Ferromagnetic MnCoGe thin films produced via magnetron sputtering and non-diffusive reaction
Résumé
MnCoGe thin films were produced using simultaneous magnetron sputtering of Mn, Co, and Ge on SiO2, followed by non-diffusive reaction. The MnCoGe compound begins to form at ∼588 K, and structural characterizations show that the obtained MnCoGe film is polycrystalline with the hexagonal Ni2In-type structure. This structure is found to be stable from 873 K down to room temperature, the expected hexagonal/orthorhombic structural transition being prevented. The film exhibits a lower average Mn composition than the standard MnCoGe stoichiometry. Furthermore, small clusters (<3 nm) forming planar distributions parallel to the sample surface are observed. They are regularly located every∼11 nm in the specimen depth. They mainly contain Mn and O atoms. Magnetic characterizations show very good magnetic properties, allowing the perpendicular and parallel magnetocrystalline anisotropy constants to be measured down to 100 K, using the Chappert model to fit ferromagnetic resonance measurements. The film magnetic properties match the properties of bulk stoichiometric MnCoGe in the hexagonal structure, with a Curie temperature of ∼269 K and a negligible coercive field at room temperature. The only difference between the magnetic properties of bulk and thin film specimens appears to be the film shape anisotropy, forcing the internal magnetic field to be contained in the film plane.