Spin-spiral states in undoped manganites

TL;DR

This paper investigates the origin of spin-spiral states in undoped manganites, showing they arise from intermediate Hund's rule and Jahn-Teller couplings, supporting a spin-current mechanism for ferroelectricity.

Contribution

It demonstrates that spin-spiral and E-type phases can occur in a standard two-band model without relying on frustrating superexchange couplings.

Findings

Spin-spiral phases with diagonal wavevector exist at intermediate couplings.

Supports the spin-current mechanism for ferroelectricity.

Provides an alternative to superexchange-based explanations.

Abstract

The experimental observation of multiferroic behavior in perovskite manganites with a spiral spin structure demands to clarify the origin of these magnetic states and their relation to ferroelectricity. We show that spin-spiral phases with diagonal wavevector and also the E-type phase exist for intermediate values of the 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 obtain spin-spiral states.