Deposition and spin polarization study of Fe₄N thin films with (111) orientation

We have successfully deposited Fe₄N thin films with (111) out-of-plane orientation on thermally oxidized Si substrates using a facing-target-sputtering system. A Ta/Ru composite buffer layer was adopted to improve the (111) orientation of the Fe₄N thin films. The N₂ partial pressure and substrate temperature during sputtering were optimized to promote the formation of the Fe₄N phase. Furthermore, we measured the transport spin polarization of (111) oriented Fe₄N by the point contact Andreev reflection (PCAR) technique. The spin polarization ratio was determined to be 0.50 using a modified BTK model. The film thickness dependence of the spin polarization was also investigated. The spin polarization of Fe₄N measured by PCAR does not show degradation as the sample thickness was reduced to 10nm.