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...
The fundamental problem of domain wall (DW) inertia-the property that gives to inertial behaviors remains unclear in the physics of magnetic solitons. To understand its nature as well as to achieve accurate DW positioning and efficient manipulation of domain wall motion (DWM), spin wave (SW) pulse-induced DW transient effect is studied both numerically and theoretically in a magnetic nanostrip. It is shown for the first time that there occurs inevitable deceleration/automotion after SW pulse, which indicates nonzero DW inertia. The induced DWM is revealed to relate to two factors: energy storing within DW and out-of-plane tilting of DW. To explain the DWM dynamics, a one-dimensional collective model is developed to account for the excitation of spin wave pulse. The model successfully bridges DW energy, DW tilting and DW displacement and provides descriptions in accordance with numerical findings. It is made clear that the DW automotion hence DW inertia originate from the process of DW relaxation toward equilibrium. The DW inertia is expressed in terms of effective mass and turns out to be a time-dependent function with damping constant α as the governing parameter, which opposes the nature of intrinsic mass. For case containing multiple DWs, the total effective mass is shown to concern the reached velocity and stored energy of DWs instead of the number of DWs, which is against common intuition.
In this study, the interactions between spin wave (SW) and stacked domain walls in a magnetic nanostrip are investigated via micromagnetic simulation. It is found that under the excitation of SW, the metastable TWVW structure consisting of a transverse wall (TW) and a vortex wall (VW) may transform into a 360° wall or may completely annihilate depending on the frequency and amplitude of the SW. In contrast, stacked TWs (STWs) structure shows good robustness. Similar to a single TW, the STWs can be moved by SW and the inside TWs exhibit coherent motions. Notably, the frequency dependence of STWs’ velocity demonstrates obvious emergence, shift and disappearance of the resonant peaks. Such changes are found to be in accordance with SW reflection, which thus agrees with the mechanism of linear momentum transfer torque (LMTT). In concern with the SW transmission through STWs, we show that by varying TWs number and SW frequency, a wide range of transmission efficiency η can be obtained. At certain frequencies, η may increase with TWs number and may go beyond 100%, which indicates a lowered attenuation by STWs. On the other hand, the phase shift of the transmitted SW always increases linearly with the TWs number and can be resonantly enhanced at frequencies same as that of TWs normal modes. Mapping of SW reveals that the phase shift is a result of fast propagation of SW through TWs. The fast propagation and the low attenuation of SW through STWs suggests that STWs may serve as an excellent SW channel. Meanwhile, the induced STWs motion and the controlled SW transmission and phase shift by STWs also promises great uses of STWs in future magnonic devices and domain wall devices.
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