Non-thermal laser induced precession of magnetization in ferromagnetic semiconductor (Ga,Mn)As

TL;DR

This paper demonstrates non-thermal laser-induced magnetization precession in (Ga,Mn)As, revealing the role of angular momentum transfer from femtosecond laser pulses and controlling thermal effects via piezoelectric methods.

Contribution

It provides the first experimental evidence of non-thermal laser-induced magnetization dynamics in ferromagnetic semiconductors with systematic analysis and theoretical interpretation.

Findings

Coherent magnetization dynamics can be excited non-thermally in (Ga,Mn)As.

Thermal effects can be suppressed using piezoelectric control.

Angular momentum transfer from circularly polarized femtosecond laser pulses drives the precession.

Abstract

Non-thermal laser induced spin excitations, recently discovered in conventional oxide and metal ferromagnets, open unprecedented opportunities for research and applications of ultrafast optical manipulation of magnetic systems. Ferromagnetic semiconductors, and (Ga,Mn)As in particular, should represent ideal systems for exploring this new field. Remarkably, the presence of non-thermal effects has remained one of the outstanding unresolved problems in the research of ferromagnetic semiconductors to date. Here we demonstrate that coherent magnetization dynamics can be excited in (Ga,Mn)As non-thermally by a transfer of angular momentum from circularly polarized femtosecond laser pulses and by a combination of non-thermal and thermal effects due to a transfer of energy from laser pulses. The thermal effects can be completely suppressed in piezo-electrically controlled samples. Our work is based on pump-and-probe measurements in a large set of (Ga,Mn)As epilayers and on systematic analysis of circular and linear magneto-optical coefficients. We provide microscopic theoretical interpretation of the experimental results.