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

近年来，磁制冷作为传统蒸气循环制冷的一种环境友好的替代方案越来越受到人们的关注。磁制冷利用了磁性材料的磁化和退磁循环，因此迫切需要开发具有巨磁热效应(MCE)的新材料。在上一个科研资助项目(09555185)中，我们已经指出，一阶相变系统将出现巨型MCEs。在本研究中，我们研究了具有T_c的化合物在室温附近的MCEs。取得了以下研究成果：1)我们的研究从关注稀土和铁的化合物开始。首先，我们测量了磁场引起的磁熵变ΔS_M。R_2Fe_&lt；17&gt；化合物(R=Pr，Ce和Ce_&lt；0.5&gt；ND_&lt；0.5&gt；)和Gd Laves相化合物(Gd(Co-Ni)_2和Gd(Al-Fe)_2)。然而，这些化合物…ΔS_M的峰值最大为6J/K kg，不到Gd的一半。2)然后，我们搜索一级相变系统，发现了MNAs。该化合物在317K出现一级铁磁-顺磁转变，观测到的ΔS_M为32J/K kg，是Gd_SSI_2Ge_2的1.7倍。这些结果表明MNAs是巨大的MCEs。我们还发现，Sb取代As可以在220~317K之间调节居里温度，而不会显著降低MCEs。这些结果表明，MNAs_(FeCoSi)_1-x&gt；Sb_x是最合适的室温磁致冷材料之一。3)在本研究中，中国小组报道了La(FeCoSi)_(13)&gt；然而，详细的磁相图并未被研究。我们研究了La(Fe_&lt；0.88&gt；Si_&lt；0.12-x&gt；Co_x)_13的磁性。当0[小于或等于]x[小于或等于]0.05时，化合物形成NaZn_&lt；13&gt；型结构。随着x从0增加到0.05，居里温度从195K增加到260K。在T_c以上，在0[小于或等于]x[小于或等于]0.05的浓度范围内观察到了超磁行为。这些结果表明，本系统在室温附近有很大的磁热效应。较少

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