Ferromagnetic Ordering in a Generalized Hubbard Model

Abstract

The present paper considers ferromagnetic ordering in the Hubbard model generalized by taking into account the inter-atomic exchange interaction and the correlated hopping in a partially filled narrow band. Expressions for the magnetization and for the Curie temperature as functions of model parameters and band filling are obtained in the case of weak intraatomic Coulomb interaction. The condition of ferromagnetic state realization is found. The results obtained indicate the important role of correlated hopping.

Itinerant ferromagnetism of systems with double orbital degeneracy

“…It has also been shown [5] that correlated hopping enhances the tendency to ferromagnetism in the case of a less than half-filled band versus a more than half-filled band. Moreover, due to an additional mechanism of correlated hopping the opposite behaviour can be realized [4] (in this connection see also section 2).…”

“…In the papers [3,4] the generalizations of this theory for the single-band case were carried out by taking into consideration within a Hubbard-like tight-binding Hamiltonian certain matrix elements of electron-electron interaction which provide new mechanisms of ferromagnetism stabilization in metallic ferromagnets. The main result of these works is that the inter-atomic exchange interaction plays an essential role for the appearance of a ferromagnetic state with partial polarization.…”

“…This is confirmed by the fact that ferromagnetism in metals has only been found in systems that have atoms with valence electrons in degenerate orbitals that can support an atomic magnetic moment through Hund's rule. Therefore, the extension of the theory proposed in works [3,4] for systems with orbital degeneracy is a relevant and important task, to which this paper is devoted.…”

Metallic ferromagnetism in a generalized Hubbard model

“…Let us write the Hamiltonian, proposed in Refs. [20,23], generalized by taking into account weak magnetic field…”

“…In this model an electron hopping from one site to another is correlated both by the occupation of the sites involved in the hopping process and the occupation of the nearest-neighbor sites. Taking into account the correlated hopping allows to obtain an additional mechanism [21,22] for the stabilization of ferromagnetic ordering.…”