MAGNETIC PHASE-DIAGRAM OF CEXLA1-XB6 STUDIED BY STATIC MAGNETIZATION MEASUREMENT AT VERY-LOW TEMPERATURE

DC magnetization of single crystals of CexLa1-xBF6, 0.5 less than or e qual to x less than or equal to 1. have been measured at low temperatu res (T) down to 40 mK in magnetic field H//[100], and the H - T - x ph ase diagrams were obtained, At zero field. the antiferro-quadrupolar ( AFQ) transition temperature T-Q rapidly decreases with decreasing x an d vanishes abruptly between x = 0.75 and 0.7. The Neel temperature T-N , which is lower than T-Q in CeB6, varies more slowly with x and excee ds T-Q for x greater than or similar to 0.8. A clear peak observed in the susceptibility strongly suggests that a new antiferromagnetic (AF) state having no AFQ moment (phase IV) exists for 0.8 greater than or similar to x greater than or similar to 0.5, in addition to the two or dered phases II (AFQ) and III (AF+AFQ). As H increases, a first-order phase IV-III transition is observed with a metamagnetic jump in the ma gnetization. Successive I (paramagnetic)-IV-III phase transitions are observable in a very narrow-region of the H - T - x space.