LAUSR

Abstract The essential step for epitaxial growth of tetragonal Mn3Ge films with high perpendicular magnetic anisotropy (PMA) is to choose suitable substrates with small lattice misfit. The exploration process has involved large efforts on depositing films on single crystalline substrates using buffer layers preferably formed from Cr or Pt, but they lacked a systematically comparative investigation for practical applications. This study investigates the structural, surface and magnetic properties of ultrathin Fe (2 nm) seed layer to induce homoepitaxial Mn3Ge films on MgO (0 0 1) substrates compared with that of the heteroepitaxial Mn3Ge films on three typical buffer layers, such as Cr (40 nm), Cr (20 nm)/Pt (10 nm), Fe (2 nm)/Pt (20 nm). Furthermore, a correlation between film strain and film quality has been established, which is critical for spintronics applications. More importantly, we attribute the homoepitaxial growth of Mn3Ge films on the ultrathin Fe seed layers to the Fe diffusion and formation of Fe-Mn-Ge alloy at the interface, and confirm this supposition with HAADF-STEM characterizations. The Fe-doped Mn3Ge interlayer can act as the gradual buffer layer, and lead to a high-quality crystal structure and extremely high magnetic squareness ratio of Mn3Ge films in a large range of thickness (100 ~ 400 nm). This result offers a new concept of high-quality growth of D022-Mn3Ge films, which may enhance the prospect for tetragonal Mn3Ge thin films in superior spintronics applications.