A miniature capacitance dilatometer for thermal expansion and magnetostriction

Abstract

A very small capacitive sensor for measuring thermal expansion and magnetostriction of small and irregular shaped samples has been developed. A capacitive method with tilted plates is used. The tilted plate capacitance formula is used for the calculation of the capacitor gap, the calibration is performed by measuring the signal of a standard material. The active length of the sample can be less than 1 mm. The absolute resolution is about 1 Å. All mechanical connections of the dilatometer are carried out by tiny Cu–Be springs, enabling the small force on the sample to be adjusted (50–500 mN) and no additional sample fixing is necessary. The cell has been tested in the temperature range 0.3–200 K and in static magnetic fields up to 15 T. The zero signal of the dilatometer has been determined by measuring a silver sample. The correct operation and reproducibility has been verified by measuring the thermal expansion of Cu. The thermal expansion and magnetostriction of a DyCu2 single crystal has been determined. The advantage of this method compared to specific heat measurements is that a large temperature range can be covered with one equipment. This high static and dynamic range of sample length, temperature, and magnetic field suggests a number of possible applications, like the investigation of crystal field effects on the magnetoelastic properties of single crystals or structural phase transitions.