Magnetic Field Evolution of a Novel Phase Transition in CeOs4Sb12: 121Sb NMR Study

We report on the evolution of a novel phase transition under magnetic field ( H ) in the filled skutterudite compound CeOs 4 Sb 12 probed by 121 Sb NMR. Measurements of nuclear spin–lattice relaxation rate 121 (1/ T 1 ) for the oriented powder with H ∥[100] have revealed that antiferromagnetic (AFM) spin fluctuations due to the proximity of a quantum critical point at H =0 are markedly suppressed by the application of H , which is consistent with the result indicating that the AFM order at T N =0.9 K with a very small moment of 0.07µ B collapses, exceeding H =1 T. As H increases further, a large reduction in 1/ T 1 T was observed below the temperature T 0 , which varies as a dome against H with a maximum of 1.8 K at H ∼6 T. The values of T 1 T =const. well below T 0 decrease with increasing H , indicating that the residual density of states depends on H . It is suggested that the field-induced novel transition is associated with the freezing of multipole degree of freedom.

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