Observation of Non-Collinear Magnetoresistance by Scanning Tunneling Spectroscopy on Skyrmions in PdFe/Ir(111)

Abstract

Magnetic skyrmions are non-collinear spin arrangements with an axial symmetry and a fixed rotational sense. This fixed rotational sense implies a topology leading to an elevated stability of skyrmions against external perturbations which qualifies skyrmions as potential candidates for the application in spintronic devices. In this work, the electronic structure of isolated magnetic skyrmions in PdFe/Ir(111) is investigated by means of non –spin-polarized scanning tunneling microscopy and spectroscopy, and the interaction of skyrmions with native in-layer defects, Co adatoms and Co clusters is studied. In the first part, the significant difference between the vacuum local density of states measured on a collinear (ferromagnetic) and a non-collinear magnetic environment (skyrmion center) is investigated. A new type of magnetoresistive effect called non-collinear magnetoresistance (NCMR) is described. This effect allows the detection of a complex non-collinear spin structure without the necessity of spin-polarized electrodes similar to a change by the tunneling anisotropic magnetoresistance effect, but much larger in magnitude. In the second part, a proof-of-principle type study on the interaction of skyrmions with in-layer defects, Co adatoms and Co clusters on top of the surface is performed. The controlled writing and deleting of individual skyrmions is demonstrated as well as the movement of an isolated skyrmion which is induced by moving a cluster with the tip of a scanning tunneling microscope. This study demonstrates a step towards an application of skyrmions in future devices.