Spin and spin current -- From fundamentals to recent progress

TL;DR

This paper reviews recent advances in spin and spin current physics, highlighting phenomena like spin pumping, spin-heat interactions, and mechanical-spin coupling, emphasizing their fundamental and technological significance.

Contribution

It provides a comprehensive overview of recent progress in spin current phenomena, including new effects and perspectives on spin-angular momentum conversion mechanisms.

Findings

Progress in spintronic phenomena driven by spin-exchange coupling

Advances in spin Seebeck and Peltier effects involving heat and spin interactions

Insights into mechanical motion's influence on electron and nuclear spins

Abstract

Along with the progress of spin science and spintronics research, the flow of electron spins, (i.e. spin current), has attracted interest. New phenomena and electronic states were explained in succession using the concept of spin current. Moreover, as many of the conventionally known spintronics phenomena became well organized based on spin current, it has rapidly been recognized as an essential concept in a wide range of condensed matter physics. In this article, we focus on recent developments in the physics of spin, spin current, and their related phenomena, where the conversion between spin angular momentum and different forms of angular momentum plays an essential role. Starting with an introduction to spin current, we first discuss the recent progress in spintronic phenomena driven by spin-exchange coupling: spin pumping, topological Hall torque, and emergent inductor. We, then, extend our discussion to the interaction/interconversion of spins with heat, lattice vibrations, and charge current and address recent progress and perspectives on the spin Seebeck and Peltier effects. Next, we review the interaction between mechanical motion and electron/nuclear spins and argue the difference between the Barnett field and rotational Doppler effect. We show that the Barnett effect reveals the angular momentum compensation temperature, at which the net angular momentum is quenched in ferrimagnets.