Powder neutron diffraction studies of structure and magnetic Ce ordering in the strongly correlated electron compound Ce0.75La0.2511B6

By means of powder neutron diffraction investigations, chemical structure and magnetic Ce ordering of Ce0.75La0.2511B6 have been investigated at temperatures down to 105 mK. In the antiferromagnetic low-temperature phase III Ce0.75La0.2511B6 resembles pure CeB6, but has a lower Neel temperature TN between 0.89 and 1.25 K. Similar to the recently determined magnetic ordering in pure CeB6 (model C), one obtains the compared to CeB6 smaller ordered magnetic Ce moments μCe(1)=0.53(1) μB at z=0 and μCe(2)=0.12(1) μB at z=1/2 with respect to the magnetic unit cell at 105 mK. Presumably this magnetic ordering, which is characterized by both propagation vectors k=[1/4,1/4,0] and k'=[1/4,1/4,1/2], is caused by competition between magnetic dipole and multipolar ordering. At 0.89 K the magnetic moments are reduced to μCe(1)=0.31(1)μB and μCe(2)=0.08(1)μB. At 1.25 K in phase IV with presumably multipolar Ce ordering no significant magnetic Bragg peaks associated with magnetic dipole Ce moments were observed, supporting the octupole model of Kubo and Kuramoto for this phase