On Mn2+ EPR Probing of the Ferroelectric Transition and Absence of Magnetoelectric Coupling in Dimethylammonium Manganese Formate (CH3)2NH2Mn(HCOO)3, a Metal–Organic Complex with the Pb-Free Perovskite Framework

Abstract

We employ electron paramagnetic resonance (EPR) of Mn2+ as a spin probe to study the paraelectric–ferroelectric transition in dimethylammonium manganese formate, [(CH3)2NH2]Mn(CHCO2)3, (DMMnF), which is considered a model metal–organic framework (MOF) with a Pb-free perovskite architecture. We study the variation of the Mn2+ EPR line shape and intensity at the X-band (∼9.5 GHz) over 80 to 300 K. The peaks are essentially Lorentzian, implying electron spin exchange at frequencies greater than 9.5 GHz. On cooling, an anomalous increase in the peak width is noted at 185 K but no anomalous change in the normalized, double-integrated EPR signal intensity around the TC, indicating that DMMnF is transparent to microwave electric fields with a clear lack of magnetoelectric coupling, in contrast to an earlier report. Our analysis enables us to estimate change in lattice strain related to the ferroelectric transition, information that is difficult to obtain by other techniques.