Thes-f model with Coulomb repulsion: Thermodynamics of two atomic cluster. Spin 1/2

Abstract

A cluster of two atoms described by thes-f model with Coulomb repulsion has been considered. The interaction between localized 4f electrons (S=1/2) is taken in the molecular field approximation. The thermodynamic quantities like magnetization, specific heat and correlation functions 〈n ↑〉, 〈n ↓〉, 〈S z n ↑〉, 〈S z n ↓〉, 〈S z (n ↑−n ↓)〉, 〈n ↑ n ↓〉 and 〈S + a ↓ + a ↑〉 as functions of temperature are presented for different band fillingN=0, 0.5, 1, 1.5, 2. The dependence of Curie temperature onN is calculated. The phase diagram forN=1 (T=0K) shows the possibility of existence of two phases: paramagnetic and ferromagnetic. The Curie temperature and the specific heat as functions ofN exhibit similar trends as found in experiments on doped magnetic semiconductors.