Epitaxial ferromagnetic MnAs thin films grown on Si(001): The effect of substrate annealing

We have studied two different types of epitaxial ferromagnetic MnAs thin films on Si (001) substrates grown by molecular beam epitaxy. When the Si substrates were annealed at a relatively high temperature (similar to 900 degrees C) and then MnAs was grown, we obtained epitaxial MnAs films with twofold crystal symmetry (type I). In contrast, when the thermal cleaning of the Si substrate was done at a lower temperature (similar to 600 degrees C), epitaxial MnAs thin films had fourfold crystal symmetry (type II). The growth plane in both types of MnAs thin films was the ((1) over bar 101) of the hexagonal MnAs. The type I MnAs films are single domain with strong magnetic anisotropy, whereas the type II MnAs films are double domain with the lack of strong magnetic anisotropy. (C) 1996 American Institute of Physics.