MAGNETIC PHASE-DIAGRAMS OF THE DENSE KONDO COMPOUNDS CEB6 AND CE0.5LA0.5B6

We have studied the magnetic phase diagrams of the dense Kondo compoun ds CeB6 and Ce-0.5 La-0.5 B-6 by use of low temperature ultrasonic mea surements. A transition associated with a quadrupolar reorientation ha s clearly been observed around 1 kOe in the antiferroquadrupolar phase II of CeB6. In the paramagnetic phase I of Ce-0.5 Lao(0.5) B-6 a cros sover from the ordinary Gamma(g) ground state to the Kondo singlet sta te has been found. The field induced transition from the Kondo singlet state to the antiferromagnetic phase III or the phase II has been fou nd at a critical field 17 kOe. The field angle dependence of the phase diagram of C-0.5 La-0.5 B-6 is also presented.