Spin susceptibilities in the theory of itinerant-electron antiferromagnetism. II. Two-band incommensurate case

Abstract

For pt.I see ibid., vol.5, p.2343 (1975). The method of calculating the susceptibilities in the spin-density-wave state of an itinerant-electron antiferromagnet introduced in the previous paper is extended to the two-band incommensurate case. The model Hamiltonian used is the Feeders and Martin two-band model in which electrons in different bands are coupled. Both longitudinal and transverse susceptibilities are calculated within the random phase approximation and explicit expressions which do not make any approximation for the form factors are given. The susceptibilities contain both intraband and interband parts. The Coulomb interaction is shown to contribute only to the interband part of the longitudinal susceptibility. The differences between the commensurate and incommensurate spin-density wave states are discussed as well as the collective modes arising from the susceptibilities.