On the influence of the reservoir and of the shape of the Fermi surface on the phase diagram of two-band models for Cr alloys

Abstract

The Landau expansion around the triple point for a class of mean-field two-band modes including Rice's (1970) unequal-sphere model and the octahedron model of Shibatani et al (1969) is studied with the infinite-lifetime approximation and neglecting magnetostriction. It is shown that, when the reservoir is considered correctly, with reasonable values of the parameters one can obtain a phase diagram in agreement with experiment, i.e. a narrow first-order transition from the paramagnetic to an incommensurate antiferromagnetic phase for nearly pure Cr and a second order paramagnetic to commensurate phase transition accompanied at lower temperature by a wide first-order commensurate-incommensurate transition for Mn-rich Cr alloys. The temperature dependence of the wavevector in the incommensurate phase is also shown to be in qualitative agreement with experiment.