Quantifying arbitrary-spin-wave-driven domain wall motion, the creep nature of domain wall and the mechanism for domain wall advances

Abstract

Domain wall motion (DWM) by spin waves (SWs) in different waveforms in a magnetic nanostripe is investigated via micromagnetic simulations. Diversified DWMs are observed. It is found that SW harmonic drives DWM most efficiently and irregular SW may cause abnormal excitation spectrum for DWM in the low-frequency range. We prove that SW harmonic is the basic element when interacting with DW and causes simple creeping motion of DW (i.e. forward propagation of DW accompanied with oscillation) with the same frequency as applied SW harmonic. Under irregular/polychromatic SW, DW makes responses to the energies carried by constituent SW harmonics, instead of overall exhibited torques, and simultaneously conducts multiple creeping motions. This finding enables the analysis for the induced DWM under arbitrary SW. Mapping of SW inside DW reveals that the simple creeping motion is due to real-space expansion and contraction inside DW and the monolithic translation of DW. It is further elucidated that the former relates to the transmitting of spin torques of SW through DW and the latter corresponds to the absorption of spin torques by DW. The overall absorbed spin torques point to direction same as SW propagation and drive DW forward. In addition, the absorption mechanism is evidenced by the well agreement between absorption of SW and averaged velocity of DW. various magnetic structures. In addition, the ability to assist other approaches for improved performance in DWM gives it an extra advantage [50,51].On the other hand, the interplay between SW and DW remains interesting in fundamental physics. Although great effort has been made in understanding the basic characteristics of SW-induced DWM in terms of both theoretical analysis [34,35,[37][38][39]41] and micromagnetic simulations [32-36, 40, 42], the precise picture in dynamics was never determined. So far, two major mechanisms were proposed: magnonic spin-transfer torque (STT) [34] and magnonic linear momentum transfer torque (LMTT) [11,35]. In STT (for a simplified 1D model), linearization on Landau-Lifshitz-Gilbert (LLG) equation gives a solution of reflectionless propagating SW described by a Schrodinger equation. The obtained SW carries a constant magnon current transmitting through DW. Magnons can be viewed as spin-1 bosons with angular momentum ±ÿ and linear momentum ÿk. As a magnon passes through the DW, its spin is changed by 2ÿ; according to the conservation of angular momentum, the spin of 2ÿ must be transferred to DW, which further results in the backward motion of DW with respect to SW propagation [34,41]. On the other hand, what concerns the LMTT theory is the conservation law for linear momentum. LMTT was proposed to explain cases with reflection. Reflected magnon reverses its wave vector k in sign. That is, the linear momentum is changed by 2ÿk. The transfer of linear momentum to DW rewrites the effective field in LLG and causes forward motion of DW [35,42]. STT and LMTT can only be partially correct due to the fact that SW transmission varies with frequenc...

Current driven properties and the associated magnetic domain walls manipulation in U-shaped magnetic nanowires

“…The [31] shows that the spin wave assistance can enhance the current driven magnetic domain wall movement, so it can be used to reduce driving current. In addition, the previous research has shown that spin wave driving the magnetic domain walls movement depends on its amplitude and frequency [32][33][34]. In detail, the speed of spin wave driven domain wall movement is linearly dependent on the amplitude of the spin wave, but nonlinearly dependent on the frequency of the spin wave.…”

The interactions between spin wave and stacked domain walls

“…To understand the origin of the forward shifting of SW phase, propagations of SW through a single head-to-head TW have been mapped [4,19], see figure 13. It is found that SW can propagate with larger velocity inside of TW (see the black solid lines) than in uniform magnetization (see the black dashed lines).…”

“…where M is the local magnetization vector, H eff is the effective field, γ = μ 0 eg 2m e is the gyromagnetic ratio, and α is the In order to model infinite length of the nanostip as well as to avoid possible distortion of the nanostripe, the left-end and right-end edges are artificially pinned [4]. Meanwhile, to prevent SW reflection from the two ends, each end within 100 × 40 × 5 nm 3 is assigned with increased α which varies linearly from 0.01 to 1 [17,55] such that the SW are sufficiently damped near edges.…”

“…Physics-wise, it has been shown that under arbitrary SW, DW makes responses to the energies carried by constitutional SW harmonics and the induced domain wall motion (DWM) can be understood in terms of Fourier analysis [4]. As SW travels through an ideal 1-D transverse wall (Bloch wall [5,6] or Neel wall [6,7]), no reflection arises and the transmitted SW carries a phase shift [5][6][7][8].…”

“…The backward DWM was ascribed to the transmitted SW and explained by the mechanism of magnonic spin-transfer torque (STT) [7,16]. In order to explain the forward DWM, SW absorption mechanism [4] and SW reflection-associated magnonic linear momentum transfer torque (LMTT) mechanism have been proposed [9][10][11]18]. In addition to the induced DWM, SW can also excite DW and cause out-of-plane tilting of DW, which further gives rise to DW automotion and DW effective mass [19].…”