Persistent supercurrents in MgB2

Persistent currents were induced in rings of superconducting granular MgB2. We measured the magnetic self-fields generated by these currents using a scanning Hall probe. We obtained both the temperature dependence of the persistent current at the critical level between 15 K and Tc (39 K) and the time decay of the persistent current for up to 105 s. The time decay for this time interval is less than 1% at temperatures between 15 and 35 K. This rate is much smaller than that observed in high critical current rings of YBCO thin films, which is about 10% at 15 K.