Magnetization switching depending on magnetic fields applied to ferromagnetic MnAs nanodisks selectively-grown on Si (111) substrates

We report on the applied external magnetic field, B, dependence of a magnetic domain structure and magnetization switching in MnAs nanodisks on AlGaAs nanopillar buffers selectively grown on Si (111) substrates partially covered with dielectric SiO2 thin film mask patterns by selective-area metal–organic vapor phase epitaxy. The results on the B dependence of magnetic domain structures observed by magnetic force microscopy show that the ratio, or percentage, of a single magnetic domain is minimized at B = −1.5 kG in the nanodisks with an area of 4 × 104 nm2 or smaller, although the decrease to the minimum of the ratio is markedly small in the case of the nanodisks with an area of 4 × 104 nm2 or larger at B = −0.5 kG. The angle distribution of magnetization directions shows that the magnetization directions markedly tend to be parallel to the ridge directions of the hexagonal nanodisks, i.e., distribute in steps of ∼60° corresponding to the magnetic easy axes of the hexagonal NiAs-type crystal structure. The results suggest that the magnetic domains and coercive force can be tuned by controlling the MnAs nanodisk size.