Effect of Magnetic Field on the Magnetic Domain Structure of MnAs Film on GaAs(001)

We have observed the magnetic domain evolution under an external magnetic field in an epitaxial MnAs film on GaAs(001) by magnetic force microscopy. Owing to the strain involved, the ferromagnetic alpha-MnAs and the paramagnetic beta-MnAs phases coexist as self-aligned stripes at room temperature. It was found that a complex magnetic domain structure appeared in the ferromagnetic alpha-phase region at the demagnetized state (H=0 Oe). As the magnetic field increased, the magnetic domain structure was gradually changed, and reached a completely saturated state at H=600 Oe. Especially, at H=300 Oe, the observed magnetic domain wall distribution is well matched with the topographical shape.