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

近年来，人们对磁制冷越来越感兴趣，认为它是传统蒸汽循环制冷的一种环保替代品。磁致冷利用磁性材料的充磁和退磁循环，因此开发具有巨磁热效应（MCE）的新材料是迫切需要的。在之前的科研资助项目（09555185）中，我们已经指出一阶相变体系会出现巨大的mce。在本研究中，我们研究了含T_c化合物在室温左右的mce。得到了以下结果：我们的研究是从把注意力集中在稀土和铁的化合物上开始的。首先，我们测量了磁场引起的磁熵变化ΔS_M。R_2Fe_<17>化合物（R=Pr， Ce和Ce_<0.5>Nd_<0.5>）和Gd相化合物(Gd（Co-Ni)_2和Gd(Al-Fe)_2）。然而，这些化合物…More在峰值时最多显示6 J/K kg ΔS_M，不到gd的一半。2)然后，我们搜索了一个一级相变体系，并找到了MnAs。该化合物在317k时表现出一级铁磁到顺磁的跃迁。观测到的ΔS_M为32 J/K kg，是Gd_sSi_2Ge_2的1.7倍。这些结果表明MnAs表现出巨大的MCEs。我们还发现Sb取代As可以将居里温度调节在220 K到317 K之间，而不会显著降低mce。结果表明，MnAs_<1-x>Sb_x是室温下磁性制冷剂最合适的候选材料之一。3)在本研究中，中国组报道了La（FeCoSi）的大MCE _<13>。然而，没有研究详细的磁相图。我们研究了La(Fe_<0.88>Si_<0.12-x>Co_x)_13的磁性能。在0【小于等于】x【小于等于】0.05的范围内，化合物形成NaZn_<13>型结构。当x从0增加到0.05时，居里温度从195 K增加到260 K。在T_c以上，在0【小于等于】x【小于等于】0.05的浓度范围内，观察到变磁行为。这些结果表明，当前系统在室温左右存在较大的磁热效应。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