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Magnetostriction and Effect of Pressure on the Thermal Expansion Coefficient of the Dense-Kondo Compounds

磁致伸缩和压力对致密近藤化合物热膨胀系数的影响

基本信息

批准号：
62540219
负责人：
OOMI Gendo
金额：
$ 1.22万
依托单位：
Kumamoto University (1988-1989)Hokkaido University (1987)
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (C)
财政年份：
1987
资助国家：
日本
起止时间：
1987 至 1989
项目状态：
已结题

项目摘要

Results obtained here are summarized as follows. (1)Electrical Resistivity From the measurement of electrical resistivity of single crystalline CeCu_6 along b-axis, alpha (T),the resistivity -maximum temperature T_m(K) is found to increase from 15 K at 1 bar to 90 K at 30 kbar by applying pressure. Since T_m is proportional to Kondo temperature T_k,the result indicates that T_k increases with pressure. The pressure coefficient of T_m,T_m,^<-1> delta T_m/delta P,is estimated to be 170X10^<-3> kbar^<-1>. On the other hand,the value for CePd_3 is 6.5X10^<-3> kbar^<-1>,which is smaller than that of CeCu_6 by an order magnitude. We suggested that this may arise from the difference in the pressure dependence of s-f exchange interaction in these materials.(2)Thermal Expansion The thermal expansion coefficient of single crystalline CeCu_6, alpha_i (i=a,b or c),is found to be strongly anisotropic:alpha_b is largely affected by the crystal electric field (CEF) and alpha_c increases with decreasi … More ng temperature below 10 K due to Kondo effect.In the plot of alpha/T vs T^2 (alpha=(1/3) (alpha_a + alpha_b + alpha_c)),a large increase in the magnitude of alpha/T is found at low temperatures corresponding to a large enhancement in the value of C/T. This is originated from the large enhancement of effective mass at low temperatures.The same results were obtained in CeInCu_2 and CeAl_3.A Schottky type anomaly is observed in the alpha -T curve above 10 K,where alpha is the magnetic contribution to alpha.By applying the phenomenological theory of Ohkawa,we can estimate two CEF splitting energies of CeCu_6.(3)X-ray Diffraction The lattice constants of CeCu_6,a,b and c,are measured as a function of pressure P(kbar) at room temperature and 77.4 K.A large anisotropy is found in the pressure dependence of a,b and c,i,e.,the compressibilities kappa_a,kappa_b and kappa_c.The order of magnitude is kappa_b > kappa_c > kappa_a. The result is in qualitative agreement with that obtained by ultrasonic measurement.A second order phase transition is found near 45 kbar at 77.4 K. Less

这里获得的结果总结如下。（1）电阻率通过测量单晶CeCu_6沿着b轴的电阻率α（T），发现通过施加压力，电阻率-最高温度T_m（K）从1巴下的15 K增加到30千巴下的90 K。由于T_m与近藤温度T_k成正比，结果表明T_k随压力增大而增大。压力系数T_m，T_m，Δ <-1>T_m/Δ P，估计为170 × 10 ~ 4 ^<-3>kbar^<-1>。另一方面，CePd_3的值为6.5 × 10 ~ <-3>4 kbar ~ 4<-1>，比CeCu_6的值小一个数量级。我们认为，这可能是由于这些材料中s-f交换相互作用的压力依赖性的差异。（2）热膨胀CeCu_6单晶的热膨胀系数α_i（i=a，B或c）具有很强的各向异性：α_i（i=a，B或c）受晶体电场（CEF）的影响很大，α_c随晶体电场（CEF）的减小而增大。 ...更多信息在α/T对T^2（α =（1/3）（α_a + α_B + α_c））的关系图中，发现在低温下α/T的幅度大幅度增加，对应于C/T的大幅度增加。在CeInCu_2和CeAl_3中也得到了同样的结果.在10 K以上的α-T曲线上观察到了Schottky型反常，α是磁场对α的贡献.应用Ohkawa的唯象理论，我们可以估算出CeCu_6的两个CEF分裂能.（3）X射线衍射在室温和77.4 K下测量了CeCu_6的晶格常数a、B和c随压力P（kbar）的变化，发现a、B和c随压力的变化具有很大的各向异性，压缩系数kappa_a、kappa_B和kappa_c的大小顺序为kappa_B > kappa_c > kappa_a。实验结果与超声测量结果定性一致，在77.4 K时，在45 kbar附近发现了二级相变。少