Heat capacity measurements under pressure are important for studying interaction between physical properties and crystal structures, because pressure can decrease inter-atomic or inter-molecular distance. AC calorimetry is adequate technique for measuring heat capacity under pressure by small amount of sample. Previously, we used ruthenium oxide sensor chips as a proper thermometer at low temperatures. But it has low sensibility in higher temperature. In order to measure heat capacity above 20 K, we chose platinum thin film chip as a thermometer. By the usage of high pressure calorimeter with this Pt chip, we measured heat capacities of Fe3O4 under several pressures. They show single peak at 125.3 K under ambient pressure, and this anomaly broadens gradually with increasing pressures.
Fig.1. Temperature dependence of electronic resistance of Pt chip under various pressures. The temperature dependence of resistance of Pt chip is in proportion to temperature above 20 K. Inset shows the resistance from liquid helium temperature to ambient temperature under ambient pressure.
Fig.2. Magnetic susceptibility of Fe3O4 at ambient pressure. It shows a step like anomaly around 124 K.
Fig.3. Heat capacity of Fe3O4 from 110 K to 140 K under various pressures. The peak structure around 125 K is associated with Verwey transition, and this anomaly broadens gradually with increasing pressure.