Thin-film alternating current nanocalorimeter for low temperatures and high magnetic fields

Abstract

Thin-film nanocalorimeter for low temperatures and high magnetic fields is described. The calorimeter is based on a commercial microchip module (thermal conductivity vacuum gauge TCG 3880 from Xensor Integration, NL). The gauge consists of submicron silicon nitride membrane with a film-thermopile and a resistive film-heater with dimensions of 50×100μm2 located at the center of the membrane. The gauge is mounted in a thermostat filled with helium exchange gas. The method of alternating current (ac) calorimetry is applied for heat capacity measurements. The noise-floor sensitivity of the calorimeter is better than 1nJ∕K below 100K and about 3nJ∕K at 300K. This allows for reliable measurements to be performed on sub-microgram samples. It is proved that the method is applicable for heat capacity measurements at temperatures in the range of 5–300K and in high magnetic fields up to 8T. We present a theoretical analysis of the thermal processes in the gauge-sample-surrounding gas system. On this basis a calibration method has been developed. We demonstrate that the technique yields correct heat capacity for test samples and that in special cases the thermal conductivity and the magnetostriction of the sample can be measured simultaneously with the heat capacity.