A Microscopic Model for Ferromagnetism of UGe₂

Abstract

We construct a microscopic Hamiltonian for the ferromagnetism of UGe₂ by taking account of the orbital degeneracy of the 5-f electrons and investigate possible phases by the Hartree–Fock approximation. We reduce the number of mean values to be determined by assuming the magnetic orders where the coplanar magnetic moments perpendicular to the c-axis constitute an a-axis moment as a whole. Because of the orbital degeneracy, the anisotropies of the crystalline electric field term and the hopping term competes with each other. Moreover occupation number in each atomic orbit is sensitive to the relation between the crystalline electric field and the Coulomb interaction. In consequence, a rich ground state phase diagram with various different ferromagnetic orders is obtained.