Magnetization study of the heavy fermion superconductor PrOs4Sb12

Abstract We have carefully measured the DC magnetization of a high-quality single crystal of PrOs 4 Sb 12 down to 60 mK with a special interest in the superconducting phase. The temperature dependence of the magnetization M ( T ) at 100 Oe exhibits two distinct anomalies at T c 1 =1.83 K and T c 2 =1.65 K , in good agreement with the specific heat measurements at zero field. Increasing magnetic field H , both T c1 ( H ) and T c2 ( H ) move toward lower temperatures without showing a tendency of intersecting to each other. Above 10 kOe , the transition at T c2 ( H ) appears to merge into a line of the peak effect which is observed near the upper critical field H c2 in the isothermal M ( H ) curves, suggesting a common origin for these two phenomena.