1ST NMR OBSERVATION OF VALENCE FLUCTUATION IN RARE-EARTH COMPOUNDS-SE-77 NMR-STUDIES OF TEMPERATURE-ACTIVATED VALENCE FLUCTUATION IN SM3SE4

We have performed Se-77 NMR studies on a semiconducting and valence-fl uctuating compound Sm3Se4 and a reference system Sm2Se3 with particula r emphasis on temperature-and frequency-dependences of the nuclear tra nsverse (1/T2) as well as longitudinal (1/T1) relaxation rates. 1/T2 i n Sm3Se4 shows a dramatic increase with decreasing temperature below 1 60 K, which occurs neither in 1/T1 of Sm3Se4 nor in 1/T2 congruent-to 1/T1 of Sm2Se3. Moreover, marked f2-variation with the resonance frequ ency f has been observed in 1/T2 of Sm3Se4 in this temperature range. Discussions are made on how Se-77 NMR can probe the valence-fluctuatio n (VF) phenomena, and the observed various features of Se-77 NMR are s hown to be explained quite consistently in terms of the temperature-ac tivated VF. As far as the present authors know, this is the first NMR observation of the VF in rare-earth compounds.