Ultra-thin film of FeRh on insulator MgO substrate has been investigated usingab-initio electronic structure calculations. From this calculation, we have found the interesting effect of epitaxial strain on the magnetocrystalline anisotropy (MCA). Analysis of the energy and k-resolved distribution of the orbital character of the band structure reveals that MCA largely arises from the spin-orbit coupling (SOC) between dx2-y2 andd xz,yz orbitals of Fe atoms at the FeRh/MgO interface. We demonstrate that the strain has significant effects on the MCA: It not only affects the value of the MCA but also induces a switching of the magnetic easy axis from perpendicular to in-plane direction. The mechanism is the strain-induced shifts of the SOC d-states. Our work demonstrates that strain engineering can open a viable pathway towards tailoring magnetic properties for antiferromagetic spintronic applications.
Rh-terminated FeRh(001) film is known to be stable in a ferromagnetic (FM) state different from a G-type antiferromagnetic (G-AFM) bulk ground state, while an Fe-terminated FeRh(001) film has the same ground state as the bulk. In this paper, we investigate the magnetic properties of asymmetrically terminated FeRh(001) films: one surface is Fe-terminated and the other is Rh-terminated. Rh surface only ] (RhSO) FM state in asymmetrically terminated FeRh(001) film is identified to exhibit 40% increased perpendicular MCA energy as compare to that of the whole-layer (WL) FM state. This increased MC…
Magnetism of FeRh (001) films strongly depends on film thickness and surface terminations. While magnetic ground state of bulk FeRh is G-type antiferromagnetism, the Rh-terminated films exhibit ferromagnetism with strong perpendicular MCA whose energy +2.1 meV/$\Box$ is two orders of magnitude greater than 3$d$ magnetic metals, where $\Box$ is area of two-dimensional unit cell. While Goodenough-Kanamori-Anderson rule on the superexchange interaction is crucial in determining the magnetic ground phases of FeRh bulk and thin films, the magnetic phases are results of interplay and competition bet…
Magnetic phase transition tunnel magnetoresistance (MPT-TMR) effect with a single magnetic electrode has been investigated by first-principles calculations. The calculations show that the MPT-TMR of FeRh/MgO/Cu tunnel junction can be as high as hundreds of percent when the magnetic structure of FeRh changes from G-type antiferromagnetic (GAFM) to ferromagnetic order. This new type of MPT-TMR may be superior to the tunnel anisotropic magnetoresistance because of its huge magneto-resistance effect and similar structural simplicity. The main mechanism for the giant MPT-TMR can be attributed to th…
Phenomena originated from spin-orbit interaction, such as magnetic anisotropy (MA), Rashba-type interactions, or topological insulators, have drawn huge attention for its intriguing physics. In particular, the search for a novel antiferromagnetic material, with potentially large perpendicular MA (PMA), has been becoming very intensive for next-generation high density memory applications. Here, we propose that substitutions of transition metals Ru and Ir, neighboring and same group elements in the periodic table, for the Rh site in the vicinity of surface can induce a substantially large PMA, u…
Propagation of laser-generated GHz surface acoustic wavepackets in FeRh/MgO(001) below and above the antiferromagnetic-ferromagnetic phase transition
Ioffe Institute（约费研究所）；P.N. Lebedev Physical Institute of the RAS（俄罗斯科学院列别捷夫物理研究所）；Institute of Metal Physics of the Ural Branch of the RAS（俄罗斯科学院乌拉尔分支金属物理研究所）；Lomonosov Moscow State University（莫斯科国立罗蒙诺索夫大学）
The origin of large perpendicular magneto-crystalline anisotropy (PMCA) in Fe/MgO (001) is revealed by comparing Fe layers with and without the MgO. Although Fe-O $p$-$d$ hybridization is weakly present, it cannot be the main origin of the large PMCA as claimed in previous study. Instead, perfect epitaxy of Fe on the MgO is more important to achieve such large PMCA. As an evidence, we show that the surface layer in a clean free-standing Fe (001) dominantly contributes to $E_{MCA}$, while in the Fe/MgO, those by the surface and the interface Fe layers contribute almost equally. The presence of …
The antiferromagnetic (AFM) to ferromagnetic (FM) first order phase transition of an epitaxial FeRh thin-film has been studied with x-ray magnetic circular dichroism using photoemission electron microscopy. The FM phase is magnetized in-plane due to shape anisotropy, but the magnetocrystalline anisotropy is negligible and there is no preferred in-plane magnetization direction. When heating through the AFM to FM phase transition the nucleation of the FM phase occurs at many independent nucleation sites with random domain orientation. The domains subsequently align to form the final FM domain st…
Antiferromagnets with tunable phase transitions are promising for future spintronics applications. We investigated spin-dependent transport properties of FeRh thin films, which show a temperature driven antiferromagnetic-to-ferromagnetic phase transition. Epitaxial FeRh films grown on MgO (001) substrates exhibit a clear magnetic and electronic phase transition. By performing anomalous Hall and anomalous Nernst effect measurements over a wide range of temperatures, we demonstrate that the thermally driven transition shows distinctly different transverse transport on both side of the phase tran…
Magnetocrystalline anisotropy at Heusler alloy$|$MgO interfaces have been studied using first principles calculations. It is found that Co terminated Co$_{2}$FeAl$|$MgO interfaces show perpendicular magnetic anisotropy up to 1.31 mJ/m$^2$, while those with FeAl termination exhibit in-plane magnetic anisotropy. Atomic layer resolved analysis indicates that the origin of perpendicular magnetic anisotropy in Co$_{2}$FeAl$|$MgO interfaces can be attributed to the out-of-plane orbital contributions of interfacial Co atoms. At the same time, Co$_{2}$MnGe and Co$_{2}$MnSi interfaced with MgO tend to …
Density-functional calculations are performed to explore magnetoelectric effects originating from the influence of an external electric field on magnetic properties of the Fe/MgO(001) interface. It is shown that the effect on the interface magnetization and magnetocrystalline anisotropy can be substantially enhanced if the electric field is applied across a dielectric material with a large dielectric constant. In particular, we predict an enhancement of the interface magnetoelectric susceptibility by a factor of the dielectric constant of MgO over that of the free standing Fe (001) surface. We…
Least absolute shrinkage and selection operator (Lasso) was originally formulated for least squares models and this simple case reveals a substantial amount about the behavior of the estimator. It also shows that the coefficient estimates need not be unique if covariates are collinear. Using this Lasso technique, we analyze a magnetocrystalline anisotropy energy which is a long-standing issue in transition-metal thin films, expectially for Fe-Rh thin film systems on a MgO substrate. Our LASSO regression took advantage of the data obtained from first principles calculations for single slabs wit…
Spintronics exploits the magnetoresistance effects to store or sense the magnetic information. Since the magnetoresistance strictly depends on the magnetic anisotropy of the system, it is fundamental to set a defined anisotropy to the system. Here, we investigate by means of vectorial Magneto-Optical Kerr Magnetometry (v-MOKE), half-metallic La0.67Sr0.33MnO3 (LSMO) thin films that exhibit at room temperature pure biaxial magnetic anisotropy if grown onto MgO (001) substrate with a thin SrTiO3 (STO) buffer. In this way, we can avoid unwanted uniaxial magnetic anisotropy contributions that may b…
We present the fascinating magnetic properties in homogenous noble-metal-free and rare-earth-free L10-Mn1.5Ga epitaxial films on GaAs (001), including ultrahigh perpendicular coercivity remarkably tunable from 8.1 to 42.8 kOe, giant perpendicular magnetocrystalline anisotropy with a maximum of 22.9 Merg/cc, easily controllable magnetization from 27.3 to 270.5 emu/cc, excellent squareness exceeding 0.94 and large magnetic energy product up to 2.6 MGOe. These magnificent room-temperature magnetic characteristics make our L10-Mn1.5Ga films multifunctional as outstanding and cost-effective alterna…
We study interfacial magnetocrystalline anisotropies in various Fe/semiconductor heterostructures by means of first-principles calculations. We find that many of those systems show perpendicular magnetic anisotropy (PMA) with a positive value of the interfacial anisotropy constant $K_{\rm i}$. In particular, the Fe/CuInSe$_2$ interface has a large $K_{\rm i}$ of $\sim 2.3\,{\rm mJ/m^2}$, which is about 1.6 times larger than that of Fe/MgO known as a typical system with relatively large PMA. We also find that the values of $K_{\rm i}$ in almost all the systems studied in this work follow the we…
Understanding magnetocrystalline anisotropy (MCA) is fundamentally important for developing novel magnetic materials. Therefore, clarifying the relationship between MCA and local physical quantities observed by spectroscopic measurements, such as the orbital and quadrupole moments, is necessary. In this review, we discuss MCA and the distortion effects in magnetic materials with transition metals (TMs) based on the orbital and quadrupole moments, which are related to the spin-conserving and spin-flip terms in the second-order perturbation calculations, respectively. We revealed that orbital mo…
We study the tunnel magnetoresistance (TMR) effect and magnetocrystalline anisotropy in a series of magnetic tunnel junctions (MTJs) with $L1_1$-ordered fcc ferromagnetic alloys and MgO barrier along the [111] direction. Considering the (111)-oriented MTJs with different $L1_1$ alloys, we calculate their TMR ratios and magnetocrystalline anisotropies on the basis of the first-principles calculations. The analysis shows that the MTJs with Co-based alloys (CoNi, CoPt, and CoPd) have high TMR ratios over 2000$\%$. These MTJs have energetically favored Co-O interfaces where interfacial antibonding…
We present a theoretical study on interfacial magnetocrystalline anisotropy for Fe/MgAl$_2$O$_4$. This system has a very small lattice mismatch at the interface and therefore is suitable for realizing a fully coherent ferromagnet/oxide interface for magnetic tunnel junctions. On the basis of density functional theory, we calculate the interfacial anisotropy constant $K_{\rm i}$ and show that this system has interfacial perpendicular magnetic anisotropy (PMA) with $K_{\rm i} \approx 1.2\,{\rm mJ/m^2}$, which is a little bit smaller than that of Fe/MgO ($K_{\rm i} \approx$ 1.5--1.7$\,{\rm mJ/m^2…
Voltage controlled magnetic anisotropy (VCMA) is an efficient way to manipulate the magnetization states in nanomagnets, promising for low-power spintronic applications. The underlying physical mechanism for VCMA is known to involve a change in the d-orbital occupation on the transition metal interface atoms with an applied electric field. However, a simple qualitative picture of how this occupation controls the magnetocrystalline anisotropy (MCA) and even why in certain cases the MCA has opposite sign still remains elusive. In this paper, we exploit a simple model of orbital populations to el…
The influence of epitaxial strain on uniaxial magnetic anisotropy of Co$_{2}$FeSi (CFS) and Co$_{2}$MnSi (CMS) Heusler alloy thin films grown on (001) SrTiO$_3$ (STO) and MgO is reported. The in-plane biaxial strain is susceptible to tune by varying the thickness of the films on STO, while on MgO the films show in-plane easy axis for magnetization (\overrightarrow{M}) irrespective of their thickness. A variational analysis of magnetic free energy functional within the Stoner-Wohlfarth coherent rotation model with out-of-plane uniaxial anisotropy for the films on STO showed the presence of magn…
We investigate the effect of atomic ordering on the magnetic anisotropy of Ni80Fe20 at.% (Py). To this end, Py films were grown epitaxially on MgO (001) using dc magnetron sputtering (dcMS) and high power impulse magnetron sputtering (HiPIMS). Aside from twin boundaries observed in the latter case, both methods present high quality single crystals with cube-on-cube epitaxial relationship as verified by the polar mapping of important crystal planes. However, X-ray diffraction results indicate higher order for the dcMS deposited film towards L12 Ni3Fe superlattice. This difference can be underst…
