| Research Abstract |
Th_2Zn_<17>-type Ce- and U- ternary intermetallic compounds : Ce_2Cu_xAl_<17-x> (6.75*x*8.25) was found to crystallize in the Th_2Zn_<17>-type structure. The low temperature and high magnetic fields specific heats, magnetic susceptibility and electrical resistivity indicated that the Kondo temperature T_K increases with x and the system for all the compositions belong to non-magnetic super-heavy-fermion system with giant electronic specific coefficients gamma (=C/T) over 1.5 J/K^2mol-Ce. The f-electron contributions were estimated using the results of Y_2Cu_xAl_<17-x> as a non-magnetic reference. We also succeeded in finding new heavy fermion materials in U-system, U_2Cu_xAl_<17-x> (8*x*11) and U_2Cu_xGa_<17-x> (8*x*12). The single crystals were also obtained. The specific heat down to 0.2K and up to 5.2 T revealed that the extremely large C/T values of -1 J/K^2 mol-U are proportional to -logT at temperatures below 1 K and are little affected by magnetic fields up to 5.2 T,which behavi
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ors are quite contrary to Ce_2Cu_xAl_<17-x> system. These systems showed short range magnetic orders like spin-glasses as well as the non-Fermi-liquid behavior.
BaAl_4-type Ce ternary compounds : In addition to macroscopic measurements of CeCuAl_3 single crystals, we performed NMR measurements of ^<63,65>Cu and ^<27>Al for a grain-aligned sample by magnetic fields. From these experiments we clarified that CeCuAl_3 is an antiferromagnets with a Neel temperature of T_N=2.5K and the K vs x plot provided H_<hf> at each Cu and Al site and the 1/T_1 gave important microscopic aspects of f-electron states. The NMR measurements also suggested that CeCuAl_3 crystallizes in the BaNiSn_3 type structure rather than BaAl_4-type. We also succeeded in growing single crystals of CeCuGa_3 with the same crystal structure as CeCuAl_3 and performed the above measurements. We clarified that CeCuGa_3 is an antiferromagnet with T_N=4 K and the first energy splitting DELTA_1 in the crystal field splitting is several tens of degrees, which is much larger than 10K for CeCuAl_3.
CeCuAl_3 lies in an interesting regime with competing T_K, RKKY exchange interaction T_<RKKY> and DELTA_1, each other. In order to investigate the effect on pressure against this competition, we developed high pressure NMR and magnetization measurement systems. The NMR measurements in pressures up to 15 kbar revealed that the magnetic properties of CeCuAl_3 are strongly influenced by pressure. With increasing pressure, the value of T_K increases and T_N decreases, and the antiferromangetic state disappeared completely above 10 kbar. The study of CeCu_x (Al, Ga)_<4-x> system are also in progress. Less
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