Magnetic structures have been studied extensively in the past decades, mostly concentrated in information storage, and information processing more recently. However, the exploration of the capability of magnetic structure beyond such information related applications is still lacking. Through collaboration with Prof. Yaroslav Tserkovnyak, we introduce a novel idea of using the topological nature of spin textures for energy storage, i.e. a spin battery. Different from the conventional chemical batteries, the spin battery does not degrade over time with infinite charging and discharging cycles. This proposal is published on Physical Review Letters as editor's suggestion (link).
The idea of storing energy using a topological spin texture can be illustrated by analogy with a twisted rod (pictured right), as proposed by Sonin in the context of a general supercurrent. The energy is loaded into the rod by applying opposite torques at the ends, and then stored as the mechanical twisting. To prevent the rod from untwisting, the two ends are fused together.
A magnetic rod can store energy in a similar manner, but by the means of magnetic rather than mechanical twisting. The process is more or less the same as the twisted rod, except that the winding is taking place in spin space, without any (mechanically) moving parts. We start with a free magnetic rod with a homogeneous spin texture, of which the magnetization is constrained in the easy plane normal to the rod axis. By applying opposite spin torques (via a spin current injection) to the magnetization at the ends, the magnetization starts to twist in the easy plane and forms a spin spiral. The energy is stored in the spiral in the form of a magnetic exchange. To keep the spirals from unwinding, the magnetizations at the ends have to be pinned or fused together. To release the stored magnetic energy, we open the spin-spiral ends, releasing the energy in the form of magnetization dynamics, which can be harvested electrically via a spin-motive force. A prototype spin battery is illustarted on the PRL webpage screenshot above with winding wires for spin injection and spin extraction, as well as a short segment for breaking and fusing the magnetic loop.
While at present, the spin battery appears challenging to compete with the traditional lithium-ion technology in terms of the energy density, our proposal already has a clear advantage specifically for spintronic circuits, where the topological spin-texture energy storage can be naturally integrated with the nonvolatile logic and memory functionalities.
This project is a collaboration with Prof. Yaroslav Tserkovnyak at UCLA. The idea was cooked up during Prof. Tserkovnyak’s visit to Fudan in the summer of 2017 before his trip to Spin Summit 2017. We brainstormed purposely on the application of using antiferromagnet for storing energy. Eventually, we ended up with this energy storage device via spin textures instead.