Anisotropic magnetic dynamics in (Ga, Mn)As film*

(Ga,Mn)As shows excellent magnetic properties which are usually described by a single-domain model. In this study, we perform a systematic investigation of ac magnetic susceptibility in (Ga,Mn)As films as a function of temperature and field carried out in parallel with dc magnetization measurements. A single ac susceptibility peak is observed close to T$_{C}$ for the field along [1-10] orientation; a single peak is seen close to 22 K along [110]; and both peaks are observed along [100]. Detailed analysis indicates that the peak near T$_{C}$ is related to the para-ferromagnetic transition. And the ferromagnetic domains nucleate with their easy axis aligned with [1-10] direction, involving 180$^{\circ}$ magnetization flips along the easy axis. The peak near 22 K, on the other hand, originates from magnetization switching between two biaxial easy axes separated by a small angle, which is induced by the competition between uniaxial and cubic anisotropy. Dynamic properties emerging from the distinct frequency dependences of the ac susceptibility in these two temperature regions, such as magnetic relaxation times, have been analyzed using various models. Investigations in patterned films will be carried out as well.