Dynamics of spin relaxation in nonequilibrium magnetic nanojunctions

TL;DR

This paper explores how spin relaxation behaves in magnetic nano-junctions under nonequilibrium conditions, revealing a maximum relaxation rate at intermediate coupling and effects of external voltage on damping.

Contribution

It introduces a combined classical and quantum numerical approach to study spin dynamics, highlighting non-monotonic relaxation rates and the impact of external voltages in magnetic nano-junctions.

Findings

Non-monotonic spin relaxation rates with a maximum at intermediate coupling

Resonant features in spin relaxation under external DC voltage

Accurate simulation of large systems using short chains with metallic leads

Abstract

We investigate nonequilibrium phenomena in magnetic nano-junctions using a numerical approach that combines classical spin dynamics with the hierarchical equations of motion technique for quantum dynamics of conduction electrons. Our focus lies on the spin dynamics, where we observe non-monotonic behavior in the spin relaxation rates as a function of the coupling strength between the localized spin and conduction electrons. Notably, we identify a distinct maximum at intermediate coupling strength, which we attribute to a competition that involves the increasing influence of the coupling between the classical spin and electrons, as well as the influence of decreasing local density of states at the Fermi level. Furthermore, we demonstrate that the spin dynamics of a large open system can be accurately simulated by a short chain coupled to semi-infinite metallic leads. In the case of a magnetic junction subjected to an external DC voltage, we observe resonant features in the spin relaxation, reflecting the electronic spectrum of the system. The precession of classical spin gives rise to additional side energies in the electronic spectrum, which in turn leads to a broadened range of enhanced damping in the voltage.