Spin Current

This chapter introduces the basic concept of spin current. It begins with an introduction to the general concept of spin and spin current, which is followed by a discussion of particular spin currents, such as incoherent, exchange, topological, and thermal spin currents. The chapter reviews the definition of charge currents for comparison. It talks about a diffusion spin current due to spatial inhomogeneous spin density and a drift spin current in the absence of coherent dynamics of spin. There are some methods for experimentally detecting pure spin currents, spin currents without accompanying charge currents. One direct method is the utilization of the inverse spin-Hall effect, a method which was demonstrated first by spin pumping and nonlocal technique. The chapter explains the exchange interaction in magnets by introducing a concept of an exchange spin current and then formulates a spin-wave spin current.