Magnetization relaxation in (Ga,Mn)As ferromagnetic semiconductors

TL;DR

This paper develops a theory for magnetization relaxation in (Ga,Mn)As semiconductors, linking microscopic interactions to damping behavior and implications for spintronic device switching currents.

Contribution

It introduces a theoretical model for Gilbert damping in (Ga,Mn)As based on p-d exchange coupling, connecting microscopic parameters with experimental data and device applications.

Findings

p-d coupling significantly affects damping in metallic samples

Theoretical Gilbert coefficient matches experimental ferromagnetic resonance data

Estimated critical current for spin-transfer switching is around 10^5 A/cm^2

Abstract

We describe a theory of Mn local-moment magnetization relaxation due to p-d kinetic-exchange coupling with the itinerant-spin subsystem in the ferromagnetic semiconductor (Ga,Mn)As alloy. The theoretical Gilbert damping coefficient implied by this mechanism is calculated as a function of Mn moment density, hole concentration, and quasiparticle lifetime. Comparison with experimental ferromagnetic resonance data suggests that in annealed strongly metallic samples, p-d coupling contributes significantly to the damping rate of the magnetization precession at low temperatures. By combining the theoretical Gilbert coefficient with the values of the magnetic anisotropy energy, we estimate that the typical critical current for spin-transfer magnetization switching in all-semiconductor trilayer devices can be as low as $\sim 10^{5} {\rm A cm}^{-2}$.