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Appearance of Successive Phase Transition in SmRu4P12 under High Magnetic Fields Probed by 31P Nuclear Magnetic Resonance

The 31P-NMR (nuclear magnetic resonance) measurements of the filled skutterudite SmRu4P12 have been carried out in several applied magnetic fields. The line width of the 31P-NMR spectrum rapidly increases below the metal-insulator transition temperature TMI, which indicates the appearance of an internal field below the temperature. Though no distinct anomaly was observed below TMI in low fields, a complicated structure was observed between the Neel temperature TN and TMI (TN < TMI) above 70 kOe. The spin-lattice relaxation rate 1/T1 is almost independent of temperature above TMI, and rapidly decreases below TMI. The 1/T1 in low fields decreases monotonously, whereas the strong suppression of 1/T1 occurs between TN and TMI above 70 kOe. The structure of the spectra and the suppression of 1/T1 become apparent with increasing field.