mu SR study of a mixed compound NiC2O4 2 center dot(2-methylimidazole)(x)(H2O)(1-x)

We examined the muon spin relaxation (mu SR) of mixed compounds NiC2O4 2 . (2-methylimidazole)(x)(H2O)(1-x) with x = 1.0 and 0.49. Although the macros copic magnetic properties are obviously different from each other, both sys tems exhibit similar behavior in the muon spin relaxation. In addition, in the x = 0.49 (SG) sample, a critical slowing down of spin dynamics was not observed in this mu SR measurement, though the spin-glass like freezing was observed in the susceptibility measurements. Qualitative explanation of th ese anomalous observations is given.