Spin Dynamics in a Tunnel Junction between Ferromagnets

TL;DR

This paper investigates the complex spin dynamics in a tunnel junction between ferromagnets, revealing novel behaviors like nutation due to lead magnetization configurations using advanced quantum techniques.

Contribution

It introduces a quantum Langevin equation approach to describe spin dynamics in ferromagnetic tunnel junctions, highlighting effects of lead magnetization orientation.

Findings

Spin exhibits nutation when magnetizations are unequal or non-parallel.

Parallel magnetizations produce standard Larmor precession.

Predictions applicable to macroscopic spin clusters.

Abstract

The dynamics of a single spin embedded in the tunnel junction (quantum point contact) between ferromagnets is addressed. Using the Keldysh technique, we derive a quantum Langevin equation. As a consequence of the spin-polarization in the leads, the spin displays a rich and unusual dynamics. Parallel configured and equally strong magnetic moments in the leads yield an ordinary spin precession with a Larmor frequency given by the effective magnetic field. Unequal and/or non-parallel configured magnetization, however, causes nutation of the spin in addition to the precession. Our predictions may be directly tested for macroscopic spin clusters.