Novel Phase Transition in CeRu2Al10Probed by27Al-NQR/NMR –No Evidence of Magnetic Ordering–

The 27 Al-NQR/NMR measurements of CeRu 2 Al 10 were carried out to clarify the unusual phase transition at T 0 =27 K. Distinct NQR peaks associated with five nonequivalent Al sites have been observed at T > T 0 , and each peak is successfully assigned to their respective Al sites. Below the transition temperature T < T 0 , each peak simply splits into two peaks except for one site. This indicates that the phase transition is not accompanied by magnetic order, but is presumably associated with the onset of structural transition with lowering symmetry. The nuclear spin–lattice relaxation rate 1/ T 1 suggests a local moment picture above T * ∼60 K, and the development of Kondo coherence toward T 0 . Below T 0 , 1/ T 1 shows a gaplike decrease with a gap magnitude of 106 K, being consistent with the macroscopic measurements. The Korringa term below 10 K after the gaplike decrease suggests a gap opening over a portion of the Fermi surface.