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We theoretically study a ferrimagnetic domain-wall motion driven by a rotating magnetic field. We find that, depending on the magnitude and the frequency of the rotating field, the dynamics of a ferrimagnetic domain wall can be classified into two regimes. First, when the frequency is lower than a certain critical frequency set by the field magnitude, there is a stationary solution for the domain-wall dynamics, where a domain-wall in-plane magnetization rotates in-phase with the external field. The field-induced precession of the domain wall gives rise to the translational motion of the domain wall via the gyrotropic coupling between the domain-wall angle and position. In this so-called phase-locking regime, a domain-wall velocity increases as the frequency increases. Second, when the frequency exceeds the critical frequency, a domain-wall angle precession is not synchronous with the applied field. In this phase-unlocking regime, a domain wall velocity decreases as the frequency increases. Moreover, the direction of the domain-wall motion is found to be reversed across the angular compensation point where the net spin density of the ferrimagnet changes its sign. Our work suggests that the dynamics of magnetic solitons under time-varying biases may serve as platform to study critical phenomena., Comment: 7 pages, 1 table, 3 figures

We theoretically investigate coupled gyration modes of magnetic solitons whose distances to the nearest neighbors are staggered. In a one-dimensional bipartite lattice, we analytically and numerically find that there is a midgap gyration mode bounded at the domain wall connecting topologically distinct two phases which is analogous to the Su-Schrieffer-Heeger model. As a technological application, we show that a one-dimensional domain-wall string in a two-dimensional soliton lattice can serve as a waveguide of magnetic excitations, which offers functionalities of a signal localization and selective propagation of the frequency modes. Our result offers an alternative way to control the magnetic excitation modes by using a magnetic metamaterial for future spintronic devices.

Exploiting spin transport increases the functionality of electronic devices and enables such devices to overcome physical limitations related to speed and power. Utilizing the Rashba effect at the interface of heterostructures provides promising opportunities toward the development of high-performance devices because it enables electrical control of the spin information. Herein, the focus is mainly on progress related to the two most compelling devices that exploit the Rashba effect: spin transistors and spin-orbit torque devices. For spin field-effect transistors, the gate-voltage manipulation of the Rashba effect and subsequent control of the spin precession are discussed, including for all-electric spin field-effect transistors. For spin-orbit torque devices, recent theories and experiments on interface-generated spin current are discussed. The future directions of manipulating the Rashba effect to realize fully integrated spin logic and memory devices are also discussed.

Topological protection precludes a continuous deformation between topologically inequivalent configurations in a continuum. Motivated by this concept, magnetic skyrmions, topologically nontrivial spin textures, are expected to exhibit topological stability, thereby offering a prospect as a nanometer-scale nonvolatile information carrier. In real materials, however, atomic spins are configured as not continuous but discrete distributions, which raises a fundamental question if the topological stability is indeed preserved for real magnetic skyrmions. Answering this question necessitates a direct comparison between topologically nontrivial and trivial spin textures, but the direct comparison in one sample under the same magnetic fields has been challenging. Here we report how to selectively achieve either a skyrmion state or a topologically trivial bubble state in a single specimen and thereby experimentally show how robust the skyrmion structure is in comparison with the bubbles. We demonstrate that topologically nontrivial magnetic skyrmions show longer lifetimes than trivial bubble structures, evidencing the topological stability in a real discrete system. Our work corroborates the physical importance of the topology in the magnetic materials, which has hitherto been suggested by mathematical arguments, providing an important step toward ever-dense and more-stable magnetic devices.

In optics, the Fabry–Perot interferometer is a basic building block, enabling a selection of light with a specific wavelength. We theoretically propose a magnonic version of the Fabry–Perot interferometer based on two magnetic domain walls. By exploiting the interaction of a domain wall and spin waves, in particular, the phenomenon that a sufficiently narrow domain wall serves as an effective mirror for spin waves as it reflects spin wave almost completely, a magnonic interferometer is contrived by using two parallel domain walls. It allows tunability of the magnon wavelength passing through the interferometer by changing the distance between two domain walls. Our result offers a way to improve the ability of magnonic information processing in a simple magnetic structure.

Magnetic domain wall motion is numerically studied in a nanowire with a Dzyaloshinskii-Moriya interaction (DMI) step at which DMI varies in real space. The spatially modulated DMI results in the formation of asymmetric domain wall energy landscape across the step, which affects the domain wall motion significantly. Utilizing this DMI step, we propose a domain wall memory device where the switching of up- and down-state is induced by a spin-orbit spin-transfer torque (SOT)-driven domain wall motion. This domain wall memory device is expected to have a high switching efficiency.

For a thin ferromagnetic film with the Dzyaloshinskii-Moriya interaction (DMI), we derive an expression of the extrinsic ferromagnetic resonance (FMR) linewidth in a quantum mechanical way, taking into account scatterings from structural inhomogeneity. In the presence of the DMI, the magnon dispersion exhibits rich resonant states, especially in small external magnetic fields and strong DMI strength. It is found that the FMR linewidth shows several characteristic features such as a finite linewidth at zero frequency and peaks in the low frequency range., 9 pages, 5 figures

Magnetic skyrmions are of considerable interest for low-power memory and logic devices because of high speed at low current and high stability due to topological protection. We propose a skyrmion field-effect transistor based on a gate-controlled Dzyaloshinskii-Moriya interaction. A key working principle of the proposed skyrmion field-effect transistor is a large transverse motion of skyrmion, caused by an effective equilibrium damping-like spin-orbit torque due to spatially inhomogeneous Dzyaloshinskii-Moriya interaction. This large transverse motion can be categorized as the skyrmion Hall effect, but has been unrecognized previously. The propose device is capable of multi-bit operation and Boolean functions, and thus is expected to serve as a low-power logic device based on the magnetic solitons., Comment: 16 pages, 3 figures