Magnonic momentum transfer force on domain walls confined in space

Abstract

PACS 75.30.Ds -Spin waves PACS 75.60.Ch -Domain walls and domain structure Abstract -Momentum transfer from incoming magnons to a Bloch domain wall is calculated using one dimensional continuum micromagnetic analysis. Due to the confinement of the wall in space, the dispersion relation of magnons is different from that of a single domain. This mismatch of dispersion relations can result in reflection of magnons upon incidence on the domain wall, whose direct consequence is a transfer of momentum between magnons and the domain wall. The corresponding counteraction force exerted on the wall can be used for the control of domain wall motion through magnonic linear momentum transfer, in analogy with the spin transfer torque induced by magnonic angular momentum transfer.Ever since its first proposal, manipulation of domain wall motion (DWM) using means other than the conventional magnetic field becomes one focus of the current research in nanomagnetism. The stimulus behind such intense investigation to find new ways for control of DWM is obvious, given the potential application of magnetic domain walls (DWs) as logic elements [1] and information storage bits [2]. Hydromagnetic drag [3], spin transfer torque (STT) [4,5] and momentum transfer (MT) force [6] due to the flow of electrons in metallic materials were proposed, and STT driven DWM was already demonstrated experimentally [7,8]. In contrast, using another important elementary excitation, magnons, to affect the motion of DW comes into horizon only recently. Magnon mediated electric current drag in a normal metal/ferromagnetic insulator/normal metal structure was studied by considering the interplay between electrical current and magnon current [9]. Magnonic STT was demonstrated, employing micromagnetic simulation and analytical calculation [10]. The main difference, or advantage, of magnonic STT compared to the conventional electronic STT lies on the fact that it is mediated by the flow of magnons, rather than electrons. Hence, in contrast to conventional STT whose operation requires the use of ferromagnetic metals, magnonic STT can work in ferromagnetic insulators, ame-(a) E-mail: dwwang@nudt.edu.cn (b) E-mail: guogh@mail.csu.edu.cn liorating significantly the Joule heating problem in metals. However, the MT due to the reflection of magnons by a DW is rarely discussed, simply because magnons travel in an infinitely-extended one-dimensional (1D) wall without any reflection [10][11][12]. The only effect of the presence of a DW is a wave-number dependent phase shift. For a 1D DW confined in space, the situation is different. 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 interactions between spin wave and stacked domain walls

“…Satisfyingly, here we find excellent agreement between v( f ) and SW reflection caused by STWs (Note that the reflection plot demonstrates relevant changes of the resonant peaks). This finding thus supports the mechanism of LMTT [9][10][11]18] and suggests that LMTT may apply to complex magnetic textures. On the other hand, the changes in v( f ) and SW reflection indicate that STWs cannot be viewed as a simple multiplication of the TWs.…”

“…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].…”

Magnonic band structure of domain wall magnonic crystals

“…Since a detailed derivation of the magnetization profile for a confined DW and the corresponding SW eigenfunction is given in Ref. [18], we will only describe the outline here. For brevity, in the following discussion of the DW magnetization profile and SW eigenfunction, the origin of the coordinate will be temporarily shifted to y = d 2 /4.…”

Equations of motion and frequency dependence of magnon-induced domain wall motion

“…1,2 On the other hand, conservation of linear momentum causes a domain wall to propagate away from the spin-wave source. 3,4 So far, experimental investigations of magnon-induced domain wall motion have mainly focused on dynamics induced by thermal magnons. 14,15 However, a domain wall in a temperature gradient can experience additional torques besides the purely magnonic ones, for instance the exchange stiffness can vary with temperature.…”

“…In such a scheme, global conservation laws determine the resulting domain wall velocity. [1][2][3][4] However, understanding dynamic phenomena such as a Walker breakdown requires knowledge about the dynamics of the collective coordinates that represent the domain wall. 23 Spin-wave-induced domain wall motion is a result of the back-action of the spin waves on the magnetic texture.…”