11B NMR study of CexLal1-xB6

We have carried out B-11 NMR experiments on single crystals of CexLa1-xB6 in order to investigate the nature of phase IV. The NMR spectrum undergoes an appreciable broadening by the internal magnetic field as T is lowered in phase IV, and the nuclear spin-lattice relaxation rate, 1/T-1, exhibits a sharp peak around the phase I-IV boundary. Also, in phase III the amplitude of the antiferromagnetic (AFM) moment is large enough even just below the phase IV-III transition, which suggests that the AFM moment grows considerably in phase IV. These results support the view that phase IV is an AFM ordered phase.