| Multiferroic materials are rare compounds featuring at least two ferroic properties with a majority of them displaying (anti)ferro – electricity or magnetism. Currently, the most famous compounds displaying such behavior are oxide perovskites. One of the most common mechanisms for ferroelectric behavior in perovskites, requires an empty d-orbital which usually means that the material is diamagnetic. Hence there is a need for multiferroic materials in which two independent mechanisms can determine the electric and magnetic ordering. I was able to achieve this using hybrid perovskites.;Hybrid perovskites of general formula (CH3)2NH 2M(HCOO)3 have a ReO3 type cage made up of formate and metal ions. The metal ions sit at the corners of the cubes and are connected to each other via coordination bonding with oxygen of the formate ion. The dimethylammonium cation is located at the center of this cavity. The amine hydrogen atoms make hydrogen bonds with the oxygen atoms of the metal formate framework. Because of this hydrogen bonding, the nitrogen of the ammonium cation is disordered over three equal positions at room temperature. Cooling down these materials below 180 K leads to a lowering in symmetry, a result of the ordering of nitrogen atoms.;This phase transition is associated with a dielectric anomaly. Carefully done dielectric measurements show that the anomaly is a λ-type peak usually associated with paraelectric to ferroelectric phase transition. Low temperature single crystal measurements aided by powder X-ray diffraction and neutron diffraction experiments show that low temperature phase crystallizes in monoclinic symmetry and Cc space group. Cc belongs to one of the 10 polar point groups which are requirements for ferroelectricity. Furthermore, magnetic fields seem to affect this dielectric anomaly, suggesting that these hybrid perovskites have a magnetodielectric effect. This phase transition was studied in detail by electron paramagnetic resonance, heat capacity, and 1 H NMR relaxation time measurements.;Close to 0 K, specific heat data suggest that there is a remnant specific heat, a classic signature of amorphous or glassy materials. NMR data shows that these hybrid materials are indeed glassy below 40 K with many confirmations with close underlying energies. This effect is related to the rotation of methyl motors. NMR results also show an anomaly at the same temperature where dielectric anomaly is present. Methyl protons slow down by a factor to suggest that dielectic anomaly is indeed due to the ordering of nitrogen atoms. |
