Highly Reduced Saturation Magnetization in Epitaxially Grown Ferrimagnetic Heusler Thin Films

The key of spintronic devices using the spin-transfer torque phenomenon is the effective reduction of switching current density by lowering the damping constant and the saturation magnetization while retaining strong perpendicular magnetic anisotropy. To reduce the saturation magnetization, particular conditions such as specific substitutions or buffer layers are required. Herein, we demonstrate highly reduced saturation magnetization in tetragonal D0₂₂ Mn_3-xGa thin films prepared by rf magnetron sputtering, where the epitaxial growth is examined on various substrates without any buffer layer. As the lattice mismatch between the sample and the substrate decreases from LaAlO₃ and (LaAlO₃)_0.3(Sr₂AlTaO₆)_0.7 to SrTiO₃, the quality of Mn_3-xGa films is improved together with the magnetic and electronic properties. Especially, the Mn_3-xGa thin film epitaxially grown on the SrTiO₃ substrate, fully oriented along the c axis perpendicular to the film plane, exhibits significantly reduced saturation magnetization as low as 0.06 μ_B, compared to previous results. By the structural and chemical analyses, we find that the predominant removal of Mn II atoms and the large population of Mn³⁺ ions affect the reduced saturation magnetization. Our findings provide insights into the magnetic properties of Mn_3-xGa crystals, which promise great potential for spin-related device applications.