Simple NarrowBand Model of Ferromagnetism Due to IntraAtomic Exchange
Abstract
As a model of ferromagnetism due to intraatomic exchange, we consider a narrow band with two orbital states, such as d_{z2} states in a bcc lattice. We include hopping and intraatomic Coulomb and exchange terms in the Hamiltonian. If we assume that the hopping process does not change the orbital state, it is found for one electron per atom and for sufficiently narrow bands that it is energetically favorable for two sublattices to form, each with predominantly one of the orbital states, and for the spins to line up ferromagnetically. We use the randomphase approximation to extend this result beyond the narrowband limit. The stability of this ferromagnetic state is investigated by calculating its spinwave spectrum, and the region of stability as well as the effective exchange parameter depend on the strength of the intraatomic exchange integral. For one electron per atom, the mechanism is too weak for real ferromagnets, but it becomes stronger for less than one electron per atom.
 Publication:

Physical Review
 Pub Date:
 September 1966
 DOI:
 10.1103/PhysRev.149.306
 Bibcode:
 1966PhRv..149..306R