NMR Study of a Valence Fluctuating Compound SmB_6

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The "B NMR in a typical valence fluctuating compound SmB, has beeninvestigated in the temperature range between 2.5 and 850 K by the pulsed NMRtechnique. An unusual temperature dependence was observed in the nuclear5pin-lattice relaxation rate (1/T.). l/7'. increases rapidly with increasing tempera-ture above about 20 K, but it remains almost constant above room temperature.This behavior is qualitatively explained by assuming a simple model density of4f states with a gap of 50 K at the Fermi level and a band width of 500 K. Con-trary to the case of usual semiconductors, the experimental result shows thatanother relaxation process sets in that gives a temperature independent relaxa-tion rate below 6 K. Although the physical mechanism of this process has not' been made clear yet, it is proposed that it may be due to the formation of chargelocalized states which are related to the conductivity at low temperatures.
社団法人日本物理学会の論文
1981-08-15