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Search for Regenerative Materials with Large Specific Heat Based on Rare Earth-Manganese Compounds

寻找基于稀土锰化合物的大比热蓄热材料

基本信息

批准号：
04555155
负责人：
SHIGA Masayuki
金额：
$ 7.68万
依托单位：
KYOTO UNIVERSITY
依托单位国家：
日本
项目类别：
Grant-in-Aid for Developmental Scientific Research (B)
财政年份：
1992
资助国家：
日本
起止时间：
1992 至 1994
项目状态：
已结题

项目摘要

In recent years, much attention has been paid to rare earth (R) compounds with large specific heat at low temperatures as magnetic regenerative materials, because of the spread of small cryocooler and superconducting magnets. In the RMn_2 compounds, both R and Mn have large magnetic moments in spite of their low magnetic ordering temperatures. We have examined low temperature specific heat and related properties of this system in order to develop new regenerative materials. The following results were obtained :(1) In the case of Al substitution for Mn, the system shows spin glass at low temperatures. The specific heat and entropy become very large above 50K,but they are not enhanced at low temperatures.(2) On the other hand, in the compounds with smaller atomic distance such as HoMn_2 and ErMn_2, most of Mn atoms are nonmagnetic. Large spin fluctuations were observed in these compounds, which enhance electronic specific heat at low temperatures.(3) The crystal field is also an important factor for large specific heat. The analyzes of crystal field were developed and were successfully applied to RCo_2 and RMn_2Ge_2 compounds.Base on these results, we conclude that Cu and Ni substitution for RMn_2 is a candidate for new regenerative materials, which is under investigation. We also found that a suitable material is expected for(Dy-Er)Bi compounds.

近年来，由于小型制冷机和超导磁体的推广，低温比热大的稀土化合物作为磁蓄冷材料受到了广泛关注。在RMn_2化合物中，尽管R和Mn的磁有序温度较低，但它们都具有大的磁矩。为了开发新的蓄热材料，我们研究了该系统的低温比热和相关性质。结果表明：（1）Al替代Mn时，体系在低温下表现为自旋玻璃。比热和熵在50 K以上变得很大，但在低温下并不增加。(2)而在原子间距较小的化合物如HoMn_2和ErMn_2中，大部分Mn原子是双价的。在这些化合物中观察到大的自旋涨落，这在低温下提高了电子比热。(3)晶体场也是比热大的一个重要因素。本文发展了晶场分析方法，并成功地应用于RCo_2和RMn_2Ge_2化合物的研究，结果表明，Cu、Ni替代RMn_2是一种新的蓄热材料，目前正在研究中。我们还发现，一个合适的材料是预期的（Dy-Er）Bi化合物。