57Fe Mossbauer study of perovskite-type Fe-Ni nitrides γ′-(Fe1-xNix)4N (0 ≤ x ≤ 0.8)

Perovskite-type Fe-Ni nitrides gamma'-(Fe1-xNix)(4)N in the 0 less than or equal to x less than or equal to 0.8 range have been investigated by Mossbauer spectroscopy. Mossbauer spectra have been recorded at low temperatures (4.2 or 20 K), at similar to 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. (C) 2000 Elsevier Science B.V. All rights reserved.