MAGNETOCALORIC EFFECT OF Gd_5Si_2Ge_2 AND ITS CHARACTERISTICS UNDER DIFFERENT OPERATING CONDITIONS

摘要

Magnetocaloric effect (MCE), or adiabatic temperature change, and thermal hysteresis were directly measured for the first order magnetocaloric Gd_5Si_2Ge_2 material. The experiments were conducted under different operating conditions over the temperature range from 258 K to 276K with the magnetic field change rates varying from 0.25 T/s to 6 T/s. Some interesting phenomena were observed. The magnetocaloric effect measured during heating with initial sample temperature progressively increasing is different from that for the cooling experiments when the sample temperature was progressively reduced. The maximum MCE in the cooling mode is significantly higher than that observed for the heating mode; the temperature of the MCE peak for the cooling mode is also shifted downward by 2.5 K compared to that for the heating mode. In this study, the MCE was also compared for various magnetic field change rates to understand time dependence of the MCE. The information obtained in this study is helpful in optimizing operation of the magnetic refrigeration cycle and tailoring magnetocaloric materials for specific applications.