57Fe Mössbauer study of perovskite-type Fe–Ni nitrides γ′-(Fe1−xNix)4N (0⩽x⩽0.8)

Abstract Perovskite-type Fe–Ni nitrides γ′-(Fe 1− x Ni x ) 4 N in the 0⩽ x ⩽0.8 range have been investigated by Mossbauer spectroscopy. Mossbauer spectra have been recorded at low temperatures (4.2 or 20 K), at ∼300 K and above the Curie temperature of each sample. The quadrupole splitting at the Fe II (cube face center) site was large and increased upon Ni substitution, exceeding 1 mm/s. The low-temperature Mossbauer spectra were fitted with magnetic and quadrupole hyperfine interactions combined with a binomial distribution of Ni nearest neighbors. The fitting results indicated that the direction of the easy magnetic axis undergoes a transformation from [0 0 1] to [1 1 1] for increasing Ni substitution. The hyperfine field at Fe I (cube corner) site increased anomalously with x , while it remained nearly constant at Fe II site. The isomer shift did not exhibit any significant change in the whole range of Ni concentration at both Fe I and Fe II sites.