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

金属间化合物CePdAl是研究铈化合物中4f电子局域化和去局域化中间特性的一个典型例子。然而，当对该样品进行实验时，残余电阻率小于几mΩcm的样品并不好。我们一直专注于这个样品，专注于培养好的单晶样品。我们已经成功地用20μΩcm制备了一个单晶，它在磁场下下降了几个μΩcm，这表明有可能探测到de Haas-van Alphen振荡。本文的主要研究结果如下：1。成功制备了C (Pd_<1-x>Ni_x)Al单晶样品，其中x范围为0.0 ~ 1.0.2。在最低温度为0.1K，最大压力为1.3 GPa，最高场为15 t的极端条件下进行了电阻率、磁化率和比热实验，从这些实验结果中可以发现(1)Neel温度随着压力的增加而平稳降低并消失，(2)同时4f电子的磁化强度减小。这些结果与已建立的Ce（Pd_<1-x>Ni_x）体系相一致。电阻率的温度依赖性显示出T^<1.5>到0.1K的非费米液体行为。但这个特征在7T磁场下瓦解，费米液体行为恢复，即ρ ~ T^2.4。Ce(Pd_<1-x>Ni_x)Al单晶样品的热电功率在x ~ 0.4的100k左右出现了巨大的正值，与临界浓度x_e ~ 0.1相差很大，低温初始斜率dS/dT也在x ~ 0.4处达到最大值。

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.