Self-thermometry measurements of the adiabatic temperature change in first-order phase transition magnetocaloric materials

TL;DR

This paper presents a novel, simplified method to measure the adiabatic temperature change in magnetocaloric materials using a standard commercial magnetometer, enabling comprehensive characterization of phase transition materials.

Contribution

The authors extend a magnetization-based thermometry technique to first-order phase transition materials, allowing full magnetocaloric characterization with a single, commercially available instrument.

Findings

Achieved accurate $ riangle T_{ad}$ measurements within 1 ext{ } of direct measurements.

Demonstrated the method's applicability to first-order phase transition material Gd$_5$Si$_2$Ge$_2$.

Enabled characterization of magnetic entropy change, heat capacity, and $ riangle T_{ad}$ using one setup.

Abstract

Accurately measuring the magnetocaloric effect is necessary to foster the development of magnetic refrigeration devices. However, current methods are inconvenient, requiring different instruments to measure each individual property or a custom-made setup. By measuring the time-varying magnetization in a commercially available VersaLab\textsuperscript{\textregistered} PPMS\textsuperscript{\textregistered} from Quantum Design, we have determined the adiabatic temperature change ($\Delta$T$_{\textrm{ad}}$) of the first-order phase transition material Gd$_5$Si$_2$Ge$_2$, for a magnetic field change of 0 to 1 T, under high vacuum ($<$ 0.1 mTorr). For each temperature and magnetic field, the equilibrium magnetization is used as the magnetization-to-temperature conversion curve, allowing us to extend the validity of a previously proposed technique to the first-order phase transition material Gd$_5$Si$_2$Ge$_2$, which exhibits significant hysteresis. Our method thus enables full characterization (magnetic entropy change, adiabatic temperature change, and heat capacity) of any magnetocaloric material, whether it has a first-order or a second-order phase transition, using a single instrument. Comparing to a directly measured $\Delta$T$_{\textrm{ad}}$, our method resulted in a peak $\Delta$T$_{\textrm{ad}}$ value of 4.47 K, within 1\% of the directly measured value for a sample of the same composition.