Miniaturized calorimeters for high pressure, strong magnetic field, and low temperature conditions

by Neha Kondedan (Student)

Wednesday 4 Jun 2025, 09:00 → 12:00 Europe/Stockholm

Albano 2: Sal 4 (Albano Building 2)

Abstract
Calorimetry is a powerful approach for investigating condensed matter systems, with nanocalorimetry being particularly
useful for studying small samples, with high resolution and accuracy. This thesis presents the development of
nanocalorimeters specifically designed for extreme conditions, such as high pressure, strong magnetic fields, and low
temperatures. Introducing high pressure or magnetic fields as tuning parameters in specific heat measurements at low
temperatures can enhance the understanding of the underlying physical properties of novel materials.
Two distinct nanocalorimeters are built and discussed in this thesis; one for sample rotations in high magnetic fields
and another for high-pressure applications. The high-field nanocalorimeters are fabricated on SiNx membranes for specific
heat measurements down to 30 mK. Miniaturization is performed to extend their use for angular-dependent measurements
in high magnetic fields, so far used up to 41 T. In contrast, the high-pressure nanocalorimeters are fabricated on a robust
substrate, which is small enough to fit inside small sample volumes of high-pressure cells. The key component of a
calorimeter is a thermometer. Both these calorimeters use a newly developed thin film ceramic metal oxide thermometer,
which shows high sensitivity and minimal magnetoresistance across a wide temperature range.
A high-pressure setup is designed for transport and AC calorimetry measurements under elevated pressures. This setup
employs a split gasket approach that incorporates multiple electrical connections entering the sample volume through a
substrate. This setup reaches moderate pressures comparable to those in standard setups using similar anvils, with the
advantage of reusable and easily reproducible components.
Finally, specific heat measurements of Eu-doped GdCd7.88 quasicrystals and GdCd6 approximant systems are performed
in fields up to 12 T, using a membrane-based nanocalorimeter. The results show the presence of spin-glass behavior in the
quasicrystals and an antiferromagnetic transition in the approximant crystals at low temperatures.