Molecular beam epitaxy growth and characterization of self-assembled MnAs wires on highly oriented pyrolytic graphite

The authors have grown MnAs on highly oriented pyrolytic graphite (HOPG), a strain-free and inert substrate, using molecular beam epitaxy. MnAs on HOPG grows in the form of particles, which self-assemble to form wirelike structures along the step edges on the HOPG surface. The MnAs particles have an average height of 42 nm and a diameter of 240 nm. Vibrating sample magnetometry studies indicate that the samples are ferromagnetic with no observable in-plane anisotropy, which is expected from a sample with a random distribution of particle orientations. Magnetic force microscopy (MFM) results indicate that the magnetic coupling between particles is less than that within each particle, and likely a dipole-dipole interaction, giving rise to magnetization patterns for the wires. Temperature dependent MFM measurements yield a Curie temperature of 330 K. Scanning tunneling microscopy and scanning tunneling spectroscopy were used to investigate the electronic density of states of MnAs, with the well-studied HOPG surface as a convenient reference.