We report the observation of a compensation point in the temperature dependence of magnetization data of polycrystalline Sm2Al. Magnetization measurements show that this compound magnetically orders at about 150 K. Below this temperature, the magnetization data shows a compensation point, which shifts with field. Hysteresis loops obtained below the compensation temperature show that the compound possesses exchange anisotropy. Both the exchange anisotropy field and the coercive field are found to be quite large and comparable to those of the classical spin-orbit compensated ferromagnet (Sm,Gd)Al2. The heat capacity data also suggest that there are similarities between (Sm,Gd)Al2 and Sm2Al.
Magnetic droplet soliton is a localized dynamic spin state which can serve as a nanoscale information carrier and nonlinear oscillator. The present opinion is that the formation of droplet solitons requires the compensation of magnetic damping by a torque created by a spin-polarized electric current or pure spin current. Here we demonstrate theoretically that nanoscale droplet solitons can be generated and routed in ferromagnetic nanostructures with voltage-controlled magnetic anisotropy in the presence of uncompensated magnetic damping. Performing micromagnetic simulations for the MgO/Fe/MgO …
We have studied a spin-1/2, ABA, Ising trilayer system with two different types of interactions, in-plane ferromagnetic and out-of-plane anti-ferromagnetic, among the lattice sites, on different layers. In the pure case, devoid of any impurity, we employed Monte-Carlo method with single spin-flip Metropolis algorithm to find out the anti-ferromagnetic critical temperature (Néel temperature) and another lower temperature, called the compensation temperature, both with total magnetisation zero, in accordance with already established results for square lattice. Then non-magnetic impurities, (spin…
We examined what interactions control the sign and strength of the interlayer coupling in van der Waals ferromagnets such as Fe3-xGeTe2, Cr2Ge2Te6, CrI3 and VI3, to find that high-spin orbital interaction across the van der Waals gaps are a key to understanding their ferromagnetism. Interlayer ferromagnetic coupling in Fe3-xGeTe2 Cr2Ge2Te6, and CrI3 is governed by the high-spin two-orbital two-electron destabilization, but that in VI3 by the high-spin four-orbital two-electron stabilization. These interactions explain a number of seemingly puzzling observations in van der Waals fer-romagnets.
Inverse orbital Hall effect induced terahertz emission enabled by a ferromagnet with quenched orbital moment in Fe/Pt/W trilayers
Shaanxi University of Technology（陕西理工大学）；Fudan University（复旦大学）；Shanghai Research Center for Quantum Sciences（上海量子科学研究中心）；The Chinese University of Hong Kong, Shenzhen（香港中文大学（深圳））
A major challenge in spin-based electronics is reducing power consumption for magnetization switching of ferromagnets, which is being implemented by injecting a large spin-polarized current. The alternative approach is to control the magnetic anisotropy (MA) of the ferromagnet by an electric field. However, the voltage-induced MA is too weak to deterministically switch the magnetization without an assisting magnetic field, and the strategy towards this goal remains elusive. Here, we demonstrate a new scheme of orbital-controlled magnetization switching (OCMS): A sharp change in the MA is induc…
Compensated ferrimagnets, like antiferromagnets, show no net magnetization but their transport and magneto-optic properties resemble those of ferromagnets, thereby creating opportunities for applications in high-frequency spintronics and low-energy loss communications. Here we study the modification the noncollinear ferrimagnetic spin structure of Mn4N by a variety of metallic substitutions Z (Z = Cu - Ge and Ag - Sn) to achieve compensation at room temperature. The noncollinear frustrated 2.35 Bohr magneton moments of Mn on 3c sites of the (111) kagome planes tilt about 20 degree out-of-plane…
We report on the Dzyaloshinskii-Moriya (DMI) interaction at the interface between a ferromagnet and an oxide. We demonstrate experimentally that oxides can give rise to DMI. By comparison of systems comprised of Pt/Co90Fe10/Oxide and Cu/Co90Fe10/Oxide, we also show how oxidation of one interface can enhance and add to the total DMI of that generated by the Pt interface. This is due to the fact that the DMI on both interfaces promotes left-handed chirality. Finally, by use of ferromagnetic resonance spectroscopy, we show that the DMI and the spectroscopic splitting factor, which is a measure of…
In atomic physics, the Hund rule says that the largest spin and orbital state is realized due to the interplay of the spin-orbit coupling (SOC) and the Coulomb interactions. Here, we show that in ferromagnetic solids the effective SOC and the orbital magnetic moment can be dramatically enhanced by a factor of $1/[1-(2U^\prime-U-J_H)ρ_0]$, where $U$ and $U^\prime$ are the on-site Coulomb interaction within the same oribtals and between different orbitals, respectively, $J_H$ is the Hund coupling, and $ρ_0$ is the average density of states. This factor is obtained by using the two-orbital as wel…
The magnetic spin Hall effect (MSHE) is an anomalous charge-to-spin conversion phenomenon which occurs in ferromagnetic materials. In contrast to the conventional spin Hall effect (SHE), being a time-reversal even effect, the magnetic counterpart is time-reversal odd. In this work, we use ab initio calculations to investigate the MSHE for the bulk ferromagnets Fe, Co, and Ni. The magnitudes of the MSHE of Fe and Co are comparable to those of the SHE, but the MSHE is strongly dependent on the electron lifetime and the MSHE and SHE can moreover have opposite signs. For Ni the MSHE is smaller tha…
We report the observation of a unidirectional magnetoresistance (UMR) that originates from the nonequilibrium orbital momentum induced by an electric current in a naturally oxidized Cu/Co bilayer. The orbital-UMR scales with the torque efficiency due to the orbital Rashba-Edelstein effect upon changing the Co thickness and temperature, reflecting their common origin. We attribute the UMR to orbital-dependent electron scattering and orbital-to-spin conversion in the ferromagnetic layer. In contrast to the spin-current induced UMR, the magnon contribution to the orbital-UMR is absent in thin Co …
Fe3-xGeTe2 is a layered magnetic van der Waals material of interest for both fundamental and applied research. Despite the observation of intriguing physical properties, open questions exist even on the basic features related to magnetism: is it a simple ferromagnet or are there antiferromagnetic regimes and are the moments local or itinerant. Here, we demonstrate that antiferromagnetic spin fluctuations coexist with the ferromagnetism through comprehensive elastic and inelastic neutron scattering and thermodynamic measurements. Our realistic dynamical mean-field theory calculations reveal tha…
We show that even when spins and orbitals disentangle in the ground state, spin excitations are renormalized by the local tuning of $e_g$ orbitals in ferromagnetic planes of K$_2$CuF$_4$ and LaMnO$_3$. As a result, dressed spin excitations (magnons) obtained within the electronic model propagate as quasiparticles and their energy renormalization depends on momentum ${\vec k}$. Therefore magnons in spin-orbital systems go beyond the paradigm of the effective Heisenberg model with nearest neighbor spin exchange derived from the ground state --- spin-orbital entanglement in excited states predict…
Charged particles exhibit the Hall effect in the presence of magnetic fields. Analogously, ferromagnetic skyrmions with non-zero topological charges and finite fictitious magnetic fields exhibit the skyrmion Hall effect, which is detrimental for applications. The skyrmion Hall effect has been theoretically predicted to vanish for antiferromagnetic skyrmions because the fictitious magnetic field, proportional to net spin density, is zero. We experimentally confirm this prediction by observing current-driven transverse elongation of pinned ferrimagnetic bubbles. Remarkably, the skyrmion Hall eff…
The concepts of Weyl fermions and topological semimetals emerging in three-dimensional momentum space are extensively explored owing to the vast variety of exotic properties that they give rise to. On the other hand, very little is known about semimetallic states emerging in two-dimensional magnetic materials, which present the foundation for both present and future information technology. Here, we demonstrate that including the magnetization direction into the topological analysis allows for a natural classification of topological semimetallic states that manifest in two-dimensional ferromagn…
At ambient pressure, bulk SrCoO$_{3}$ is a ferromagnetic (FM) metal in cubic perovskite structure. By contrast, magnetic properties of epitaxial SrCoO$_{3}$ thin films, especially at high tensile strain ($\varepsilon \gtrsim 3$\%), remain unclear: Previous calculations had predicted antiferromagnetic (AFM) states more energetically favorable in this regime, but recent experiments indicated a FM insulating state. In this work, using first-principles calculations, we perform an extensive search for the structural, spin, magnetic, and orbital states of SrCoO$_{3}$ thin films. Our calculations ind…
Orbital mixing and strong Hund's coupling stabilize spin order in van der Waals ferromagnet CrI3
Technische Universität Berlin（柏林工业大学）；Fritz Haber Institute of the Max Planck Society（马克斯·普朗克学会弗里茨·哈伯研究所）；Vinča Institute of Nuclear Sciences - National Institute of the Republic of Serbia, University of Belgrade（贝尔格莱德大学文查核科学研究所）；ESRF, The European Synchrotron（欧洲同步辐射装置）；Politecnico di Milano（米兰理工大学）；Consiglio Nazionale delle Ricerche CNR-IOM, Unità di Trieste（国家研究委员会CNR-IOM的里雅斯特分部）；University of Milan-Bicocca（米兰比可卡大学）；Consiglio Nazionale delle Ricerche CNR-SPIN, c/o Università degli Studi ‘G. D’Annunzio’（国家研究委员会CNR-SPIN，挂靠阿布鲁佐大学）
The intrinsically hole-doped RbEuFe$_4$As$_4$ exhibits bulk superconductivity at $T_{\mathrm{sc}}=36.5$ K and ferromagnetic ordering in the Eu sublattice at $T_\mathrm{m}=15$ K. Here we present a hole-compensation study by introducing extra itinerant electrons via a Ni substitution in the ferromagnetic superconductor RbEuFe$_4$As$_4$ with $T_{\mathrm{sc}}>T_{\mathrm{m}}$. With the Ni doping, $T_{\mathrm{sc}}$ decreases rapidly, and the Eu-spin ferromagnetism and its $T_{\mathrm{m}}$ remain unchanged. Consequently, the system RbEu(Fe$_{1-x}$Ni$_x$)$_4$As$_4$ transforms into a superconducting fe…
