Dynamics of magnetization and carriers at the onset of the photo-excited precession of magnetization in (Ga,Mn)As

TL;DR

This study investigates the ultrafast magnetization dynamics in (Ga,Mn)As using time-resolved optical techniques, revealing that observed signals are due to carrier interference effects rather than demagnetization, with Mn ion photo-ionization influencing magnetic anisotropy.

Contribution

It introduces a new interpretation of ultrafast signals in (Ga,Mn)As, attributing them to carrier interference rather than demagnetization, and proposes Mn ion photo-ionization as a key mechanism.

Findings

Rapid oscillations and spike signals observed below and above GaAs band gap.

Signals are due to pump-probe interference, not ultrafast demagnetization.

Photo-ionization of Mn ions affects magnetic anisotropy.

Abstract

Photo-excited precession of magnetization in (Ga,Mn)As is investigated by measuring time-resolved magneto-optical response and transient differential reflectivity with pump-and-probe technique. In the time region less than 1 ps, rapidly oscillating and spike-like signals are observed, respectively, with excitation of below and above the GaAs band gap. Analysis with gyromagnetic model and autocorrelation function concludes that those signals are not attributed to ultrafast demagnetization but due to interference between pump and probe pulses incorporating sub-ps carrier dynamics characteristic of low-temperature grown semiconductors. Photo-ionization of Mn ions (Mn2+ -> Mn3+) is proposed as a mechanism which dynamically induces orbital angular momentum and affects hole-mediated magnetic anisotropy in (Ga,Mn)As.