THE ISOTHERMAL MAGNETOCALORIC COEFFICIENT

Tomasz Plackowski

   A simple method of in-magnetic-field calorimetric measurements is presented. It is based on commercial Peltier elements used as sensitive heat-flow meters of high thermal conductivity. In the presented experimental setup the Peltier element thermally connects the sample to a heat sink of constant temperature. Application of the magnetic field (B) ramp results in the sample temperature change due to magnetocaloric effect, but, due to high thermal conductivity of the Peltier element, any temperature difference is quickly thermalized. The ensuing heat flux, detected as a voltage on the Peltier element terminals, is proportional to a quantity called the isothermal magnetocaloric coefficient, M_T. It could be measured quasi-continuously up to the maximum field attainable by the superconducting magnet used in the experiment (B_max = 13 T in our case). The available temperature range spans between 20 and 300 K. The obtained set of M_T(B) curves holds a valuable information on magnetic and thermodynamic properties of the matter. It is particularly useful if compared with the set of specific heat curves C_B(T) taken at constant field, which could be obtained using the very same experimental setup. Several examples of the behavior of the isothermal magnetocaloric coefficient for various magnetic (Mn_0.9Co_0.1P and UAs_0.97Se_0.03 single crystals) and superconducting (YBa₂Cu₃O_7-δ single crystal and Bi2223 tape) materials are given.

Keywords: magnetocaloric effect, specific heat, heat-flow meters, heat-flow calorimetry

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