire geometry manipulation like width and thickness. Reducing the nanowire width or increasing its thickness helps both domain wall types (TDW and VDW) switching to be more stable against nanodevice temperature. TDW thermal switching was found to be stable under a device temperature of up to 500 K, which is higher than the room temperature. However, the VDW shows higher thermal stability switching reaches up to 900 k, which are good candidates for storage applications. Furthermore, the TDW dynamics in nanowires were affected by device temperature, whereas the TDW moves faster by increasing nanodevice temperature. All these findings will help to maintain the storage memory in nanodevices from failure due to device temperature.

Structural, Magnetic, and Electric Properties of Pt/Co/Au/Cr<sub>2</sub>O<sub>3</sub>/Pt Thin Film with Cr<sub>2</sub>O<sub>3</sub> Layer below 25 nm

Perpendicular exchange bias using magnetoelectric Cr2O3 has an electric-field triggered switching ability, and the thickness limit of the Cr2O3 layer for inducing this bias is a topic of research. In this paper, we investigated the structural, magnetic, and electric properties of Pt/Co/Au/Cr2O3/Pt thin films with a Cr2O3 layer in the thickness range of 5.7 to 25 nm. By using a magnetron sputtering method, a well-crystallized Cr2O3(0001) layer was formed in 5.7-nm-thick Cr2O3. All studied films showed perpendicular magnetic anisotropy. The uniaxial magnetic anisotropy energy density increased as the Cr2O3 thickness decreased, and 810±90 kJ/m3 was obtained for the film with 5.7-nm-thick Cr2O3. Perpendicular exchange bias was evaluated above 80 K, and an exchange anisotropy energy density of 0.30 mJ/m2 was observed for the film with a 25-nm-thick Cr2O3 at 80 K. The exchange bias could not be observed below 18 nm. Instead, coercivity enhancement, which yields the exchange bias by precisely controlling interfacial exchange coupling, was observed. The electric resistivity was about 5 × 105 Ωm for the 5.7-nm-thick Cr2O3 layer, which is sufficiently high for magnetoelectric applications.

Perpendicularly magnetized Ni/Pt (001) epitaxial superlattice

A perpendicularly magnetized ferromagnetic layer is an important building block for recent/future highdensity spintronic memory applications. This paper reports on the fabrication of perpendicularly magnetized Ni / Pt superlattices and the characterization of their structures and magnetic properties. The optimization of film growth conditions allowed us to grow epitaxial Ni / Pt (001) superlattices on SrTiO$_{3}$ (001) single crystal substrates. We investigated their structural parameters and magnetic properties as a function of the Ni layer thickness, and obtained a high uniaxial magnetic anisotropy energy of 1.9 x 10$^{6}$ erg/cm$^{3}$ for a [Ni (4.0 nm) / Pt (1.0 nm)] superlattice. In order to elucidate the detailed mechanism on perpendicular magnetic anisotropy for the Ni / Pt (001) superlattices, the experimental results were compared with the first-principles calculations. It has been found that the strain effect is a prime source of the emergence of perpendicular magnetic anisotropy.

Epitaxial L1-FeNi films with high degree of order and large uniaxial magnetic anisotropy fabricated by denitriding FeNiN films

L10-orderd FeNi alloy films with a high degree of order (S) and a large uniaxial magnetic anisotropy energy (Ku) were realized by denitriding FeNiN films. FeNiN films with the a-axis perpendicular to the film plane were epitaxially grown on SrTiO3 (001) substrates by molecular beam epitaxy by changing the growth temperatures (TS) to 200, 250, and 350 °C. The a-axis oriented epitaxial L10-FeNi films were fabricated by annealing the FeNiN films in a H2 gas atmosphere at 300 °C. S and Ku of the denitrided L10-FeNi films were characterized by anomalous x-ray diffraction using synchrotron radiation and magnetic torque measurements, respectively. A high S of 0.87 and a Ku of 5.9 × 105 J/m3 were realized in the L10-FeNi film with a TS of 350 °C. This high S value exceeds the values reported on L10-FeNi to date, but the Ku value was comparable to those of c-axis oriented L10-FeNi films with S ∼ 0.5 grown by alternate monoatomic deposition of Fe and Ni layers. A possible origin for the suppressed macroscopic Ku in a-axis oriented L10-FeNi films is discussed, and denitriding FeNiN is a promising method for the fabrication of L10-FeNi with a high S and a large Ku.

Strain-promoted perpendicular magnetic anisotropy in Co–Rh alloys

We report on a comprehensive experimental, numerical, and computational investigation on the concentration dependence of the structural/magnetic properties of Co–Rh alloy films. A sizable perpendicular magnetic anisotropy is achieved by controlling the lattice strain via the Co content. Within the 30–40% range of Co concentrations, an experimental effective magnetic anisotropy on the order of 100 kJ/m3 and a computational uniaxial magnetic anisotropy energy of 567 μeV/atom have been observed. First-principles calculations revealed that the lattice strain promotes a strong d-orbital degeneracy near the Fermi level for 40% of Co concentration, leading to an enhanced magnetic anisotropy energy.

Large magnetic anisotropy in highly strained epitaxial MgFe2O4 thin films

In order to acquire a soft magnetic film with low conductivity and large magnetic anisotropy, the strain-modulated magnetic anisotropy is studied in epitaxial MgFe2O4 (MFO) films. The MFO films with thicknesses of 25, 48, 75, and 110 nm are grown on the MgAl2O4 (MAO) (100) substrate using a pulsed laser deposition technique. Due to the large lattice-mismatch (3.34%) between MFO and MAO substrates, the interface exhibits a large tetragonal compressive strain. The results of field-dependent magnetization suggest the soft magnetic nature of all the measured MFO films. The analysis of angular dependent ferromagnetic resonance reveals the large uniaxial magnetic anisotropy energy (Ku) of −1.62 × 106 erg/cm3 in the highly strained 25 nm film, and Ku decreases with the increasing thickness due to strain relaxation. The observed large magnetic anisotropy in these highly strained MFO thin films is larger than most of the soft ferrite thin films, which arise due to tetragonal distortion and inverse magnetostriction. The epitaxial MFO thin films with enhanced magnetic anisotropy could be one of the potential candidates for spin filters.

Perpendicularly magnetized Cu2Sb type (Mn-Cr)AlGe films onto amorphous SiO2

Element substitution effects on the crystal structure and magnetic properties are investigated by substituting Cr atoms for a part of Mn-sites in the Cu2Sb-type MnAlGe. Perpendicularly magnetized (001)-textured films were successfully fabricated onto thermally oxidized silicon substrates without underlayers for the Cr-concentration ranging from 0 to 0.45 in the stoichiometry. The uniaxial magnetic anisotropy energy, Ku is enhanced by Cr-substitution, and the maximum value is 7.3 × 106 erg cm−3 at room temperature. The enhancement of Ku can be explained by the change of electronic structure due to Cr-substitution, based on the second order perturbation theory with spin-orbit interaction.

Strain mediated asymmetric response of the cation distribution on epitaxial CoFe2O4 films

The asymmetric response of the cation distribution on [001] oriented CoFe2O4 films were examined. Depending on the deposition temperature and substrates (MgO(0 0 1) or SrTiO3(0 0 1)), the films exhibited a range of compressive or tensile strain states along the out-of-plane. With increases in deposition temperature, the initial compressive (tensile) strain for the films grown on MgO(0 0 1) (SrTiO3(0 0 1)) was reduced. Furthermore, the out-of-plane (in-plane) magnetic anisotropy of the film grown on MgO(0 0 1) (SrTiO3(0 0 1)) decreased with increasing deposition temperature. The uniaxial magnetic anisotropy energy calculation based on the magnetic anisotropy (crystalline and shape) and strain of films confirmed that the strain reduction with increasing deposition temperature is the main source of the uniaxial magnetic anisotropy reduction, regardless of the sign of the strain. X-ray photoelectron spectroscopy explained the saturation magnetization variation by the cation distribution depending on the strain state. Furthermore, the calculated magnetic moment based on the cation distribution were well matched for the high crystalline films.

Uniaxial magnetic anisotropy energy of bimetallic Co-Ni clusters from a first-principles perspective.

Along with the growing precision in the control of matter at increasingly smaller size scales, a field of research, based onto magnetic materials of technical interest, such as bimetallic clusters, has been developed in very recent years. Thereby, here, we report on a complete study of bimetallic clusters composed of cobalt and nickel with up to 7 atoms using ab initio methods in the GGA approach. We applied an unrestricted search method based on the tensor of inertia eigenvalues to find the most stable configurations of the clusters, obtaining a diverse set of structures with different geometric properties. We explored the effect of composition on the structural properties, the chemical stability, the magnetization and the magnetic anisotropy energy (MAE) of the so-obtained systems. Our results indicate that the behavior of the clusters is mainly governed by the Co-Co interaction and to a lesser extent by the Co-Ni and Ni-Ni interactions. Furthermore, for a given cluster size the magnetic moment increases by 2 μB/Co-substitution plus 1 μB/Ni-substitution coming from the cobalt and nickel core d-states, while in some cases unpaired hybrid s-electrons can also give rise to itinerant magnetism. These features have been analyzed with the help of a Jellium model and have important consequences for the magnetism and the magnetic anisotropy of the clusters. The magnetic behavior and MAE present complex and intriguing landscapes, which suggests the possibility of finely controlling the magnetic states, by tuning the cluster composition, aiming at technical implementation in fields such as molecular magnetism or quantum computation. In particular, cases such as Co6Ni, Co4Ni3, CoNi6 Co2Ni5 and Co3Ni3 present high relative stability and enhanced magnetic moments (around 10 μB), what makes them promising candidates for applications such as subnanometer magnetic information storage.

Magnetic characteristics and nanostructures of FePt granular films with GeO2 segregant

To realize a granular film composed of L10-FePt grains with high uniaxial magnetic anisotropy energy, Ku, and segregants for energy-assisted magnetic recording, a FePt-GeO2/FePt-C stacked film was investigated in the engineering process. The FePt-GeO2/FePt-C stacked film fabricated at a substrate temperature of 450 °C realized uniaxial magnetic anisotropy, Kugrain, of about 2.5 × 107 erg/cm3, which is normalized by the volume fraction of FePt grains, and a granular structure with an averaged grain size of 7.7 nm. As the thickness of the FePt-GeO2 upper layer was increased to 9 nm, the Ku values were almost constant. That result differs absolutely from the thickness dependences of the other oxide segregant materials such as SiO2 and TiO2. Such differences on the oxide segregant are attributed to their chemical bond. The strong covalent bond of GeO2 is expected to result in high Ku of the FePt-GeO2/FePt-C stacked films.

PdSb添加L1<sub>0</sub>-FePt系薄膜の結晶配向性および磁気特性

FePt thin films with L10 ordered structure are candidates for high-density magnetic recording media because of their high uniaxial magnetic anisotropy energy. The (Fe0.395Pt0.395Cu0.15P0.02Pd0.04)100–xSbx thin films with various x were deposited directly on quartz glass substrates by a sputtering method. FePt ordered alloy thin films with (001) preferential orientation were achieved in Sb content of x ≥ 8.0 at.% with post-annealing at 600°C for 1 hour under reduced pressure in a H2 atmosphere. However, the coercivity of these thin films decreased dramatically due to growing of the crystal grains. Therefore, in this study, we prepared the PdSb-FePt-(C4F8)n granular thin films to improve the coercivity. The Fe0.44Pt0.44Pd0.04Sb0.08-(C4F8)n granular thin film deposited at C4F8 partial pressure of 0.1 mTorr then annealed at 700°C for 1 hour under reduced pressure in a H2 atmosphere exhibited a large coercivity of 30 kOe.

Stress-induced large anisotropy field modulation in Ni films deposited on a flexible substrate

A tensile strain on the order of a few percent was created in Ni thin films deposited on a flexible polyethylene naphthalate substrate, and the strain-induced change in the magnetic anisotropy was investigated. The magnetic easy axis was reversibly switched by 90° by the application of the stress. The easy axis was orthogonal to the applied stress. The in-plane saturation magnetic field or the uniaxial magnetic anisotropy energy changed linearly in reaction to the applied tensile strain up to a strain of 2.3%. Moreover, a large difference in the saturation magnetic field up to ∼0.3 T, which corresponds to a change in the magnetic anisotropy energy of ∼7 × 104 J/m3, was realized. The effective magnetoelastic coupling constant was almost independent of the thickness of Ni.