Dominance of magnetoelastic coupling in multiferroic hexagonal YMnO_3

TL;DR

This study investigates the atomic-level effects of magnetic fields on hexagonal YMnO_3, revealing that exchange-striction plays a dominant role over magnetoelectric coupling in its multiferroic behavior.

Contribution

It provides direct experimental evidence showing exchange-striction's dominance in YMnO_3, highlighting its impact on lattice and magnetic properties under magnetic fields.

Findings

Large variations in lattice parameters near Néel temperature

Magnetic field modifies atomic positions and dielectric constant

Exchange-striction surpasses magnetoelectric coupling in influence

Abstract

Hexagonal YMnO_3 with space group P63cm is one of the rare examples of multiferroic materials that exhibit co-dependence of a robust ferroelectric phase along with antiferromagnetic ordering. This is primarily ascribed to tilting of the MnO_5 polyhedra driven by magnetoelectric coupling. We report on the effect of magnetic field at the atomic level in YMnO_3 by utilizing magnetic field and temperature dependent neutron diffraction measurements. We show that near the N\'eel temperature the lattice parameters, effective magnetic moment per site, Mn-O bond lengths and O-Mn-O bond angles show large variations and these are further modified in the presence of magnetic field. We observe distinct changes with the application of magnetic field in the paramagnetic state both in atomic positions and in the bulk dielectric constant. Our results provide unambiguous confirmation of the role played by exchange-striction over and above the much studied magnetoelectric coupling in this frustrated antiferromagnet.