Easy-axis changes in perovskite-type Fe-Ni nitrides gamma '-(Fe1-xNix)(4)N: A Mossbauer study

Perovskite-type Fe-Ni nitrides gamma'-(Fe1-xNix)(4)N have been investigated by Mossbauer spectroscopy in the 0 less than or equal to x less than or eq ual to 0.8 concentration range. Mossbauer spectra have been recorded at low temperatures and above the Curie temperature of each compound. The quadrup ole splitting at the FeII (cube face center) site was large and increased u pon Ni substitution, exceeding 1 mm/s. The low-temperature Mossbauer spectr a were fitted with a full Hamiltonian model combined with a binomial distri bution of Ni nearest neighbors. The fitting results indicated that the dire ction of the easy magnetic axis undergoes a continuous rotation from [100] to [111] for increasing Ni concentration. This result is discussed in terms of possible changes in the K-1/K-2 ratio upon Ni substitution. (C) 2000 Am erican Institute of Physics. [S0021- 8979(00)79508-9].