IMF2017

We employ electron paramagnetic resonance (EPR) of Mn²⁺ as a spin probe to study the paraelectric−ferroelectric transition in [(CH₃)₂NH₂]Mn(CHCO₂)₃, (DMAMnF) and [(CH₃)₂NH₂]Zn(CHCO₂)₃ (DMAZnF dopped Mn²⁺) , which are considered a model metal−organic framework (MOF) with a Pb-free perovskite architecture. In DMAMnF, 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 the ferroelectric transition temperature Tc=185 K but no anomalous change in the normalized, double-integrated EPR signal intensity around the Tc , indicating that DMAMnF is transparent to microwave electric fields with a clear lack of magnetoelectric coupling, in contrast to an earlier report. In DMAZnF, the multifrequency EPR of the Mn²⁺ probe shows the motional dynamics of the DMA+ cation during the cooling down process. We show that depending on the time scale of the measure, the DMA+ is considered moving or frozen. We show that the sudden change of the EPR linewidth when crossing the ferroelectric transition is not due to the freezing of the DMA+ cation but to a ferroelastic transition.