Simultaneous in-situ specific heat and x-ray diffraction measurements on Fe₂P

The hexagonal transition metal pnictide Fe₂P undergoes both a structural and a magnetic phase transition at 217 K. Strong magneto-elastic coupling turns the usually 2^nd order paramagnet-to-ferromagnet transition into a 1^st order one, making this material a perfect candidate to study the interplay between phase transitions. By integrating a nanocalorimeter platform into a 4.5 T magnet at an x-ray beamline, we have measured the sample’s specific heat and x-ray diffraction simultaneously. This multi-modal approach confirms that the structural and magnetic transitions appear at the same temperature. We observe that applying an external magnetic field broadens the structural transition. Additionally, we investigated the hysteresis of the transition in both specific heat and lattice parameter where the precise temperature control of the nanocalorimeter allows to line up the features observed in both quantities. X-ray scans were taken at different temperatures through the transition which reveal peak splitting in the FM phase that persists into the superheated region indicating the appearance of twinning or a domain structure.