DC magnetization of YbIr2Zn20 was measured in magnetic fields H (|| ) up to 14.5 T at low temperatures down to 0.09 K, focusing attention on the metamagnetic behavior. At the base temperature of T = 0.09 K, three sharp structures were observed in the differential susceptibility dM/dH at 6.2, 9.7 and 11.2 T, with the peak at 9.7 T being the largest. The amplitudes of these anomalies are strongly T dependent and those at 6.2 and 11.2 T disappear above 0.7 and 0.4 K, respectively. The peak value of dM/d H of the main peak at 9.7 T exhibits an unusual temperature variation on cooling below 1 K, with a divergent tendency persisting towards the lowest temperature. This feature is different from what one would expect for the normal Fermi liquid systems, and suggests the existence of underlying quantum critical behavior. The results are discussed in relation to the recently proposed field-induced valence crossover scenario.
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