Magnetic properties and domain structure of (Ga,Mn)As films with perpendicular anisotropy

The ferromagnetism of a thin Ga(1-x)Mn(x)As layer with a perpendicular easy anisotropy axis is investigated by means of several techniques that yield a consistent set of data on the magnetic properties and the domain structure of this diluted ferromagnetic semiconductor. The magnetic layer was grown under tensile strain on a relaxed Ga(1-y)In(y)As buffer layer using a procedure that limits the density of threading dislocations. Magnetometry, magnetotransport, and polar magneto-optical Kerr effect (PMOKE) measurements reveal the high quality of this layer, in particular, through its high Curie temperature (130 K) and a well-defined magnetic anisotropy. We show that magnetization reversal is initiated from a limited number of nucleation centers and it develops by easy domain-wall propagation. Furthermore, MOKE microscopy allowed us to characterize in detail the magnetic domain structure. In particular, we show that the domain shape and wall motion are very sensitive to some defects, which prevents a periodic arrangement of the domains. We ascribed these defects to threading dislocations emerging in the magnetic layer, inherent to the growth mode on a relaxed buffer.