Energy equilibriation processes of electrons, magnons and phonons on the femtosecond timescale

TL;DR

This study investigates femtosecond energy dissipation processes among electrons, magnons, and phonons in magnetic materials using time-resolved Kerr spectroscopy, revealing limitations of existing microscopic models and effects of doping.

Contribution

It provides experimental insights into ultrafast energy relaxation in magnetic systems and challenges the predictions of Koopmans' microscopic model by showing doping-dependent relaxation behaviors.

Findings

Energy dissipation involves Elliot-Yafet scattering.

Doping affects nanosecond relaxation but not femtosecond processes.

Discrepancies suggest additional relaxation channels not in the model.

Abstract

By means of time-resolved Kerr spectroscopy experiments we relate the energy dissipation processes on the femtosecond (electron-spin relaxation time $\tau_{el-sp}$) and nanosecond timescale (Gilbert relaxation $\tau_{\alpha}$) and compare the results to the first microscopic model, which was proposed by Koopmans. For both energy dissipation processes, Elliot-Yafet scattering is proposed as the dominant contributor. We controllably manipulate the energy dissipation processes by transition metal doping (Pd) and rare earth doping (Dy) of a Permalloy film and find that while a change of $\tau_{\alpha}$ of more than a factor two is observed, \tau_{el-sp}$ remains constant, contrary to the predictions of the model. We explain the discrepancies by relaxation channels not considered in the original microscopic model and identify thereby the applicability of the model and possible necessary extensions to the model.