Tailoring elastic and inelastic collisions of relativistic antiferromagnetic domain walls.

Soliton-based computing relies on their unique properties for transporting energy and emerging intact from head-on collisions. Magnetic domain walls are often referred to as solitons disregarding the strict mathematical definition requiring the above scattering property. Here we demonstrate the conditions of elastic and inelastic scattering for spin-orbit torque-induced dynamics of relativistic domain walls on the technologically relevant Mn[Formula: see text]Au antiferromagnetic material.

Synthetic ferrimagnet nanowires with very low critical current density for coupled domain wall motion.

Domain walls in ferromagnetic nanowires are potential building-blocks of future technologies such as racetrack memories, in which data encoded in the domain walls are transported using spin-polarised currents. However, the development of energy-efficient devices has been hampered by the high current densities needed to initiate domain wall motion. We show here that a remarkable reduction in the critical current density can be achieved for in-plane magnetised coupled domain walls in CoFe/Ru/CoFe synthetic ferrimagnet tracks.

Dzyaloshinskii-Moriya Interaction as a Consequence of a Doppler Shift due to Spin-Orbit-Induced Intrinsic Spin Current.

We present a physical picture for the emergence of the Dzyaloshinskii-Moriya (DM) interaction based on the idea of the Doppler shift by an intrinsic spin current induced by spin-orbit interaction under broken inversion symmetry. The picture is confirmed by a rigorous effective Hamiltonian theory, which reveals that the DM coefficient is given by the magnitude of the intrinsic spin current. Our approach is directly applicable to first principles calculations and clarifies the relation between the interaction and the electronic band structures.

Controlling and probing non-abelian emergent gauge potentials in spinor Bose-Fermi mixtures.

Gauge fields, typified by the electromagnetic field, often appear as emergent phenomena due to geometrical properties of a curved Hilbert subspace, and provide a key mechanism for understanding such exotic phenomena as the anomalous and topological Hall effects. Non-abelian gauge potentials serve as a source of non-singular magnetic monopoles. Here we show that unlike conventional solid materials, the non-abelianness of emergent gauge potentials in spinor Bose-Fermi atomic mixtures can be continuously varied by changing the relative particle-number densities of bosons and fermions.

Thermal vector potential theory of transport induced by a temperature gradient.

A microscopic formalism to calculate thermal transport coefficients is presented based on a thermal vector potential, whose time derivative is related to a thermal force. The formalism is free from the unphysical divergences reported to arise when Luttinger's formalism is applied naively, because the equilibrium ("diamagnetic") currents are treated consistently. The mathematical structure for the thermal transport coefficients is shown to be identical with that for the electric ones if the electric charge is replaced by the energy.

Two-barrier stability that allows low-power operation in current-induced domain-wall motion.

Energy barriers in magnetization reversal dynamics have long been of interest because the barrier height determines the thermal stability of devices as well as the threshold force triggering their dynamics. Especially in memory and logic applications, there is a dilemma between the thermal stability of bit data and the operation power of devices, because larger energy barriers for higher thermal stability inevitably lead to larger magnetic fields (or currents) for operation. Here we show that this is not the case for current-induced magnetic domain-wall motion induced by adiabatic spin-transfer torque.

Ultrafast magnetic vortex core switching driven by the topological inverse Faraday effect.

We present a theoretical discovery of an unconventional mechanism of inverse Faraday effect which acts selectively on topological magnetic structures. The effect, topological inverse Faraday effect, is induced by the spin Berry's phase of the magnetic structure when a circularly polarized light is applied. Thus a spin-orbit interaction is not necessary unlike that in the conventional inverse Faraday effect.

Charge current driven by spin dynamics in disordered Rashba spin-orbit system.

Pumping of charge current by spin dynamics in the presence of the Rashba spin-orbit interaction is theoretically studied. Considering a disordered electron, the exchange coupling and spin-orbit interactions are treated perturbatively. It is found that the dominant current induced by spin dynamics is interpreted as a consequence of the conversion from spin current via the inverse spin Hall effect.

Microscopic theory of current-driven domain wall motion.

The dynamics of a domain wall in ferromagnetic nanowires under electric current is theoretically studied. The driving mechanism is shown to depend on wall thickness. Thick walls, as in metallic wires, are propelled by the spin torque arising from spin polarization of current, while thin walls, as in nanocontacts and magnetic semiconductors, are driven by the pressure from charge current.

Effect of spin current on uniform ferromagnetism: domain nucleation.

A large spin current applied to a uniform ferromagnet leads to a spin-wave instability as pointed out recently. In this Letter, it is shown that such spin-wave instability is absent in a state containing a domain wall, which indicates that nucleation of magnetic domains occurs above a certain critical spin current. This scenario is supported also by an explicit energy comparison of the two states under spin current.

Current-induced resonance and mass determination of a single magnetic domain wall.

A magnetic domain wall (DW) is a spatially localized change of magnetization configuration in a magnet. This topological object has been predicted to behave at low energy as a composite particle with finite mass. This particle will couple directly with electric currents as well as magnetic fields, and its manipulation using electric currents is of particular interest with regard to the development of high-density magnetic memories.

Theory of current-driven domain wall motion: spin transfer versus momentum transfer.

A self-contained theory of the domain wall dynamics in ferromagnets under finite electric current is presented. The current has two effects: one is momentum transfer, which is proportional to the charge current and wall resistivity (rho(w)); the other is spin transfer, proportional to spin current. For thick walls, as in metallic wires, the latter dominates and the threshold current for wall motion is determined by the hard-axis magnetic anisotropy, except for the case of very strong pinning.

Quantum toys for quantum computing: persistent currents controlled by the spin Josephson effect.

Quantum devices and computers will need operational units in different architectural configurations for their functioning. The unit should be a simple "quantum toy," an easy to handle superposition state. Here such a novel unit of quantum mechanical flux state (or persistent current) in a conducting ring with three ferromagnetic quantum dots is presented.