Ferroelectricity and lattice distortion associated with spin orderings in a multiferroic delafossite AgFeO2

Abstract

Spin-lattice coupling and ferroelectric polarization associated with the magnetic ordering in a geometrically frustrated delafossite AgFeO2 have been studied by high resolution neutron powder diffraction and dielectric measurements. The cycloidal magnetic ground state found in this material and the character of the lattice distortions are unprecedented in the family of the delafossite compounds, implying a peculiar mechanism lifting the geometrical frustration.