Mössbauer Study of Hyperfine Fields and Isomer Shifts inFe4N and(Fe,Ni)4N

Abstract

M\ossbauer measurements of ${\mathrm{Fe}}^{57}$ were made on ferromagnetic ${\mathrm{Fe}}_{4}$N, which has a face-centered cubic arrangement of iron atoms with nitrogen at the body-center position. The hyperfine fields are 345 koe for the corner Fe and 215 koe for the three face-center Fe, approximately proportional to their magnetic moments, $3{\ensuremath{\mu}}_{B}$ and $2{\ensuremath{\mu}}_{B}$. The isomer shifts, measured against a stainless steel source, are 0.30 mm/sec for the corner Fe and 0.45 mm/sec for the face-center Fe. These values are in line with their proposed electronic configurations of $3{d}^{7}4s$ and $3{d}^{8}4s$, which are derived on the assumption that the nitrogen at the body-center position acts as an electron donor to the face-center Fe. The M\ossbauer spectra of (${\mathrm{Fe}}_{3.6}$,${\mathrm{Ni}}_{0.4}$)N and (${\mathrm{Fe}}_{3}$Ni)N are consistent with their ordered structures in which Ni replaces the corner Fe preferentially.