Spin dynamics in ferromagnetic p-(Ga,Mn)As (x = 0.011, TC = 30 K) has been studied by carefully comparing the decay time of the photo-induced reflectivity change with the transient behavior of polar Kerr rotation induced by photo-generated carrier spins with a femtosecond light pulse of various polarizations. As to the rising process, the rate of Kerr rotation is found comparable to the generation rate of spin-polarized carriers. For the decay process, the Kerr rotation and reflectivity signal both show the same decay rate at above the TC, whereas, below the TC, the former becomes slower than the latter. The magnitude of Kerr rotation suggests that 102 Mn spins are revolved by injecting one hole spin. On the basis of these observations, collective rotation of ferromagnetically coupled Mn spins is discussed in terms of p-d exchange interaction and successive transverse spin relaxation. Development of another long-lived behavior under external perpendicular magnetic fields is also disclosed.
@article{arxiv.cond-mat/0307268,
title = {Photo-induced spin dynamics in ferromagnetic semiconductor $p$-(Ga,Mn)As},
author = {Y. Mitsumori and A. Oiwa and T. Slupinski and H. Maruki and Y. Kashimura and F. Minami and H. Munekata},
journal= {arXiv preprint arXiv:cond-mat/0307268},
year = {2007}
}