Mössbauer study on epitaxial Co_xFe_{4- x}N films grown by molecular beam epitaxy

We prepared Co_xFe_{4- x}N (x = 0, 1, 3) films on SrTiO₃(STO)(001) substrates by molecular beam epitaxy. The epitaxial relationship with Co_xFe_{4- x}N[100](001) || STO[100](001) was confirmed by ω-2θ (out-of-plane) and ∅-2θ_χ(in-plane) x-ray diffraction (XRD) measurements. The degree of order of atoms (S) in the Co_xFe_{4- x}N films was estimated to be ∼0.5 by the peak intensity ratio of Co_xFe_{4- x}N(100) (superlattice diffraction line) to (400) (fundamental diffraction line) in the ∅-2θ_χXRD patterns. Conversion electron Mössbauer spectroscopy studies for the Co_xFe_{4- x}N films revealed that some N atoms are located at interstitial sites between the two nearest corner sites in the Co_xFe_{4- x}N films, and/or Fe atoms are located at both the corner and face-centered sites in the CoFe₃N and Co₃FeN films. In order to realize high spin-polarized Co_xFe_{4- x}N films having large S, further optimization of growth condition is required to prevent the site-disorders.