Deuterium ordering found in new ferroelectric compound Co2(OD)3Cl

Abstract

A detailed temperature-dependent Raman spectroscopic study revealed a new type of deuterium-order ferroelectrics in a geometrically frustrated magnet Co _2 (OD) _3 Cl at T _ϵ = 229 K. Significant changes in the parameters of the Raman vibration modes were observed near T _ϵ , suggesting a strong phonon-charge coupling. Additional asymmetric phonon bands appeared below around T _ϵ , which are consistently interpreted by phonon folding processes due to a small local structural change resulting from the ordering of deuterium. The wavenumber and intensity changes of the Raman-active modes, as well as the normalized intensities of the additional bands, all follow a power-law fit Δω , ΔI , I ∝ (1 − T / T _C ) ^2 ^β , wherein T _C = 230 K ∼ T _ϵ and β = 0.35(2), clearly demonstrating an ordering process below T _ϵ . The critical exponent is reminiscent of a second order transition. Our study presents a rare and new type of multiferroic material with ferroelectricity arising from the deuterium ordering in geometrically frustrated magnets.

Keywords

• deuterium ordering
• ferroelectric
• geometric frustration
• deuteroxyl salt