Chiral spin textures on the racetrack

Stuart Parkin, MPI Halle

The simplest chiral spin texture is a one-dimensional Néel magnetic domain wall that separates two magnetic regions that are magnetized in opposite directions. Under the influence of spin orbit torques, that are derived from spin currents that carry angular momentum, these walls can be driven at high speeds exceeding 1 km/sec along magnetic nano-wires that, thereby, form “magnetic racetracks”. This is the basic principle of the magnetic racetrack memory that stores digital data in the form of the presence or absence of such chiral domain walls. We discuss recent developments including the scaling of racetrack to sub-100 nm widths and the first 3D racetrack memory devices. Chiral domain walls are, however, just one member of an ever-expanding family of chiral spin textures that are of great interest from both a fundamental as well as a technological perspective. Recently a zoology of complex 2D and 3D spin textures stabilized by volume or interface Dzyaloshinskii-Moriya vector exchange interactions have been discovered including, in our work, anti-skyrmions, elliptical Bloch skyrmion, two-dimensional Néel skyrmions and fractional antiskyrmions. Such nano-objects are potential candidates as magnetic storage bits on the racetrack. Another class of chiral spin textures are Kagome antiferromagnets: we have recently shown how their complex spin textures can be manipulated by a previously unobserved seeded spin orbit torque (SSOT) mechanism. These chiral spin textures become superconducting when placed in proximity to a conventional superconductor and support long range triplet supercurrents. Triplet supercurrents are highly interesting in that they can carry spin angular momentum, unlike conventional superconductors, and, therefore, could be used, in principle, to manipulate chiral spin textures at ultra-low temperatures. This is the basic principle of the SUPERTRACK memory device that I have recently proposed [1].
[1] European Research Council Advanced Grant– SUPERMINT awarded to Stuart S.P. Parkin April, 2022.

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