Thermal generation, manipulation and thermoelectric detection of skyrmions

Abstract

The magnetic skyrmion is a particle-like topologically stable spin texture that has been observed in chiral bulk magnets and asymmetric magnetic multilayers. Skyrmions can be generated and driven through the spin-polarized electric currents in the presence of an external magnetic field. Our early results show that the skyrmions can be thermally activated and behave like Brownian particles [1], which motivates us to explore the thermal control of skyrmion dynamics. Through using on-chip heaters, we are able to thermally generate, manipulate and thermoelectrically detect skyrmions [2]. Figure 1 shows that the skyrmion nucleation from the edge of the microstructured [Ta/CoFeB/MgO]15 multilayer, upon applying an electric current pulse to the upper heater on the side that generates local joule heating. The local creation of joule heating can facilitate a domain morphological transition and nucleate skyrmions by overcoming the low energy barrier. As the temperature of the heater is increased, more skyrmions are generated, which is accompanied by a unidirectional diffusion motion from the hot to the cold regions. This is due to the interplay among the repulsive forces between skyrmions, thermal spin-orbit torques, magnonic spin torques, and entropic forces. The ability to generate and manipulate skyrmions using heat opens another avenue of exploiting skyrmions in insulating and metallic materials. Moreover, by utilizing the anomalous Nernst effect in the same device, we can obtain the Nernst voltage which develops in the presence of a thermal gradient and magnetization perpendicular to each other. Since the magnetization can be varied by the change in the total number of skyrmions. We observed several discretized steps in the time evolution of Nernst voltages, as shown in Fig. 2. Each step is 90±10 nV which is attributed to the annihilation of a single skyrmion. The thermoelectric detection of skyrmion is important because the electrical detection of skyrmions is still challenging in many materials systems, but it is key to enabling spintronic applications. **