Spin and spin current—From fundamentals to recent progress

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.

Enhanced spin current transmissivity in Pt/ CoFe2O4 bilayers with thermally induced interfacial magnetic modification

“…The large enhancement in the θ 2 SH g ↑↓ eff produced by the thermally induced interfacial magnetic modification in CFO/Pt bilayers revealed by the SMR measurements must also be noticed in other phenomena relying on the spin-to-charge conversion process, such as the SSE. It consists in the generation of a spin current by a temperature gradient across a layer of a magnetic insulator that is detected by the voltage created along an attached metallic layer due to its conversion into a charge current [55][56][57][58][59][60][61][62]. The SSE has been widely studied in FMI/NM bilayers [55][56][57][58][59][60][61][62] and also in bilayers made of an antiferromagnetic material in contact with a nonmagnetic metallic film [63][64][65][66][67][68][69].…”

“…It consists in the generation of a spin current by a temperature gradient across a layer of a magnetic insulator that is detected by the voltage created along an attached metallic layer due to its conversion into a charge current [55][56][57][58][59][60][61][62]. The SSE has been widely studied in FMI/NM bilayers [55][56][57][58][59][60][61][62] and also in bilayers made of an antiferromagnetic material in contact with a nonmagnetic metallic film [63][64][65][66][67][68][69]. To confirm the SMR results discussed in the last section, we perform SSE experiments with the same two CFO/Pt samples.…”

Probing the Spin-Momentum Locking on Rashba Surfaces via Spin Current

“…These currents can be used to transport information and to exert torques on magnetic materials, as well as converting the spin current into a charge current and vice versa. 4 One prominent mechanism used to describe the spin-tocharge conversion in bulk materials is the direct and inverse spin Hall effect. 5 The direct spin Hall effect (SHE) is a phenomenon where an applied electric field induces the generation of a perpendicular pure spin current to its direction.…”

“…Unlike traditional electronics, which relies solely on the charge of electrons, spintronics harnesses both the charge and spin of electrons, providing a new pathway for creating more efficient and versatile electronic devices. − At the core of spintronics lies the fundamental concept of spin currents: currents that represent the flow of spin angular momentum. These currents can be used to transport information and to exert torques on magnetic materials, as well as converting the spin current into a charge current and vice versa …”

Actuation performance of a microstructure with spin-current volume effect

“…Recent progress in spintronics has led to the detection of various spin-mechanical interactions, but most of them are related to feeble forces [13][14][15][16][17][18]. Recently, there have been reports of magnetic material driven by spin-currents [19].…”