Topological Spintronics in Confined Geometry

One main objective of spintronics is to process and store information with the magnetic order parameters. Much of the recent attention is attracted by the magnetic skyrmions residing in magnetic materials with the antisymmetric Dzyaloshinskii-Moriya interaction. Here, we study skyrmion dynamics in two different confined geometries. We first demonstrate that single skyrmion creation and annihilation by spin waves in a crossbar geometry. A critical spin-wave frequency is required both for the creation and the annihilation of a skyrmion. The minimum frequencies for creation and annihilation are similar, but the optimum frequency for creation is below the critical frequency for skyrmion annihilation. Then we investigate the resonant modes of a single N\'eel type skyrmion in confined nanodisks with varying aspect ratios (AR). With the increase of disk AR, multiple new modes emerge in the power spectrum, which originate from the broken rotational symmetry of both the nanodisk and the skyrmion. Another goal of spintronics is to transport spin with minimal losses. Spin superfluid transport can be achieved in easy-plane ferromagnets and antiferromagnets by creating a non-equilibrium meta-stable state with static spin spiral textures. We show that the spin superfluid analogy can be extended to include Josephson-like oscillations of the spin current in both easy-plane ferromagnets and antiferromagnets. This spin current also has a non-linear, time-averaged component which provides a `smoking gun' signature of spin superfluidity. Furthermore, a spin oscillator device based on the spin superfluid Josephson effect is proposed