[12p-M101-1~14] 10.4 Semiconductor spintronics, superconductor, multiferroics

▲ [12p-M101-2] Experimental evidence for non-thermal aspect of photo-excited precession of magnetization in (Ga,Mn)As

〇Hiro Munekata¹, Takashi Matsuda¹ (1.FIRST, Tokyo Tech)

Keywords:ferromagnetic semiconductors, fs-laser excitation, photo-induced angular momentum

Many laboratories has found that the photo-excited precession of magnetization in p-(Ga,Mn)As is triggered by femto-second laser pulses with relatively low laser fluence (< 10 micro-J per cm²) without either external fields or angular momentum of light, but the mechanism of perpendicular anisotropy dH remains open. We report the optical responses of various GaMnAs samples at two different time scales; the relatively long time scale (< 1ns) and ultra-short time scale (< 1 ps). In the long time-scale, dH is generated within 10 - 20 ps for below-gap excitation and ~ 100 ps for above-gap excitation. In the ultra-short time scale, coherent and nearly coherent autocorrelation between pump and probe beams via photo-generated carries have been observed. The LLB equation including ultrafast quenching has failed to reproduce the experimental positive spikes. With all these, we have addressed new mechanism for the photo-induced dH: photo-ionization-like excitation of Mn²⁺; namely, Mn²⁺ + hv --> Mn³⁺ + e^- with the dynamic concentration gradient along the z axis.