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

Abstract

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.

Iron Nitride Thin Films: Growth, Structure, and Properties

“…There are several reports on the use of sputter deposition for obtaining thin iron nitride films. ,,− The process can be carried out using a dedicated iron nitride target or using pure Fe in a reactive nitrogen-containing atmosphere (in the works included in this Review, only iron deposition in N 2 was used). Owing to the fact that the method is generally mild to the substrate, the films could be grown on all types of supports: (semi)­conducting and insulating, crystalline and amorphous, metal, oxide, polymer, etc.…”

“…Among the reported cases, films on “classical” silicon wafers, SrTiO 3 substrates, MgO, ,, glass, and polyethylene terephthalate (PETE) can be found. Also, different types of buffer layers were used to improve the growth of iron nitride films, including noble metals (Ru, Pd, and Pt) and metal nitrides (TiN, AlN, Cu 3 N). Most of the obtained films represented the γ′-Fe 4 N and γ′′-FeN phases; however, single works reported the formation of γ′′′-FeN, ξ-Fe 2 N, ε-Fe x N, and α′′-Fe 16 N 2 …”

“…The reports on the growth of this phase in different crystallographic directions are extremely rare (see, for example, ref ). Single-phase and single-crystal films are only possible for epitaxial growth on single-crystal substrates, such as MgO(001), Cu(001), Cu(111), LaAlO 3 (001), SrTiO 3 (001), or Ru(0001) thin film . The other relatively commonly occurring phases are the γ′′-FeN, ε-Fe 3‑x N and α′′-Fe 16 N 2 .…”

“…Single-phase and single-crystal films are only possible for epitaxial growth on single-crystal substrates, such as MgO(001), 95 Cu(001), 97 Cu(111), 77 LaAlO 3 (001), 120 SrTiO 3 (001), 82 or Ru(0001) thin film. 89 The other relatively commonly occurring phases are the γ′′-FeN, 41 ε-Fe 3-x N 81 and α′′-Fe 16 N 2 . 105 The films representing ζ-Fe 2 N, 121 α′-Fe 8 N, 107 γ′′′-FeN, 92 and w-FeN 68 constitute very rare cases.…”

Antiperovskite Magnetic Materials with 2p Light Elements for Future Practical Applications

“…[151,152] Although Fe 4 N is not a half-metal, the P DOS (E F ) has been measured to be 61.1-81.3% in a film structure with Cr and Pt underlayers using the method for point contact Andreev reflection. [153,154] Furthermore, the P DOS (E F ) becomes negative as a result of the dominant hybridization between the 2s and 2p orbitals of N and the 4s orbital of Fe. [53] The damping constant of the Fe 4 N/Pt bilayer structure has been measured to range from 0.02 to 0.03, which is dependent on the film thickness of the Fe 4 N layer.…”