Magnetization Reversal by Optical Spin Injection and its Memorization Effect in (Ga, Mn) as Thin Films

We have studied the effect of optical spin injection on the orientation of magnetization in ferromagnetic (Ga, Mn) As thin films. During the circularly polarized light illumination, the magnetization direction measured by anomalous Hall effect changes in either positive or negative direction depending on the light eliptcity. Magnitude of the change in magnetization reaches to 15 % of saturation magnetization at zero magnetic field despite the significantly small number of photogenerated carriers (holes) in the order of 10¹¹ cm^-3. When the light is removed, a part of the photoinduced change in magnetization is memorized. Since this memorization effect reflects the ferromagnetic behavior of sample well, rotation of ferromagnetic manganese may occur by spin polarized holes.