Observation of an Unusual Magnetic Anomaly in the Superconducting Mixed State of Heavy-Fermion Compound UBe_(13) by Precise dc Magnetization Measurements

摘要

We have performed precise dc magnetization measurements for a single crystal of Ube_(13) 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 Ube_(13) has a magnetically unusual SC state. We studied the magnetization curves of Ube_(13), 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.