Perpendicular magnetic anisotropy properties of tetragonal Mn₃Ga films under various deposition conditions

The tetragonal Mn₃Ga films exhibited high perpendicular magnetic anisotropy, low saturation magnetization, and high spin polarization, which satisfy the criteria of spin-transfer-torque based devices. For practical device applications, it is necessary to improve the interface nature and optimize the deposition conditions. We fabricated thin films of tetragonal Mn₃Ga directly on MgO(100) without any buffer layer by using DC/RF magnetron sputtering method. We investigated the crystallinity, microstructure, and magnetic properties with varying the deposition conditions; such as deposition temperature (350-450 °C), RF power (25-40 W), and Ar gas pressure (2-7 mTorr). X-ray diffraction data revealed that the growth direction is perpendicular to the film plane, i.e., the c axis. Scanning electron microscope images showed that the top surface is flat with a maximum thickness of 290 nm. The optimal deposition conditions are 400 °C, 35 W, and 5 mTorr in our sputtering system. For the field perpendicular to the film plane, clear hysteresis loop was observed with the saturation magnetization M_S = 100 emu/cc at room temperature. By extrapolating the hard magnetization data for the field parallel to the film plane, the anisotropic energy was estimated about K₁ = 1 × 10⁶ J/m³.