Search results for "Magnetism"
showing 10 items of 1934 documents
Theory of Current-Induced Angular Momentum Transfer Dynamics in Spin-Orbit Coupled Systems.
2020
Motivated by the importance of understanding competing mechanisms to current-induced spin-orbit torque in complex magnets, we develop a unified theory of current-induced spin-orbital coupled dynamics. The theory describes angular momentum transfer between different degrees of freedom in solids, e.g., the electron orbital and spin, the crystal lattice, and the magnetic order parameter. Based on the continuity equations for the spin and orbital angular momenta, we derive equations of motion that relate spin and orbital current fluxes and torques describing the transfer of angular momentum between different degrees of freedom. We then propose a classification scheme for the mechanisms of the c…
Magnon transport in the presence of antisymmetric exchange in a weak antiferromagnet
2021
The Dzyaloshinskii-Moriya interaction (DMI) is at the heart of many modern developments in the research field of spintronics. DMI is known to generate noncollinear magnetic textures, and can take two forms in antiferromagnets: homogeneous or inter-sublattice, leading to small, canted moments and inhomogeneous or intra-sublattice, leading to formation of chiral structures. In this work, we first determine the strength of the effective field created by the DMI, using SQUID based magnetometry and transport measurements, in thin films of the antiferromagnetic iron oxide hematite, $\alpha$-Fe$_2$O$_3$. We demonstrate that DMI additionally introduces reconfigurability in the long distance magnon …
Effect of magnons on the temperature dependence and anisotropy of spin-orbit torque
2020
We investigate the influence of magnons on the temperature-dependence and the anisotropy of the spin-orbit torque (SOT). For this purpose we use 3rd order perturbation theory in the framework of the Keldysh formalism in order to derive suitable equations to compute the magnonic SOT. We find several contributions to the magnonic SOT, which depend differently on the spin-wave stiffness $\mathcal{A}$ and on the temperature $T$, with the dominating contribution scaling like $T^{2}/\mathcal{A}^{2}$. Based on this formalism we compute the magnonic SOT in the ferromagnetic Rashba model. For large Rashba parameters the magnonic SOT is strongly anisotropic and for small quasiparticle broadening it m…
Spin-orbit torques from interfacial spin-orbit coupling for various interfaces
2017
We use a perturbative approach to study the effects of interfacial spin-orbit coupling in magnetic multilayers by treating the two-dimensional Rashba model in a fully three-dimensional description of electron transport near an interface. This formalism provides a compact analytic expression for current-induced spin-orbit torques in terms of unperturbed scattering coefficients, allowing computation of spin-orbit torques for various contexts, by simply substituting scattering coefficients into the formulas. It applies to calculations of spin-orbit torques for magnetic bilayers with bulk magnetism, those with interface magnetism, a normal metal/ferromagnetic insulator junction, and a topologic…
Large surface magnetization in noncentrosymmetric antiferromagnets
2020
Thin-film antiferromagnets (AFs) with Rashba spin-orbit coupling are theoretically investigated. We demonstrate that the relativistic Dzyaloshinskii-Moriya interaction (DMI) produces a large surface magnetization and a boundary-driven twist state in the antiferromagnetic N\' eel vector. We predict a magnetization on the order of $2.3\cdot 10^4$~A/m, which is comparable to the magnetization of ferromagnetic semiconductors. Importantly, the magnetization is characterized by ultra-fast terahertz dynamics and provides new approaches for efficiently probing and controlling the spin dynamics of AFs as well as detecting the antiferromagnetic DMI. Notably, the magnetization does not lead to any str…
Asymmetric skyrmion Hall effect in systems with a hybrid Dzyaloshinskii-Moriya interaction
2018
We examine the current-induced dynamics of a skyrmion that is subject to both structural and bulk inversion asymmetry. There arises a hybrid type of Dzyaloshinskii-Moriya interaction (DMI) which is in the form of a mixture of interfacial and bulk DMIs. Examples include crystals with symmetry classes C$_n$ as well as magnetic multilayers composed of a ferromagnet with a noncentrosymmetric crystal and a nonmagnet with strong spin-orbit coupling. As a striking result, we find that, in systems with a hybrid DMI, the spin-orbit-torque-induced skyrmion Hall angle is asymmetric for the two different skyrmion polarities ($\pm 1$ given by out-of-plane core magnetization), even allowing one of them t…
Concepts of antiferromagnetic spintronics
2017
Antiferromagnetic spintronics is an emerging research field whose focus is on the electrical and optical control of the antiferromagnetic order parameter and its utility in information technology devices. An example of recently discovered new concepts is the N\'{e}el spin-orbit torque which allows for the antiferromagnetic order parameter to be controlled by an electrical current in common microelectronic circuits. In this review we discuss the utility of antiferromagnets as active and supporting materials for spintronics, the interplay of antiferromagnetic spintronics with other modern research fields in condensed matter physics, and its utility in future "More than Moore" information tech…
Skyrmions and multi-sublattice helical states in a frustrated chiral magnet
2016
We investigate the existence and stability of skyrmions in a frustrated chiral ferromagnet by considering the competition between ferromagnetic (FM) nearest-neighbour (NN) interaction ($J_1$) and antiferromagnetic (AFM) next-nearest-neighbour (NNN) interaction ($J_2$). Contrary to the general wisdom that long-range ferromagnetic order is not energy preferable under frustration, the skyrmion lattice not only exists but is even stable for a large field range when $J_2 \leq J_1$ compared with frustration-free systems. We defend that the enlargement of stability window of skyrmions is a consequence of the reduced effective exchange interaction caused by the frustration. A multi-sublattice helic…
Comparison of first-principles methods to extract magnetic parameters in ultra-thin films: Co/Pt(111)
2019
We compare three distinct computational approaches based on first-principles calculations within density functional theory to explore the magnetic exchange and the Dzyaloshinskii-Moriya interactions (DMI) of a Co monolayer on Pt(111), namely, (i) the method of infinitesimal rotations of magnetic moments based on the Korringa-Kohn-Rostoker (KKR) Green function method, (ii) the generalized Bloch theorem applied to spiraling magnetic structures and (iii) supercell calculations with noncollinear magnetic moments, the latter two being based on the full-potential linearized augmented plane wave (FLAPW) method. In particular, we show that the magnetic interaction parameters entering micromagnetic …
Laser-induced torques in spin spirals
2020
We investigate laser-induced torques in magnetically non-collinear ferromagnets with a spin-spiral magnetic structure using \textit{ab-initio} calculations. Since spin-spirals may be used to approximate the magnetization gradients locally in domain walls and skyrmions, our method may be used to obtain the laser-induced torques in such objects from a multiscale approach. Employing the generalized Bloch-theorem we obtain the electronic structure computationally efficiently. We employ our method to assess the laser-induced torques in bcc Fe, hcp Co, and L$_{1}0$ FePt when a spin-spiral magnetic structure is imposed. We find that the laser-induced torques in these magnetically noncollinear syst…