Unusual domain-wall motion in ferromagnetic semiconductor films with tetragonal anisotropy

Magnetic field-driven domain-wall propagation in the flow regime is investigated in (Ga,Mn)As ferromagnetic semiconductor layers. Square-shape magnetic domains with an unexpected orientation of their edges, at π/8 with respect to the anisotropy axes, are found. This is shown to arise from the effect of tetragonal magnetic anisotropy on domain-wall dynamics. Using a one-dimensional model for domain-wall motion and modeling domain growth by contour dynamics the shape and orientation of domains and their field range for existence are well reproduced. These results point to the key role of the vectorial nature of the order parameter in the dynamics of ferromagnetic domains.