Effects of short-range order and long-range order on the low-temperature specific heat of Ni3Fe alloys

Abstract

Low‐temperature measurements of the specific heat of configurationally long‐range ordered and short‐range ordered NiFe alloys are presented, for the composition range from 70 to 75 at% Ni. The low‐temperature specific heat is given by the equation cp = γT + βT3 + αT3/2, the terms corresponding to the electronic, lattice, and spin‐wave contributions, respectively. It is clear that a spin‐wave term is necessary to explain the experimental results. The coefficients γ and β decrease significantly both with short‐range ordering and long‐range ordering. The variation with composition of γ and of the Debye temperature θD (deduced from β) is determined. The change in γ and θD on long‐range ordering is found to remain the same in the composition range investigated. The change in the Debye temperature on ordering is consistent with the change in the elastic properties. The effects on the electronic term are mainly associated with changes in the density of states at the Fermi level. The results are discussed in terms of the existing theoretical calculations for the effect of ordering on the electronic structure of Ni3Fe.