Temperature Variation of Localized Spin and Phase Transition in Half-Filled Hubbard Band

Abstract

The electronic structure and magnetic properties of a half-filled Hubbard band in the paramagnetic state are studied by means of the functional integral method with the static approximation. The fluctuation of random magnetic fields is taken into account. Temperature variations of the distribution function of random field, density of states, free energy and static spin susceptibility χ( T ) are numerically calculated. No sharp metal-insulator transition is found. In the metallic state, an increase of thermal fluctuations of random magnetic fields associated with a gradual phase transition between the states with and without localized moments is found. It is shown that this increase yields a slight bend in the temperature variation of χ( T ) -1 .