A setup for direct measurement of the adiabatic temperature change in magnetocaloric materials

In order to find a highly efficient, environment-friendly magnetic refrigerant, direct measurements of the adiabatic temperature change $\mathrm{\Delta }{T}_{adb}$ is required. Here, in this work, a simple setup for the $\mathrm{\Delta }{T}_{adb}$ measurement is presented. Using a permanent magnet Halbach array with a maximum magnetic field of $1.8$ T and a rate of magnetic field change of $5$ T/s, accurate determination of $\mathrm{\Delta }{T}_{adb}$ is possible in this system. The operating temperature range of the system is from $100$ K to $400$ K, designed for the characterization of materials with potential for room temperature magnetic refrigeration applications. Using the setup, the $\mathrm{\Delta }{T}_{adb}$ of a first-order and a second-order compound have been studied. Results from the direct measurement for the first-order compound have been compared with $\mathrm{\Delta }{T}_{adb}$ calculated from the temperature and magnetic field dependent specific heat data. By comparing results from direct and indirect measurements, it is concluded that for a reliable characterization of the magnetocaloric effect, direct measurement of $\mathrm{\Delta }{T}_{adb}$ should be adopted.