Study of magnetocaloric effects on rare-earth and iron compounds for room temperature magnetic refrigeration

点击翻译按钮获取中文摘要

In recent years, there has been increasing interest in magnetic refrigeration as an environmentally friendly alternative to conventional vapor-cycle refrigeration. The magnetic refrigeration makes use of the cycles of magnetization and demagnetization of a magnetic material, so that the development of new materials with a giant magnetocaloric effect (MCE) is strongly desired. In the previous research project of Grant-in-aid for scientific research (09555185), we have pointed out that the first-order phase transition system would show giant MCEs. In this study, we investigated MCEs of the compounds with T_c at around room temperature. The following results were obtained.1) We started our research from focusing our attention on the compounds with rare-earths and iron. First, We measured the magnetic entropy change, ΔS_M, caused by a magnetic field. Of R_2Fe_<17> compounds (R=Pr, Ce and Ce_<0.5>Nd_<0.5>) and Gd Laves phase compounds (Gd(Co-Ni)_2 and Gd(Al-Fe)_2). However, these compounds … More show at most 6 J/K kg of ΔS_M, at the peak value, which is less than half of that of Gd.2) Then, we searched a first-order phase transition system and found MnAs. This compound shows a first-order ferromagnetic to paramagnetic transition at 317 K. The observed ΔS_M is 32 J/K kg, which is 1.7 times as large as that of Gd_sSi_2Ge_2. These results indicate that MnAs shows giant MCEs. We also found the substitution of Sb for As can tune the Curie temperature between 220 K and 317 K without any significant reduction of MCEs. These results indicate that MnAs_<1-x>Sb_x is one of the most suitable candidates for the magnetic refrigerant material at room temperature.3) During the present research, the Chinese group reported a large MCE of La(FeCoSi)_<13>. However, a detailed magnetic phase diagram was not investigated. We studied the magnetic properties of La(Fe_<0.88>Si_<0.12-x>Co_x)_13. The compounds form a NaZn_<13>-type structure for 0【less than or equal】x【less than or equal】0.05. The Curie temperature is increased from 195 K to 260 K with increasing x from 0 to 0.05. Metamagnetic behavior was observed above T_c in the concentration range of 0【less than or equal】x【less than or equal】0.05. These results suggest large magnetocaloric effects of the present system at around room temperature. Less