Falaication, magnetic properties, and electronic structures of nanoscale zinc-blende MnAs dots

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NiAs-type Mn pnictide fibres grown on GaAs substrates by molecular-beam epitaxy (MBE) have been extensively studied because of their potential as spintronic device applications utilizing ferromagnetic metal-semiconductor hybrid structures. Among them MnAs and MnSb have a higher potential for spintronic devices due to their high Curie temperatures Tc (MnAs: Tc~320K, MnSb: Tc~600 K). Basic physical properties of MnAs films including the consecutive phase transitions between the NiAs-MnP-liAs type crystalline structures in the bulk have been investigated. The electronic structure of MBE-grown Mn pnictides films has also been investigated by photoemission spectroscopy including spin-resolved measurements.At first, ferromagnetic nanoscale zinc-blende MnAs dots were successfully fabricated on a sulfur-passivated GaAs (001) surface by molecular-beam epitaxy. Transmission electron microscopy and selected area electron diffraction showed that the crystalline structure was not the same as that of bulk MnAs with NiAs-type hexagonal crystalline structure, but of zinc-blende type. In in situ photoemission spectroscopy of the zinc-blende MnAs dots, the Fermi edge was not clearly observed and the Mn 3d partial density of states was similar to that of the diluted ferromagnetic semiconductor Gal-xMnxAs, which also supports the fabrication of zinc-Hende MnAs in the nanoscale.In the second step, we have synthesized Mn-Pt nanoparticles using a chemical preparation based on a liquid-phase reaction caused by decomposition of organometallic precursors. The synthesized monodisperse Mn52.5Pt47.5 nanoparticles show an fcc crystalline structure and ferromagnetic properties even at the room temperature. Mn52.5Pt47.5, which is not ferromagnetic in a bulk form, shows a completely different physical property in nanparticles.