Magnetic Instability of the Gap State in CeNiSn at Very Low Temperature

Abstract

The low-temperature magnetic property of the gap-type Kondo lattice compound CeNiSn has been investigated down to 0.08 K by the 119 Sn nuclear magnetic resonance (NMR) technique. The temperature dependence of 119 Sn nuclear-spin-lattice relaxation rate (1/ T 1 ) down to 0.4 K was well interpreted by a model that the quasi-particle density of states has a V-shaped structure of the pseudogap proportional to the energy in the vicinity of the Fermi level. Below 0.13 K, however, (1/ T 1 ) is found to decrease exponentially as exp(-Δ/ k B T ) due to the appearance of the energy gap of Δ=0.25 K. The NMR spectrum starts to broaden below 0.13 K, signifying that there develops a static magnetic correlation with a magnetic moment estimated to be as small as 10 -3 µ B / Ce atom. It is suggested that the pseudogap state is changed into the “ spin gap ” state induced by the development of the static magnetic correlation.