Magnetic anisotropy and thermodynamic anomaly in the superconducting mixed state of UBe13 probed by static dc magnetization measurements

Abstract

Static dc magnetization M(H) measurements were performed for a single crystal of UBe13 down to 0.1 K in magnetic fields up to 80 kOe for H∥〈100〉 and H∥〈110〉. For both field directions, an unusual magnetic anomaly was observed at HMag*∼20–30 kOe in the superconducting mixed state. This anomaly was seen in the thermal-equilibrium-magnetization curves as well as the increasing- and decreasing-field processes of the raw magnetization curves, implying a change of the thermodynamic property at HMag*. Furthermore, the magnetic anisotropy of the superconducting diamagnetic response is found to be significant above HMag*, possibly associated with the anisotropy of the upper critical field Hc2. Considering the suppression of reduced upper critical field h* and the dramatic decrease of Maki parameter κ2 around 0.9Tc, the paramagnetic effect is present in UBe13. The paramagnetic effect in UBe13 could become anisotropic at low temperature below ∼Tc/2. An alternative explanation of the magnetic anisotropy is however that the anisotropy of the nonlinear susceptibility for the heavy electrons in the vortex cores becomes significant below ∼Tc/2.

Source-reported materials — not catalogue approval

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