Magnetic refrigerant properties of Mn-Pnictides showing giant magnetocaloric effecits

近年来，磁制冷作为一种环境友好的替代传统蒸汽循环制冷的方法受到越来越多的关注。为了实现磁制冷，人们迫切需要具有巨磁热效应的新材料。2001年，我们发现<1-x>0 ≤ x ≤ 0.3的MnAs_ Sb_x化合物在230 ~ 315 K之间表现出巨大的MCE。在本研究中，我们进行了详细的测量MnAs_ Sb_x的磁热性能<1-x>，这是在各种不同的条件下制备的。结果表明：（1）<1-x>当Mn略有富集时，MnAs_ Sb_x形成单一的NiAs型结构。结果表明，Mn_（1+δ）As_ Sb_x中的Mn原子占据了NiAs型结构的间隙位。2）研究了热处理对Mn_（1+δ）As_ Sb_x磁性转变的影响<1-x>。结果发现，从熔融状态淬火和随后的退火是重要的，以实现尖锐的磁性转变。X射线衍射测量揭示了本发明化合物的一级磁性转变（FOMT）。3<1-x>）直接测量<ad>了Mn_（1 + δ）As_<1-x>Sb_x（x=0.1和0.25）化合物的绝热温度变化ΔT。对于这两种化合物，<ad>在磁场变化为5 T时，ΔT =10 K。这些都是Mn_（1+δ）As_Sb_x的巨大MCE的直接证据<1-x>。4）我们还研究了其它具有FOMT的化合物，如Mn_3GaC，Ho（CoNi）_2和Co（SSe）_2的MCE。从这些结果中，我们可以得出结论，过渡金属基化合物是本质上的优势，在室温附近的巨型MCE。

In recent years, there has been increasing interest in magnetic refrigeration as an environmentally friendly alternative to conventional vapor-cycle refrigeration. In order to realize magnetic refrigeration, new materials with giant magnetocaloric effects(MCEs) are strongly desired. In 2001, we have found that MnAs_<1-x>Sb_x compounds with 0【less than or equal】x【less than or equal】0.3 exhibit giant MCEs between 230 K and 315 K. In this research, we performed detailed measurements of magnetocaloric properties on MnAs_<1-x>Sb_x, which were prepared in various different conditions. Following results were obtained.1)We found that MnAs_<1-x>Sb_x forms a single phase with NiAs-type structure, when Mn was slightly enriched. The results suggest that some Mn atoms occupy the interstitial site of the NiAs-type structure, as observed in the case of Mn_<1+δ>Sb.2)Effects of heat treatment on the magnetic transition of Mn_<1+δ>As_<1-x>Sb_x were examined. It was found that quenching from a melted state and subsequent annealing are important to realize a sharp magnetic transition. X-ray diffraction measurements have revealed a first-order magnetic transition(FOMT) of the present compounds. We believe that FOMT is responsible for giant MCEs in Mn_<1+δ>As_<1-x>Sb_x.3)Direct measurements of the adiabatic temperature change, ΔT_<ad>, were carried out for Mn_<1+δ>As_<1-x>Sb_x compounds with x=0.1 and 0.25. For both compounds, we obtained ΔT_<ad> =10 K in a field change of 5 T. These are direct evidence of giant MCEs of Mn_<1+δ>As_<1-x>Sb_x.4)We examined MCEs of other compounds showing FOMT, such as Mn_3GaC,Ho(CoNi)_2 and Co(SSe)_2. From these results, we can conclude that the transition metal based compounds are essentially advantage for giant MCEs near room temperature.