DUALITY OF LOCALISED AND DE-LOCALIZED CHARACTERS OF 4F ELECTRONS IN CERIUM COMPOUNDS

金属间化合物CePdAl是研究4f电子在铈化合物中局域化和离域化之间的中间特征的典型例子。然而，当在该样品上开始实验时，不存在具有小于几个mΩcm的残余可渗透性的良好样品。我们专注于这个样品，集中精力生长出好的单晶样品。我们已经成功地制备了一个20μΩcm的单晶，它在磁场下下降了几个μΩcm，这表明有可能检测到de Haas-van Alphen振荡。主要结果如下：1.成功地制备了C（Pd_<1-x>Ni_x）Al单晶样品，其中x的范围为0.0 ~ 1.0.2。在最低温度0.1K、最高压力1.3GPa、最高磁场15 T的极端条件下进行了电磁化率、磁化率和比热实验。实验结果表明：（1）Neel温度随压强的增加而平滑地降低和消失，（2）同时4f电子的磁化强度减弱。这些结果与Ce（Pd_ Ni_x）Al体系的结果一致<1-x>。当温度T_i降低到0.1K时，其电导率随温度的变化表现为非费米液体行为<1.5>。但是，在磁场7 T下，这种特性崩溃，并且费米液体行为复活，即，ρ = 2.4。Ce（Pd_ Ni_x）Al单晶样品的热电势<1-x>在100 K附近在x = 0.4时出现巨大的正值，与临界浓度x_e = 0.1相差甚远，低温下的初始斜率dS/dT也在x = 0.4时出现极大值。

The intermetallic compound CePdAl is a typical example to study intermediate characters between localization and de-localization of 4felectrons in the cerium compound. However, there was not good sample with a residual resistibility less than a few mΩcm when the experiments started on this samples. We have focused on this sample and concentrated ourselves to grow good single-crystalline samples. We have succeeded to prepare a single crystal with 20μΩcm, and it drops a few μΩcm under magnetic fields, suggesting a possibility to detect the de Haas-van Alphen oscillations. Main results obtained here are as follows:1. Single crystalline samples of C (Pd_<1-x>Ni_x)Al have been successfully prepared, where x ranges from 0.0 to 1.0.2. The electrical resistibility, magnetic susceptibility, and specific heat experiments have been carried out under the extreme conditions, the lowest temperature 0.1K, the maximum pressure 1.3 GPa and the highest field 15 T. From these experimental results, it is found that (1) the Neel temperature smoothly decreases and disappears as the pressure increases, (2) at the same time the magnetization of 4f electrons diminishes. These results are consistent with those of the instituted systems of Ce(Pd_<1-x>Ni_x)Al.3. The temperature dependence of the electrical resistibility shows non-Fermi liquid behaviors as T^<1.5> down to 0.1K. But this character collapses under the magnetic field 7T, and a Fermi liquid behavior revives, i.e., ρ〜T^2.4. The thermoelectric power of single crystalline samples of Ce(Pd_<1-x>Ni_x)Al shows huge positive value around 100 K in x 〜 0.4 far different from the critical concentration x_e 〜 0.1, and the initial slope dS/dT at low temperatures also makes a maximum at x 〜 0.4.