COMPARISON OF MAGNETOCALORIC PROPERTIES FROM MAGNETIC AND THERMAL MEASUREMENTS

The isothermal change of the magnetic entropy of a magnetically ordere d material upon application of external magnetic held can be calculate d from the temperature and field dependence of the magnetization or of the specific heat. The adiabatic temperature change, i.e., the magnet ocaloric effect (MCE) can be measured directly or can be calculated vi a different methods using the field-dependent specific heat values, or a combination of data obtained via magnetization and thermal measurem ents. In the present study, magnetic and thermal measurements were car ried out on Gd75Y25(T-C=232 K) and Gd48Y52(T-C=161 K) samples, for app lied fields ranging between 0 and 7 T. From both datasets, the magneti c entropy change and MCE values were calculated and compared, in order to assess the mutual reliability of the methods applied. The magnetic ally or thermally deduced specific heat discontinuities show a reasona ble agreement within experimental error. Similar comparison of the cal culated magnetic entropy changes reveals that the measured transition temperature and the shape of the curve do not depend on the method sel ected. It is demonstrated that the choice of an integration constant d uring entropy calculation has a significant impact on the adiabatic te mperature change deduced from the held and temperature dependence of t he entropies. For the MCE, a better approximation can be obtained usin g the magnetically acquired magnetic entropy change and the field-depe ndent specific heat. The results prove that magnetic measurements carr ied out in high enough magnetic fields provide reliable information on the isothermal magnetic entropy change and, when combined with field- dependent specific heat measurements, on the magnetocaloric effect as well. (C) 1997 American Institute of Physics.