Spin drift velocity, polarization, and current-driven domain-wall motion in (Ga,Mn)(As,P)

Current-driven domain-wall motion is studied in (Ga,Mn)(As,P) ferromagnetic semiconducting tracks with perpendicular anisotropy. A linear steady state flow regime is observed over a large temperature range of the ferromagnetic phase (0.1T(c)相似文献   

Spin torque on magnetic domain walls exerted by supercurrents

We calculate the spin density, spin currents and spin torque due to a spin polarized current on a magnetic domain wall juxtaposed to or inserted in a conventional superconductor. The superconductor is part of a heterostructure of the type NSN or FSF. In general, the spin torque exerted on the domain wall is weaker with respect to a normal metal. However, there are regimes where the torque is enhanced with respect to the normal metal. In these regimes the motion of the domain wall is therefore more efficient. A notable case is the passing of an unpolarized current which leads to a finite torque in the case of the superconductor.     

Influence of current on field-driven domain wall motion in permalloy nanowires from time resolved measurements of anisotropic magnetoresistance

The motion of magnetic domain walls in permalloy nanowires is investigated by real-time resistance measurements. The domain wall velocity is measured as a function of the magnetic field in the presence of a current flowing through the nanowire. We show that the current can significantly increase or decrease the domain wall velocity, depending on its direction. These results are understood within a one-dimensional model of the domain wall dynamics which includes the spin transfer torque.     

Current-induced domain wall motion in magnetic nanowires with spatial variation

We model current-induced domain wall motion in magnetic nanowires with the variable width. Employing the collective coordinate method we trace the wall dynamics. The effect of the width modulation is implemented by spatial dependence of an effective magnetic field. The wall destination in the potential energy landscape due to the magnetic anisotropy and the spatial nonuniformity is obtained as a function of the current density. For a nanowire of a periodically modulated width, we identify three (pinned, nonlinear, and linear) current density regimes for current-induced wall motion. The threshold current densities depend on the pulse duration as well as the magnitude of wire modulation. In the nonlinear regime, application of ns order current pulses results in wall displacement which opposes or exceeds the prediction of the spin transfer mechanism. The finding explains stochastic nature of the domain wall displacement observed in recent experiments.     

Stability of the one-dimensional precession regime of a domain wall under a dc magnetic field in a uniaxial ferromagnet

The conditions for parametric excitation of flexural vibrations of a domain wall (DW) are determined in the case where the DW moves under the action of a uniform dc magnetic field whose strength exceeds the Walker critical value (in the spin precession regime). Vibrations are excited when uniform precession caused by the magnetic field during DW translational motion breaks down. Using numerical methods, it is shown that steady-state large-amplitude vibrations can occur and that these vibrations significantly affect the average DW velocity     

Current driven domain wall velocities exceeding the spin angular momentum transfer rate in permalloy nanowires

The velocity of domain walls driven by current in zero magnetic field is measured in permalloy nanowires using real-time resistance measurements. The domain wall velocity increases with increasing current density, reaching a maximum velocity of approximately 110 m/s when the current density in the nanowire reaches approximately 1.5 x 10(8) A/cm(2). Such high current driven domain wall velocities exceed the estimated rate at which spin angular momentum is transferred to the domain wall from the flow of spin polarized conduction electrons, suggesting that other driving mechanisms, such as linear momentum transfer, need to be taken into account.     

Temperature dependence of the spin torque effect in current-induced domain wall motion

We present an experimental study of domain wall motion induced by current pulses as well as by conventional magnetic fields at temperatures between 2 and 300 K in a 110 nm wide and 34 nm thick Ni80Fe20 ring. We observe that, in contrast with field-induced domain wall motion, which is a thermally activated process, the critical current density for current-induced domain wall motion increases with increasing temperature, which implies a reduction of the spin torque efficiency. The effect of Joule heating due to the current pulses is measured and taken into account to obtain critical fields and current densities at constant sample temperatures. This allows for a comparison of our results with theory.     

Magnetic friction in Ising spin systems

A new contribution to friction is predicted to occur in systems with magnetic correlations: Tangential relative motion of two Ising spin systems pumps energy into the magnetic degrees of freedom. This leads to a friction force proportional to the area of contact. The velocity and temperature dependence of this force are investigated. Magnetic friction is strongest near the critical temperature, below which the spin systems order spontaneously. Antiferromagnetic coupling leads to stronger friction than ferromagnetic coupling with the same exchange constant. The basic dissipation mechanism is explained. A surprising effect is observed in the ferromagnetically ordered phase: The relative motion can act like a heat pump cooling the spins in the vicinity of the friction surface.     

Electric polarization of magnetic textures: New horizons of micromagnetism

A common scenario of magnetoelectric coupling in multiferroics is the electric polarization induced by spatially modulated spin structures. It is shown in this paper that the same mechanism works in magnetic dielectrics with inhomogeneous magnetization distribution: the domain walls and magnetic vortexes can be the sources of electric polarization. The electric field driven magnetic domain wall motion is observed in iron garnet films. The electric field induced nucleation of vortex state of magnetic nanodots is theoretically predicted and numerically simulated. From the practical point of view the electric field control of micromagnetic structures suggests a low-power approach for spintronics and magnonics.     

Effect of fluctuations on the forced motion and interactions of domain walls in one-dimensional magnetic systems

Forced motion of a domain wall in the presence of fluctuations of external magnetic field and those of the parameters of the magnetic medium is studied. Calculations for the models of magnetic systems described by the sine-Gordon and Landau-Lifshitz equations are presented. It is shown that the driven motion of domain walls is characterized by the time-independent velocity distribution function which is used to calculate various statistical characteristics of the domain wall. Analysis of the mean velocity of the steady motion of the domain wall leads to the conclusion that the presence of a fluctuating magnetic field results in an increase of the effective relaxation constant of the magnetic system. In case of the sine-Gordon model the mean radiation power accompanying the forced motion of the domain wall is calculated. Inelastic interactions of two domain walls of opposite polarities are described.     

Domain wall motion in nanowires

We investigated the motion of domain walls in ferromagnetic cylindrical nanowires by solving the Landau–Lifshitz–Gilbert equation numerically for a classical spin model in which energy contributions from exchange, crystalline anisotropy, dipole–dipole interactions, and a driving magnetic field are considered. Depending on the diameter, either transverse domain walls or vortex walls are found. A transverse domain wall is observed for diameters smaller than the exchange length of the given system. In this case, the system effectively behaves one dimensionally and the domain wall velocity agrees with the result of Slonczewski for one-dimensional walls. For larger diameters, a crossover to a vortex wall sets in which enhances the domain wall velocity drastically. For a vortex wall the domain wall velocity is described by the Walker formula.     

Micromagnetic analysis of current-driven DW dynamics along rough strips with high perpendicular anisotropy at room temperature

Domain-wall motion along thin ferromagnetic strips with high perpendicular magnetocrystalline anisotropy driven by spin-polarized currents is theoretically analyzed by means of full micromagnetic simulations and one-dimensional model, both including surface roughness and thermal effects. At finite temperature, the results show a current dependence of the domain wall velocity in good qualitative agreement with available experimental observations, depicting a low-current, low velocity creep regime, and a high-current, linear regime separated by a smeared depinning region. The analysis points out the relevance of both thermal fluctuations and surface roughness on the domain wall dynamics, and confirms that these effects are essential to get a better understanding on the origin, the role and the magnitude of the non-adiabaticity by direct comparison with experiments.     

Fast current-induced motion of a transverse domain wall induced by interfacial Dzyaloshinskii–Moriya interaction

Based on a theoretical study, we show that the interfacial Dzyaloshinskii–Moriya interaction results in very efficient current-induced manipulation of a transverse domain wall in magnetic nanowires. The efficient domain wall motion is caused by combined effects of the domain wall distortion induced by the interfacial Dzyaloshinskii–Moriya interaction and the damping-like spin–orbit spin transfer torque. We find that with reasonable parameters, the domain wall velocity reaches a few hundreds m/s at the current density of 10⁷ A/cm², which has never been achieved before. Our result will be beneficial for low-power operation of domain wall devices.     

Stress dependence of the domain wall dynamics in the adiabatic regime

In this work, we determine the domain wall velocity in the low field region and study the domain dynamics in as-cast and annealed bi-stable amorphous glass-covered Fe_77.5Si_7.5B₁₅ microwires. In particular, from the relation between the domain wall velocity and magnetic field in the adiabatic regime, the power-law critical exponent β, the critical field H₀ and the domain wall damping η were obtained. It has been verified that the main source of domain wall damping is the eddy current and spin relaxation, both with a strong relation with the magnetoelastic energy. This energy term is changed by the axial applied stress, which, by its time, modifies the damping mechanisms. It was also verified that the domain wall damping terms present different behavior at low (mainly eddy currents) and high applied stress (spin relaxation).     

The stochastic nature of the domain wall motion along high perpendicular anisotropy strips with surface roughness

The domain wall dynamics along thin ferromagnetic strips with high perpendicular magnetocrystalline anisotropy driven by either magnetic fields or spin-polarized currents is theoretically analyzed by means of full micromagnetic simulations and a one-dimensional model, including both surface roughness and thermal effects. At finite temperature, the results show a field dependence of the domain wall velocity in good qualitative agreement with available experimental measurements, indicating a low field, low velocity creep regime, and a high field, linear regime separated by a smeared depinning region. Similar behaviors were also observed under applied currents. In the low current creep regime the velocity-current characteristic does not depend significantly on the non-adiabaticity. At high currents, where the domain wall velocity becomes insensitive to surface pinning, the domain wall shows a precessional behavior even when the non-adiabatic parameter is equal to the Gilbert damping. These analyses confirm the relevance of both thermal fluctuations and surface roughness for the domain wall dynamics, and that complete micromagnetic modeling and one-dimensional studies taking into account these effects are required to interpret the experimental measurements in order to get a better understanding of the origin, the role and the magnitude of the non-adiabaticity.     

Spin-transfer torques in antiferromagnetic metals from first principles

In spite of the absence of a macroscopic magnetic moment, an antiferromagnet is spin-polarized on an atomic scale. The electric current passing through a conducting antiferromagnet is polarized as well, leading to spin-transfer torques when the order parameter is textured, such as in antiferromagnetic noncollinear spin valves and domain walls. We report a first principles study on the electronic transport properties of antiferromagnetic systems. The current-induced spin torques acting on the magnetic moments are comparable with those in conventional ferromagnetic materials, leading to measurable angular resistances and current-induced magnetization dynamics. In contrast to ferromagnets, spin torques in antiferromagnets are very nonlocal. The torques acting far away from the center of an antiferromagnetic domain wall should facilitate current-induced domain wall motion.     

Classical dependence of the domain wall velocity on the magnetic field in garnet ferrite films with orthorhombic magnetic anisotropy

The dependence of the domain wall velocity V on the acting magnetic field H is investigated for bismuth-containing single-crystal garnet ferrite films with orthorhombic magnetic anisotropy. It is shown that this dependence includes both the initial linear portion and a saturation portion and exhibits a complex behavior. This behavior is explained within the model of domain wall motion with spin wave radiation.     

Current-driven magnetization switching and domain wall motion in nanostructures—Survey of recent experiments

An overview of recent experimental studies and new routes in the field of current-driven magnetization dynamics in nanostructured materials is given. The review introduces the basic concepts (Landau–Lifshitz phenomenology, critical current, spin currents in relation to spin accumulation, adiabatic/non-adiabatic spin-torque) and describes the main results of recent experiments on current-driven magnetization reversal within vertical pillar-like nanostructures and current-driven domain wall motion within laterally confined specimens. While for the pillar systems a discussion is provided of how the introduction of layers with perpendicular magnetic anisotropy, tunnel barriers and exchange bias and(or) oxide layers can be used to reduce the critical current densities for current-induced switching, the role of perpendicular anisotropy, use of spin valve structures, diluted magnetic semiconductors and epitaxial materials to increase the domain wall velocities are reviewed in the case of current-driven domain wall movement within lateral systems.     

Roles of the magnetic field and electric current in thermally activated domain wall motion in a submicrometer magnetic strip with perpendicular magnetic anisotropy

We have experimentally studied micrometer-scale domain wall (DW) motion driven by a magnetic field and an electric current in a Co/Pt multilayer strip with perpendicular magnetic anisotropy. The thermal activation energy for DW motion, along with its scaling with the driving field and current, has been extracted directly from the temperature dependence of the DW velocity. The injection of DC current resulted in an enhancement of the DW velocity independent of the current polarity, but produced no measurable change in the activation energy barrier. Through this analysis, the observed current-induced DW velocity enhancement can be entirely and unambiguously attributed to Joule heating.