Magnetic domains in epitaxial nanomagnets with uniaxial or fourfold crystal anisotropy

In order to prepare submicron sized particles with strong magnetocrystalline anisotropies high quality epitaxial bcc-Fe films were grown on GaAs(110) and GaAs(001) by molecular beam epitaxy. Whereas Fe(110) on GaAs(110) is a model system with uniaxial in-plane anisotropy, Fe(001) on GaAs(001) has a strong fourfold anisotropy for films thicker than ${\approx}$5 nm. Various shapes like circular, square, or rectangular elements with sizes from 200 nm up to 6 µm were fabricated by electron beam lithography and ion beam etching. The remanent states after saturation along different directions or ac demagnetization along the easy axis were examined by using magnetic force microscopy. The experimental results clearly reflect the interplay of the different magnetocrystalline and shape anisotropies depending on the different magnetic histories.