Thin film deposition of Mn$_2$Ga under various growth condition

The tetragonal \emph{DO}$_{22}$ phase of Mn$_{3-x}$Ga is a ferromagnetic Heusler with perpendicular magnetic anisotropy. It has high spin polarization, high Curie temperature and low magnetic moment, and thus becomes a good candidate for spin-transfer-torque magnetic random access memory. This work reports the epitaxial growth of tetragonal Mn$_2$Ga thin films using sputtering method. The effect of various substrates, buffer layers, and substrate temperature on the film roughness is presented and compared. The formation of Mn$_2$Ga islands are observed at the beginning of growth on most buffer layers by reflection-high-energy-electron-diffraction. The smoothest film with root-mean-square roughness 0.10nm is obtained by using Pt buffer layer. The magnetic properties are also compared.