Magnetic and transport properties of antiperovskite nitride Co₃FeN films

Highly spin-polarized ferromagnetic materials have attracted much attention for high-performance spintronic devices. Recently, antiperovskite 3d ferromagnetic nitirides such as Fe₄N and Co_xFe_4-xN are focused because they do not contain rare earth elements and harmful elements. Recent first-principle calculation suggests that Co₃FeN has a high negative spin polarization (P = -1), hence Co₃FeN is most promising material for spintronics ^[1]. Up to now, epitaxial growth and properties of Co₃FeN thin films on SrTiO₃ substrates (lattice mismuch = -3.9%) by molecular beam epitaxy (MBE) were reported^[2]. Recently, we succeeded in epitaxial growth of Co₃FeN thin films on (La_0.18Sr_0.82)(Al_{0. 59}Ta_0.41)O₃ (LSAT) substrates (lattice mismatch = -2.8 %) by reactive magnetron sputtering in Ar+N₂ atmosphere (volume concentration of N₂ gas N₂% = 8∼15% and substrate temperature T_s = 350 °C) ^[3]. The sign and the absolute value of AMR ratio are considered to be strong related to spin polarization ^[4]. We obtained the anisotropic magnetoresistance (AMR) ratio of -0.88% ^[3], so that our Co₃FeN thin film is expected high spin polarization. In this study, we report a systematical study by changing T_s on growth of Co₃FeN thin films on LSAT substrate and its magnetic properties including AMR ratio. As a result, we obtain larger absolute value of the AMR ratio than our previous report. In addition, we succeeded in measuring the spin polarization of Co₃FeN by point contact Andreev reflection. Finally, we would like to discuss the relationship between AMR ratio and spin polarization.