Abstract
High-resolution tunneling electron spin transport properties (longitudinal spin current (LSC) and spin transfer torque (STT) maps) of topologically distinct real-space magnetic skyrmionic textures are reported by employing a 3D-WKB combined scalar charge and vector spin transport theory in the framework of spin-polarized scanning tunneling microscopy (SP-STM). For our theoretical investigation metastable skyrmionic spin structures with various topological charges (Q=-3,-2,-1,0,1,2) in the (Pt0.95Ir0.05)/Fe/Pd(111) ultrathin magnetic film are considered. Using an out-of-plane magnetized SP-STM tip it is found that the maps of the LSC vectors acting on the spins of the magnetic textures and all STT vector components exhibit the same topology as the skyrmionic objects. In contrast, an in-plane magnetized tip generally does not result in spin transport vector maps that are topologically equivalent to the underlying spin structure, except for the LSC vectors acting on the spins of the skyrmionic textures at a specific relation between the spin polarizations of the sample and the tip. The magnitudes of the spin transport vector quantities exhibit close relations to charge current SP-STM images irrespectively of the skyrmionic topologies. Moreover, we find that the STT efficiency (torque/current ratio) acting on the spins of the skyrmions can reach large values up to ~25 meV/μA (~0.97 h/e) above the rim of the magnetic objects, but it considerably varies between large and small values depending on the lateral position of the SP-STM tip above the topological spin textures. A simple expression for the STT efficiency is introduced to explain its variation. Our calculated spin transport vectors can be used for the investigation of spin-polarized tunneling-current-induced spin dynamics of topologically distinct surface magnetic skyrmionic textures.
Highlights
Individual magnetic skyrmions are promising building blocks for high-density information storage and low-power information carrier applications in spintronics [1,2,3,4,5,6,7] due to their small size and topological properties
Employing a combined electron charge and vector spin transport theory within spin-polarized scanning tunneling microscopy (SP-STM), the high-resolution tunneling electron spin transport properties of a set of topologically distinct magnetic skyrmionic textures were investigated on a surface of a 2D hexagonal lattice
We reported important insights into their spin transport properties and their topological relation to the spin textures by providing 2D maps of longitudinal spin current (LSC) and spin transfer torque (STT) magnitudes and vector quantities in high spatial resolution obtained by differently magnetized scanning tips
Summary
Individual magnetic skyrmions are promising building blocks for high-density information storage and low-power information carrier applications in spintronics [1,2,3,4,5,6,7] due to their small size and topological properties. Controlled creation and annihilation of skyrmions have been reported in the seminal work of Romming et al [56] using local current pulses of the tip of an STM with opposite voltage polarities These effects have been explained by the electric fields in the STM junction [57], and very recently the transition rate was mapped on the nanometer scale [58], but the roles of the tunneling spin transfer torque (STT) and other spin transport processes in an SP-STM are less understood, and only a few works addressed such questions so far [59,60,61,62].
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