A MINIATURE CAPACITANCE DILATOMETER FOR THERMAL-EXPANSION AND MAGNETOSTRICTION

A very small capacitive sensor for measuring thermal expansion and mag netostriction of small and irregular shaped samples has been developed . A capacitive method with tilted plates is used. The tilted plate cap acitance formula is used for the calculation of the capacitor gap, the calibration is performed by measuring the signal of a standard materi al. The active length of the sample can be less than 1 mm. The absolut e resolution is about 1 A. All mechanical connections of the dilatomet er 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 0.3-20 0 K and in static magnetic fields up to 15 T. The zero signal of the d ilatometer has been determined by measuring a silver sample. The corre ct operation and reproducibility has been verified by measuring the th ermal expansion of Cu. The thermal expansion and magnetostriction of a DyCu2 single crystal has been determined. The advantage of this metho d compared to specific heat measurements is that a large temperature r ange can be covered with one equipment. This high static and dynamic r ange of sample length, temperature, and magnetic field suggests a numb er of possible applications, like the investigation of crystal field e ffects on the magnetoelastic properties of single crystals or structur al phase transitions. (C) 1998 American Institute of Physics. [S0034-6 748(98)01007-7].