Search for Magnetic-Field-Induced-Superconductivity in Heavy Fermion Systems.

在重费米子系统和磁性超导系统中，Tchiki等人预测了在高磁场区域发生重入超导的可能性。这种重入行为称为“magnetic-field-induced-superconductivity”(MFIS).根据他们的预测，Isino等人在Chevrel相化合物Eu_&lt；1-x&gt；SnxMo_6S_7中发现了MFI。然而，在重费米子系统中，MFI还没有被发现。我们进行这个项目是为了弄清Eu_x；1-x&gt；SnxMo_6S_7中MFI的来源，并探索在含有稀土元素(RE)或铀元素的重费米子系统中存在MFI的可能性。测量了化合物Eu_&lt；0.8&gt；Sn_&lt；0.2&gt；Mo_6S_&lt；7-y&gt；Se_y(0在23T以下磁场下的电阻和在6T以下磁场下的比热。比热表现为具有磁矩的^8S_&lt；7/2&gt；中En^&lt；2+&gt；离子的肖特基贡献。此外，我们还观察到了Hyste…在出现超导-正常-超导转变的磁场范围内，电阻更大。这一关于磁滞的结果证明了作用在传导电子自旋上的净磁场的方向与外加磁场的方向相反。从这一事实中，直接证实了该系统中的MFIS的机制是由Jaccarino-Peter效应引发的。2.用电弧熔炼法制备了几种含稀土元素(Ce、La、Yb)和UTX型(T=Pd、Pt、Ni和X=Ge、Si、In)的Th_2Cr_2Si_2型化合物。通过电阻、磁化强度和比热等测试手段对化合物的性能进行了研究。在这些化合物中，Lapd_2Ge_2、YbPd_2Ge_2和UNiSi具有超导电性。当Lapd_2Ge_2和YbPd_2Ge_2表现出通常的类BCS超导电性时，UNiSi表现出较弱的重费米子性质。然而，在我们的样品中没有发现MFIs。对含U的超导化合物的研究仍在继续。较少

In heavy Fermion systems and magnetic superconducting systems, the possibility of the reentrant superconductivity in the high magnetic field region has been predicted by Tachiki et al. This reentrant behavior is called as "magnetic-field-induced-superconductivity"(MFIS). Following their prediction, Isino et al descovered the MFIS in a Chevrel Phase compound, Eu_<1-x>Sn_xMo_6S_7. However, in heavy Fermion systems, the MFIS has not been discovered. We performed this project in order to clarify the origin of the MFIS in Eu_<1-x>Sn_xMo_6S_7 and to search for the possibility of the MFIS in the heavy Fermion systems with rare earth elements (RE) or Uranium element.1. The electrical resistance under magnetic fields up to 23 T and the speciffic heat under fields up to 6 T of the compounds Eu_<0.8>Sn_<0.2>Mo_6S_<7-y>Se_y(0 y 0.7) have been measured. The specific heat shows Schottky contribution due to En^<2+> ions in ^8S_<7/2>, which have magnetic moments. Furthermore we have observed the hyste … More resis of the electrical resistance in the field range where superconductive-normal-superconductive transition appear. This result on the hysteresis prove that the direction of the net magnetic field acting on the conduction electron spins is opposite to that of the applied field. From this fact, it is confirmed directly that the mechanism of the MFIS in this system oiriginates from the jaccarino-peter effect. 2. Several Th_2Cr_2Si_2 type compounds containing rare earth elements (Ce, La, Yb) and UTX type (T=Pd, Pt, Ni and X=Ge, Si, In) compounds were prepared by an arc-melting. The properties of these compounds were investigated by the electrical resistance, magnetization and specific heat measurements. Among these compounds, the superconductivity was observed in LaPd_2Ge_2, YbPd_2Ge_2 and UNiSi. While LaPd_2Ge_2 and YbPd_2Ge_2 show the usual BCS like superconductivity, UNiSi behaves weak heavy fermion properties. however, the MFIS was not found in our samples. Investigations of superconducting compounds containing u are continued. Less