GaMnAs is a model system for diluted ferromagnetic semiconductors. The origin of ferromagnetism is the exchange interaction between the carriers and the Mn 3d spins with exchange constant Jpd. The phosphorous alloying of GaMnAs is used as a novel practical technique to adjust the magnetic anisotropy. It provides layers with perpendicular anisotropy with high homogeneity. The spin-stiffness constant A is determined and the field-driven domain wall dynamics is investigated using Kerr microscopy. In GaMnAsP due to the low density of defects the magnetic domains form a self-organized pattern....