Ferroelectricity Driven by Orbital Resonance of Protons in CH${}_3$NH${}_3$Cl and CH${}_3$NH${}_3$Br

Abstract

The $\beta$ and $\gamma$ phases of methylammonium chloride CH${}_3$NH${}_3$Cl and methylammonium bromide CH${}_3$NH${}_3$Br are identified to be ferroelectric $via$ pyroelectric current and dielectric constant measurements. The magnetic susceptibility also exhibits pronounced discontinuities at the Curie temperatures. We attribute the origin of spontaneous polarization to the emergence of two groups of proton orbital magnetic moments from the uncorrelated motion of the CH${}_3$ and NH${}_3$ groups in the $\beta$ and $\gamma$ phases. The two inequivalent frameworks of intermolecular orbital resonances interact with each other to distort the lattice in a non-centrosymmetric fashion. Our findings indicate that the structural instabilities in molecular frameworks are magnetic in origin as well as provide a new pathway toward uncovering new organic ferroelectrics.

5 pages, 5 figures

References in corpus (3)

• Magnetic Ordering of Ammonium Cations in NH${}_4$I, NH${}_4$Br and NH${}_4$Cl
• Magnetoelectric Coupling Based on Protons in Ammonium Sulfate
• Magnetic Properties of NH${}_4$H${}_2$PO${}_4$ and KH${}_2$PO${}_4$: Emergence of Multiferroic Salts

Cited by in corpus (1)

• Magnetic interactions based on proton orbital motion in CH${}_3$NH${}_3$PbI${}_3$ and CH${}_3$NH${}_3$PbBr${}_3$