Possible Long-Range Order with Singlet Ground State in CeRu2Al10

Abstract

We investigate the thermal and transport properties of Ce x La 1- x Ru 2 Al 10 to clarify the origin of the recently discovered mysterious phase below T 0 =27 K in CeRu 2 Al 10 where a large magnetic entropy is released, however, the existence of an internal magnetic field is ruled out by 27 Al-NQR measurement. We find that T 0 decreases with decreasing x and disappears at x ∼0.45. T 0 of CeRu 2 Al 10 is suppressed down to 26 K under H =14.5 T along the a -axis. These results clearly indicate that the transition has a magnetic origin and is ascribed to the interaction between Ce ions. Considering the results of specific heat, magnetic susceptibility, thermal expansion, and electrical resistivity and also 27 Al-NQR, we propose that the transition originates from the singlet pair formation between Ce ions. Although its properties in a Ce dilute region is basically understood by the impurity Kondo effect, CeRu 2 Al 10 shows a Kondo-semiconductor-like behavior. The phase transition at T 0 may be characterized as a new type of phase transition that appears during the crossover from the dilute Kondo to the Kondo semiconductor.