Research of New type of Superconductors in Tetragonal HoCoGa5-type Crystal Structure

四重HoCoGa_5型晶体结构是AuCu_3型结构的四重变体，在AuCu_3型结构中发现了新的超导体。CeMIn_5（M：Co，Rh，Ir）化合物表现出许多有趣的性质，如非s-超导性，在上临界场附近的一级跃迁，重费米子行为，压力诱导超导性等。在奇异重费米子超导体中，库珀对是由磁自旋涨落交换形成的，其中非简单定域的f-电子起着重要作用。反常重费米子超导体的特征是在正常态下具有较大的比热系数和居里-外斯行为，或具有较低的反铁磁有序温度。PuCoGa_5和PuRhGa_5被称为重费米子“高T_c”超导体。在Pu基化合物中，Pu的价态为Pu^<3+>（5f^5），Pu^<4+>（5f^4），Pu^<5+>，Pu^<6+>，Sm的价态为Sm^<2+>（4f^6），Sm^<3+>（4f^5）。Sm^<3+>（4f^5）和Pu^<3+>（5f^5）离子具有相同的J=5/2多重态，并表现出局域矩行为，即，服从居里-外斯定律有趣的是，Sm化合物是否表现出奇异行为取决于特定的晶体结构。SmMIn_5（M：Co，Rh，Ir）。单晶SmCoIn_5的物理性质未见报道。对SmMIn_5进行了比热测量、磁化强度测量和电阻率测量。SmRhIn_5和SmIrIn_5在T_N以下表现出反铁磁有序和额外的相变，这与以前报道的结果基本一致。SmCoIn_5在T_N 11.9K以下也表现出反铁磁有序和额外的相变.这些异常的温度分别为6，7.6和11.9K，最低的出现在SmMIn_5化合物中。

The tetragonal HoCoGa_5-type crystal structure is known as a tetragonal variant of the AuCu_3-strucuture in which new superconductors were discovered. CeMIn_5 (M : Co, Rh, Ir) compounds exhibit a variety of interesting properties such as non-s-superconductivity, a first-order transition near the upper critical field, heavy-fermion behavior, pressure-induced superconductivity, etc. In the exotic heavy fermion superconductors, Cooper pairs are expected formed by the exchange of magnetic spin fluctuations, in which f-electrons which are not simply localized play an important role. A large specific heat coefficient and Curie-Weiss behavior in the normal state or low anti-ferromagnetic ordering temperatures are features of the exotic heavy fermion superconductors. PuCoGa_5 and PuRhGa_5 are known as heavy fermion "high T_c" superconductors. Pu has valence states of Pu^<3+>(5f^5), PU^<4+>(5f^4), PU^<5+>, Pu^<6+> in Pu-based compounds, while Sm has Sm^<2+>(4f^6), Sm^<3+>(4f^5). Sm^<3+>(4f^5) and Pu^<3+>(5f^5) ions have the same J=5/2 multiplet, and show the local moment behavior, i.e., obey a Curie-Weiss law. It is interesting that it depends on the particular crystal structure whether Sm compounds show exotic behavior or not.We have succeeded in growing single crystals of. SmMIn_5 (M : Co, Rh, Ir) by the flux method. There was no report of the physical properties on single crystalline SmCoIn_5. Specific heat measurement, magnetization measurements and electrical resistivity measurements were performed on SmMIn_5.SmRhIn_5 and SmIrIn5 showed the antiferromagnetic ordering and extra transitions below T_N, which is almost same as the results in the previous report. SmCoIn_5 also showed the antiferromagnetic ordering and extra transitions below T_N 11.9 K. The temperatures of these anomalies are 6, 7.6 and 11.9 K and lowest found in SmMIn_5 compounds.