Metallic magnetism and magnetic volume collapse

Abstract

We present a new description of possible magnetovolume instabilities in itenerant electron systems based on a generalized Ginzburg-Landau expression. The Landau coefficients are input data and are obtained by reproducing binding surfaces (total energies as function of volume and the magnetic moment), which are the result of spin-polarized band structure calculations performed with the fixed-spin-moment (FSM) method. Finite temperature results are obtained by constructing a classical field theory. It is shown that essentially two Landau parameters (the fourth-order coefficient and the critical volume) may serve to classify itinerant magnetic systems as stable or potentially instable systems. In the first category the magnetic phase transition is of second order while, in the latter, the transition can be of first order, associated with a large magnetic volume collapse. We show that all INVAR systems are potentially instable.