Anisotropy Of Orbital Magnetic Moment Research Articles

Investigating Magnetocrystalline Anisotropy in the System Au/Co-Staircase/Au(788) by Using XMCD

Here, we report the investigation of the influence of the magnetocrystalline anisotropy (MCA) in Cobalt ultrathin films grown on the vicinal surface Au(788), through the anisotropy of the orbital magnetic moment. The aim of this study was to apply the X-ray magnetic circular dichroism (XMCD) technique to probe the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">spin</i> magnetic moment and the orbital magnetic moment anisotropy within the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">spin</i> reorientation transition (SRT) range in the system Au/Co-Staircase/Au(788). The influence of increasing Co film thickness on SRT, from easy out-of-plane magnetization axis to in-plane magnetization was investigated by means of the magneto-optical <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Kerr</i> effect (MOKE). The preparation and surface quality of the Co films were characterized using LEED and STM. Analysis of XMCD measurements as a function of the film thickness for Au/Co-staircase/Au(788) reveals the anisotropic orbital magnetic moment during the SRT regime (8 to 12 ML range) indicating a decreasing influence of MCA with the increased thickness and nearly isotropic orbital magnetic moment above 12 ML, with a small MCA influence.

Effect of chemical disorder on the magnetic anisotropy in L10 FeNi from first-principles calculations

We use first-principles calculations to investigate how deviations from perfect chemical order affect the magnetocrystalline anisotropy energy (MAE) in $L{1}_{0}$ FeNi. We first analyze the local chemical environment of the Fe atoms in various partially ordered configurations, using the orbital magnetic moment anisotropy (OMA) as proxy for a local contribution to the MAE. We are able to identify a specific nearest neighbor configuration and use this ``favorable environment'' to successfully design various structures with MAE higher than the perfectly ordered system. However, a systematic analysis of the correlation between local environment and OMA using smooth overlap of atomic positions indicates only a partial correlation, which exists only if the deviation from full chemical order is not too large, whereas in general no such correlation can be identified even using up to third nearest neighbors. Guided by the observation that the identified favorable environment implies an Fe-rich composition, we investigate the effect of randomly inserting additional Fe into the nominal Ni planes of the perfectly ordered structure. We find that the MAE increases with Fe content, at least up to 62.5% Fe. Thus, our paper shows that the perfectly ordered case is not the one with highest MAE and that an increased MAE can be obtained for slightly Fe-rich compositions.

Control of perpendicular magnetic anisotropy at the Fe/MgO interface by phthalocyanine insertion

Perpendicular magnetic anisotropy at an interface between Fe and MgO with Co-phthalocyanine (CoPc) adsorption has been investigated. We find that the CoPc adsorption at an Fe/MgO interface increases the perpendicular magnetic anisotropy energy (PMA) while maintaining the voltage-controlled magnetic anisotropy effect. By performing x-ray magnetic circular dichroism spectroscopy measurements, we reveal that the CoPc adsorption induces hole accumulation at the Fe surface. The origin of the PMA enhancement is attributed to the increased orbital magnetic moment anisotropy of the Fe atoms.

Interplay between chemical order and magnetic properties in L10 FeNi (tetrataenite): A first-principles study

We use first-principles-based calculations to investigate the interplay between chemical order and the magnetic properties of $L1_0$ FeNi. In particular, we investigate how deviations from perfect chemical order affect the energy difference between the paramagnetic and ferromagnetic states as well as the important magneto-crystalline anisotropy energy. Our calculations demonstrate a strong effect of the magnetic order on the chemical order-disorder transition temperature, and conversely, a strong enhancement of the magnetic transition temperature by the chemical order. Most interestingly, our results indicate that the magnetic anisotropy does not decrease significantly as long as the deviations from perfect order are not too large. Moreover, we find that in certain cases a slight disorder can result in a higher anisotropy than for the fully ordered structure. We further analyze the correlation between the magneto-crystalline anisotropy and the orbital magnetic moment anisotropy, which allows to study the effect of the local chemical environment on both quantities, potentially enabling further optimization of the magneto-crystalline anisotropy with respect to chemical order and stoichiometric composition.

Correlation between tetragonal zinc-blende structure and magnetocrystalline anisotropy of MnGa epilayers on GaAs(111)

Abstract MnGa films of few nanometer thickness with tetragonal zinc-blende (TZB) structure were grown by molecular beam epitaxy on GaAs(111) substrates. These ultrathin films have high magnetization at room temperature with magnetic moment as high as 3.2 μ B per formula unit. A strong magnetocrystalline anisotropy energy (MAE) comparable to that reported to δ -MnGa films with body-centered tetragonal (BCT) structure with similar c / a =1.1 is observed. Electronic structure calculations using density functional theory (DFT) reveal a robust ferrimagnetic ground state at room temperature and confirm that zinc-blende structure with tetragonal distortion has a metastable character. The strong MAE is associated with anisotropy of orbital magnetic moment which is described by the symmetry of the spin-polarized charge density along the crystallographic axes.

First principles calculations, neutron, and x-ray diffraction investigation of Y3Ni13B2, Y3Co13B2, and Y3Ni10Co3B2

Fully relativistic calculations within the local spin density approximation and the generalized gradient approximation were performed to determine the local spin and orbital magnetic moments, as well as the magnetocrystalline anisotropy energy of Y3Ni13B2, Y3Co13B2, and Y3Ni10Co3B2 compounds. A weak in-plane magnetic anisotropy is determined for Y3Ni13B2, under the assumption of a crystallographic-like magnetic unit cell and collinear magnetic moments. The calculations predict considerable c-axis anisotropy for Y3Co13B2 and Y3Ni10Co3B2, but smaller than that of YCo5. The values of the magnetocrystalline anisotropy energy correlate well with both the magnitude of the orbital magnetic moment and the orbital magnetic moment anisotropy. The mixing between Co or Ni 3d states and B 2p states, observable at the bottom of the valence band of the 3d metal having a boron atom nearest neighbor, decreases the 3d spin and especially, the 3d orbital magnetic moments. Y3Ni13B2 and Y3Ni10Co3B2 were also investigated by powder neutron diffraction experiments, at temperatures between 1.8 and 249 K. The Co and Ni site averaged magnetic moments calculated in the mixed compound are in fair agreement with the values obtained by the refinement of the magnetic contribution to the diffraction pattern.

In-plane magnetocrystalline anisotropy observed on Fe/Cu(111) nanostructures grown on stepped surfaces

Magnetic in-plane and out-of-plane anisotropies measured by angle dependent x-ray magnetic circular dichroism (XMCD) on fcc Fe nanostructures are discussed and compared with fcc FeNi nanostructures. All studies were performed using XMCD at the Fe ${L}_{2,3}$ edges for Fe grown on a Cu(111) vicinal vic surface. The step induced in-plane anisotropy in the step decoration regime is analyzed by measuring the orbital magnetic moment dependence as a function of the in-plane azimuth and out-of-plane incidence angles. In the one-dimensional limit where the out-of-plane magnetic easy axis dominates, Fe/Cu(111) shows a large in-plane orbital magnetic moment anisotropy leading to a magnetocrystalline anisotropy energy of 0.4 meV/atom and an in-plane magnetic easy axis perpendicular to the steps. In the nanometer scale the aspect ratio of the elongated rectangular Fe stripes are found to be responsible for the in-plane and out-of-plane anisotropy. This is coherent with previous findings where the circular shaped fcc ${\mathrm{Fe}}_{0.65}{\mathrm{Ni}}_{0.35}$ nanostructures do not show any in-plane anisotropy. The three-dimensional nanostructures are characterized by magnetic orbital moments connected with the number of broken bonds in the direction of the quantization axis defined by the direction of the saturation field. The microscopic origin of the in-plane large orbital magnetic moment anisotropy is attributed to the nanometer size of the structures perpendicular to the steps and to the asymmetry of the number of broken bonds in the plane.

Interface magnetism in ultrathin Fe/W(110) films from first principles

An ab initio study of the magnetic properties of Fe ultrathin films on top of a W(110) substrate shows that for one Fe layer the magnetization axis is in-plane. For an additional layer of Fe, the magnetosurface and magnetoelastic anisotropies favor a magnetization axis perpendicular to the substrate, but the total energy including the shape anisotropy is minimal for the spin axis in-plane. In the case of the trilayer film all anisotropies favor an in-plane magnetization axis. The spin magnetic moment of the first Fe atomic layer is close to the bulk value while that of the second and third Fe atomic layers are considerably increased. The W atoms at the interface are weakly antiferromagnetically coupled to Fe. The orbital magnetic moment anisotropy of all the atoms is shown to be directly related to the calculated x-ray magnetic circular dichroism anisotropy.

Relativistic spin-polarized theory of magnetoelastic coupling and magnetic anisotropy strain dependence: Application to Co/Cu(001)

A self-consistent relativistic spin-polarized version of the total-energy full-potential linearized-augmented-plane-wave (FLAPW) method is developed on the basis of a second-variation treatment of the spin-orbit coupling (SOC). As illustration, the method is applied to determine the magnetoelastic coupling, orbital magnetic moment anisotropy and magnetic anisotropy energy (MAE) of a Co overlayer on Cu(001). The MAE (-0.36 meV) calculated at the equilibrium overlayer/substrate distance is in good agreement with experiment. As discovered earlier by Wu and Freeman, we find a linear dependence of the MAE on the overlayer/substrate distance. The calculated positive effective magnetoelastic coupling coefficient (1.13 meV) is caused by a positive surface magnetoelastic anisotropy (0.23 meV). This causes a negative magnetostriction coefficient ${\ensuremath{\lambda}}_{001}=\ensuremath{-}5.20\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}$ and an isotropic magnetostriction coefficient ${\ensuremath{\lambda}}_{s}=\ensuremath{-}5.65\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}$ that is in very good agreement with previous studies based on a perturbative SOC treatment.