| アブストラクト: |
The photoinduced magnetism in hole-mediated ferromagnetic semiconductors have given us the opportunities to study spin manipulation by light, incorporating spin dynamics and non-linear effects for developing the future spin devices. Magnetization rotation has been demonstrated without an external magnetic field in (Ga,Mn), by controlling the hole spins though the chirality of light polarization and the p-d exchange interaction [1,2]. Successively, the studies on the dynamics of photoinduced magnetization rotation have been performed by measuring the time-resolved polar Kerr rotation. Surprisingly the magnetization rotation takes place instantaneously at the optical excitation. This inferrs us the possibility to realize the ultra-fast magnetization reversal beyond the classical precessional rotation. The rotated Mn spins relax within about 100 ps. On the other hand, in the time domain longer than 100 ps, a precession of Mn spins was observed. This precession is initiated by an increase in hole concentration, which results in the change in magnetic anisotropy. Consequently the effective magnetic field due to the change in magnetic anisotropy causes torque on Mn spins. This is first demonstration of photoinduced magnetization precession driven by photo-generated carriers.
[1] A. Oiwa et al., Phys. Rev. Lett. 88, 137202 (2002).
[2] Y. Mitsumori et al., Phys. Rev. B 69, 033203 (2004). |
