Domain wall motion and spin structure transformations in Permalloy nanowires induced by current and field

摘要: Domain walls (DWs) propagated along nanoscale magnetic wires by electrical current or field are a fascinating prospect for applications in magnetic logic and data storage [1]. However, to realize working devices, a thorough understanding of the underlying physics must be developed. For current-induced DW motion a key question concerns the relation between the magnetization damping α and the non-adiabaticity of the spin transport β. These parameters are predicted to control the nature of the DW motion including DW spin structure transformations [2]. Meanwhile for DWs propagated by field alone, according to the 1D model of Schryer and Walker [3] there is the possibility of tailoring the DW velocity by varying the damping.We investigate current-induced DW motion and transformations in 1500 nm-wide Permalloy (Ni80Fe20) wires of thickness 8-20 nm by means of X-ray magnetic circular dichroism photoemission electron microscopy (XMCD-PEEM). Depending on the wire thickness and current density, we observe periodic DW transformations, simple translation of vortex-type DWs and vortex nucleation and annihilation, as reported in [4, 5]. Selected results are shown in Figure 1. Altering the damping in the Permalloy by rare earth doping, we find that there is no significant change in the DW velocity. The results imply that the non-adiabaticity β does not equal the damping α, in agreement with theoretical predictions [6], and that the angular momentum dissipation that causes viscous damping and the spin relaxation that leads to nonadiabatic transport are intimately connected.