Observation of an Unusual Magnetic Anomaly in the Superconducting Mixed State of Heavy-Fermion Compound UBe13 by Precise dc Magnetization Measurements

摘要

We have performed precise dc magnetization measurements for a single crystal of UBe13 down to 0.14 K, up to 80 kOe. We observed a magnetic anomaly in the superconducting (SC) mixed state at a field, named H*_[Mag] (～26 kOe, at 0.14 K), implying that UBe13 has a magnetically unusual SC state. We studied the magnetization curves of UBe13, assuming that the H*_[Mag] anomaly originates from (1) and unusual SC diamagnetic response, or (2) a peculiarity of the normal-state magnetization due to vortices in the SC mixed state. The origin of the H*_[Mag] anomaly is discussed.