title: Spin-spiral states in undoped manganites: role of finite Hund's rule coupling.
abstract: The experimental observation of multiferroic behavior in perovskite manganites with a spiral spin structure requires a clarification of the origin of these magnetic states and their relation to ferroelectricity. We show that spin-spiral phases with a diagonal wave vector and also an E-type phase exist for intermediate value of Hund's rule and the Jahn-Teller coupling in the orbitally ordered and insulating state of the standard two-band model Hamiltonian for manganites. Our results support the spin-current mechanism for ferroelectricity and present an alternative view to earlier conclusions where frustrating superexchange couplings were crucial to obtaining spin-spiral states.
authors.affiliation: Institute Lorentz for Theoretical Physics, Leiden University, P.O. Box 9506, 2300 RA Leiden, The Netherlands.
authors.forename: Sanjeev
authors.initials: S
authors.lastname: Kumar
authors.forename: Jeroen
authors.initials: J
authors.lastname: van den Brink
authors.forename: Arno P
authors.initials: AP
authors.lastname: Kampf