Simple practical system for directly measuring magnetocaloric effects under large magnetic fields.

Direct measurements of the adiabatic temperature change (ΔT) in Gd and MnFePSiC are made using a homemade adiabatic magnetocalorimeter at 260-360 K and 0-7 T. The system uses a servo motor to drive the samples into and out of the magnetic field under a vacuum environment provided by the Physical Property Measurement System (PPMS). The peak values of ΔT for Gd and MnFePSiC at 7 T are 8.71 K and 6.41 K at ambient temperatures of 303 K and 317 K, respectively. Based on the theory model, it is found that ΔT of Gd depends on the 2/3 exponential function of magnetic field H (ΔT ∝ H), whereas the MnFePSiC compound follows the power law of ΔT ∝ H due to the first order magnetic transitions. Furthermore, using the constructed experimental instrument, the adiabatic temperature change in different magnetic materials, including materials with first/second order magnetic transition and blocks, flakes, or powders, can be directly measured under large magnetic fields and wide temperature spans.