Theory of Finite-Temperature Magnetism of NiMn. II. Bethe Theory, Susceptibility and Atomic Short Range Order

Abstract

The molecular-field-type theory of the local environment effect proposed previously is extended up to the Bethe approximation, and the magnetism of NiMn alloys is further investigated by using both the Bethe theory and the molecular-field theory. The susceptibility, the phase diagram and the magnetization-temperature curves are obtained as functions of the concentration and the atomic short range order (ASRO). It is found that they strongly change with the ASRO. A reasonable explanation of the experimental susceptibilities is obtained by taking the ASRO into account. Experimental T c and the magnetization curves with the change of the ASRO are also well explained by the theory. Present theory shows that the spin-glass temperatures T g are largely reduced with the atomic ordering and that the inflections of the susceptibility at T g are rather small in NiMn alloys.