Quantum Theory of Spin-Transfer and Spin-Pumping in Collinear Antiferromagnets and Ferrimagnets

Abstract

Antiferromagnets are promising candidates as active components in spintronic applications. They share features with ferrimagnets in that opposing spin orientations exist in two or more sublattices. Spin transfer torque and spin pumping are essential ingredients in antiferromagnetic and ferrimagnet spintronics. This paper develops an out-of-equilibrium quantum theory of the spin dynamics of collinear magnets containing many spins coupled to normal metal reservoirs. At equilibrium, the spins are parallel or antiparallel to the easy axis. The theory, therefore, covers collinear antiferromagnets and ferrimagnets. We focus on the resulting semi-classical spin dynamics. The dissipation in the spin dynamics is enhanced due to spin-pumping. Spin accumulations in the normal metals induce deterministic spin-transfer torques on the magnet. Additionally, each electron's discrete spin angular momentum causes stochastic fluctuating torques on the antiferromagnet or ferrimagnet. We derive these fluctuating torques. The fluctuation-dissipation theorem holds at high temperatures, including the effects of spin-pumping. At low temperatures, we derive shot noise contributions to the fluctuations.

References in corpus (10)

• Spin pumping and spin-transfer torques in antiferromagnets
• Subterahertz spin pumping from an insulating antiferromagnet
• Spin transfer in an antiferromagnet
• Spin Insulatronics
• Functional Keldysh Theory of Spin Torques
• Spin pumping and shot noise in ferrimagnets: bridging ferro- and antiferromagnets
• Dynamic phase diagram of dc-pumped magnon condensates
• Spin-torque shot noise in magnetic tunnel junctions
• Absence of cross-sublattice spin pumping and spin-transfer torques in collinear antiferromagnets
• Quantum Scattering Theory of Spin Transfer Torque, Spin Pumping and Fluctuations