Magnetic Phase Diagram of CexLa1-xB6Studied by Static Magnetization Measurement at Very Low Temperatures

DC magnetization of single crystals of Ce x La 1- x B 6 , 0.5≤ x ≤1, have been measured at low temperatures ( T ) down to 40 mK in magnetic field H //[100], and the H - T - x phase diagrams were obtained. At zero field, the antiferro-quadrupolar (AFQ) transition temperature T Q rapidly decreases with decreasing x and vanishes abruptly between x =0.75 and 0.7. The Néel temperature T N , which is lower than T Q in CeB 6 , varies more slowly with x and exceeds T Q for \(x 0.8\). A clear peak observed in the susceptibility strongly suggests that a new antiferromagnetic (AF) state having no AFQ moment (phase IV) exists for \(0.8 x 0.5\), in addition to the two ordered 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 magnetization. Successive I (paramagnetic)-IV-III phase transitions are observable in a very narrow region of the H - T - x space.