Simple theory for spin-lattice relaxation in metallic rare earth ferromagnets

TL;DR

This paper develops a theoretical model for spin-lattice relaxation times in metallic rare earth ferromagnets, specifically Gd, linking relaxation to spin-orbit effects and matching experimental data.

Contribution

It extends existing theories to calculate spin-lattice relaxation times in ferromagnetic rare earths, providing a quantitative estimate for Gd.

Findings

Calculated τ_SL for Gd as 48 ps

Good agreement with experimental measurements

Identified spin-orbit induced anisotropy as key factor

Abstract

The spin-lattice relaxation time $\tau_{SL}$ is a key quantity both for the dynamical response of ferromagnets excited by laser pulses and as the speed limit of magneto-optical recording. Extending the theory for the electron paramagnetic resonance of magnetic impurities to spin-lattice relaxation in ferromagnetic rare earths we calculate $\tau_{SL}$ for Gd and find a value of 48 ps in very good agreement with time-resolved spin-polarized photoemission experiments. We argue that the time scale for $\tau_{SL}$ in metals is essentially given by the spin-orbit induced magnetocrystalline anisotropy energy.