Heavy fermion ground states in Th_2Zn_<17>-and BaAl_4-type Ce and U ternary intermetallic

Th_2Zn_<17>-和BaAl_4-型Ce、U三元金属间化合物中的重费米子基态

基本信息

批准号：
07454244
负责人：
KONTANI Masaaki
金额：
$ 0.32万
依托单位：
Nagoya University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
1995
资助国家：
日本
起止时间：
1995 至 1996
项目状态：
已结题

项目摘要

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 … More 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

Th_2Zn_<17>型Ce-和U-三元金属间化合物：Ce_2Cu_xAl_<17-x> (6.75*x*8.25)被发现在低温高磁场结构中结晶为Th_2Zn_<17>型结构。比热、磁化率和电阻率表明近藤温度 T_K 随着 x 的增加而增加，并且所有成分的系统都属于具有超过 1.5 J/K^2mol-Ce 的巨大电子比系数 gamma (=C/T) 的非磁性超重费米子系统使用 Y_2Cu_xAl_<17-x> 的结果估计 f 电子贡献。我们还成功地在U系统中找到了新的重费米子材料U_2Cu_xAl_<17-x> (8*x*11)还获得了U_2Cu_xGa_<17-x> (8*x*12)单晶，其比热低至0.2K，高达5.2 T，显示出-1 J/的极大C/T值。在低于 1 K 的温度下，K^ 2 mol-U 与 -logT 成正比，并且几乎不受高达 5.2 T 的磁场影响，其行为… 更多或与Ce_2Cu_xAl_<17-x>体系表现出类似自旋玻璃的短程磁序以及非费米液体行为。BaAl_4型Ce三元化合物：除了CeCuAl_3单晶的宏观测量外，我们还进行了NMR。通过磁场对晶粒排列样品的 ^<63,65>Cu 和 ^<27>Al 进行测量，我们从这些实验中阐明了这一点。 CeCuAl_3 是一种反铁磁体，尼尔温度为 T_N=2.5K，K vs x 图在每个 Cu 和 Al 位点提供了 H_<hf>，1/T_1 给出了 f 电子态的重要微观方面。NMR 测量还表明。 CeCuAl_3 结晶为 BaNiSn_3 型结构而不是 BaAl_4 型结构我们还成功地用 CeCuGa_3 生长了单晶。我们通过与CeCuAl_3相同的晶体结构并进行了上述测量，明确了CeCuGa_3是T_N=4 K的反铁磁体，并且晶体场分裂中的第一能量分裂DELTA_1为几十度，远大于CeCuAl_3.CeCuAl_3的10K。存在于一个有趣的机制中，其中 T_K、RKKY 交换相互作用 T_<RKKY> 和 DELTA_1。为了研究压力对这种竞争的影响，我们开发了高压核磁共振和强磁化测量系统，在高达 15 kbar 的压力下进行核磁共振测量表明，随着压力的增加，CeCuAl_3 的磁性会受到影响。 10 kbar以上T_K增大，T_N减小，反铁磁态完全消失。CeCu_x(Al,Ga)_<4-x>体系的研究也在进行中。