|Budget Amount *help
¥1,900,000 (Direct Cost: ¥1,900,000)
Fiscal Year 1989: ¥100,000 (Direct Cost: ¥100,000)
Fiscal Year 1988: ¥200,000 (Direct Cost: ¥200,000)
Fiscal Year 1987: ¥1,600,000 (Direct Cost: ¥1,600,000)
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
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