Complex Spin Structures and Origin of the Magneto-Electric Coupling in YMn2O5

TL;DR

This study uncovers the complex spin arrangements in YMn2O5 using neutron diffraction, revealing spiral magnetic structures that elucidate the origins of its magneto-electric coupling and phase transition behaviors.

Contribution

It provides detailed magnetic structures of YMn2O5's ferroelectric phases, supporting multiple microscopic theories of magneto-electric coupling.

Findings

Magnetic structures include spiral components in both phases.

Results support spin-current and magneto-restriction models.

Explains polarization change at phase transition.

Abstract

By combining neutron four-circle diffraction and polarized neutron diffraction techniques we have determined the complex spin structures of a multiferroic, YMn2O5, that exhibits two ferroelectric phases at low temperatures. The obtained magnetic structure has spiral components in both the low temperature ferroelectric phases that are magnetically commensurate and incommensurate, respectively. Among proposed microscopic theories for the magneto-electric coupling, our results are consistent with both the spin-current model that requires a magnetic transverse (cycloidal) spiral structure in order to induce a spontaneous electric polarization and the magneto-restriction model. Our results also explain why the electric polarization changes at the commensurate-to-incommensurate phase transition.