Domain wall motion induced by the magnonic spin current

Abstract

The spin-wave induced domain wall motion in a nanostrip with perpendicular magnetic anisotropy is studied. It is found that the domain wall can move either in the same direction or in the opposite direction to that of spin-wave propagation depending on whether the spin wave is reflected by the wall or transmitted through the wall. A magnonic momentum transfer mechanism is proposed and, together with the magnonic spin-transfer torque, a one-dimensional phenomenal model is constructed. The wall motion calculated based on this model is in qualitative agreement with micromagnetic simulations, showing that the model can describe the characteristics of spin-wave-induced wall motion and, especially, the wall motion direction.The magnetic domain wall motion induced by spin-transfer torque (STT) from a spin-polarized electrical current has attracted growing interest because of its fundamental relevance and potential applications in spintronic devices such as Racetrack memory and logic devices. 1-3 It is widely recognized that there are two types of STT acting on the wall when a spin-polarized current flows through it, namely the adiabatic STT and nonadiabatic STT. 4,5 The adiabatic STT comes from the adiabatic reversal of conduction electron spins, which induces a reaction torque on the wall as required by the conservation of angular momentum. 6 However, the origin of nonadiabatic STT still remains controversial. There are many contributions to this torque, such as spin-orbit interactions, spin-flip scattering, etc. 7-9 When the domain wall is narrow, the momentum transfer due to the electron reflection by the wall also contributes to the nonadiabatic STT. 10 The influence of the adiabatic and nonadiabatic STT on the wall motion is different. The adiabatic STT plays a more important role at the initial motion of the wall. It provides an initial velocity and causes the wall to move, but finally, it is balanced by an internal restoring torque and the wall motion ceases. 6 In contrast, the nonadiabatic STT behaves like a magnetic field and can sustain a steady-state wall motion. 5 Recently, the noncharge-based spin current, magnonic spin current, is proposed 11 and experimentally demonstrated. 12 Similar to the spin-polarized electrical current, the magnonic spin current also leads to the STT in the magnet and can be exploited to control the spin structures, including the displacement of the domain wall. Hinzke et al. 13 first demonstrated theoretically that a single domain wall in a nanowire can be displaced by a magnonic spin current due to the temperature gradient. Yan et al. 14 showed that a spin wave excited by a microwave field can also drive a wall motion. They suggested that the mechanism of wall motion is the spin transfer torque resulting from the angular momentum transfer between the magnons and the local magnetization in the wall. As a magnon moves across the wall, its angular moment is changed by 2h which is absorbed by the wall, making the wall propagate in the opposite direction to that of the magnon. It is wo...

Magnonic momentum transfer force on domain walls confined in space

“…However, the contrary was found in literature [13][14][15][16]: magnons push DWs to move along with them. The counteraction force due to linear MT between magnons and DWs could be a possible explanation for this phenomenon.…”

“…Due to the fact that the magnon excitation spectrum of the DW is different from that of a single domain, magnons incident on the DW get reflected, with a frequency-sensitive coefficient of reflection. As magnons are reflected back, a counteraction force is exerted on the DW and can be used to initiate DWM [13].In the presence of pure magnonic STT, DWs will move opposite to the propagation direction of the incident spin wave (SW) [10]. However, the contrary was found in literature [13][14][15][16]: magnons push DWs to move along with them.…”

“…Kim et al [16] employed a similar argument to shed light on the observed drag of DW by magnons in micromagnetic simulation. Wang et al [13] included the counteraction force phenomenologically in a 1D model to understand micromagnetic simulation results, and found qualitative agreement between model and simulation. The purpose of the current Letter is to show analytically in one dimension that the MT from the reflected magnons to a DW can actually exert a force on the DW, hence affecting p-1 the DW's motion.…”

“…As magnons are reflected back, a counteraction force is exerted on the DW and can be used to initiate DWM [13].…”

“…Due to the fact that the magnon excitation spectrum of the DW is different from that of a single domain, magnons incident on the DW get reflected, with a frequency-sensitive coefficient of reflection. As magnons are reflected back, a counteraction force is exerted on the DW and can be used to initiate DWM [13].…”