Anomalous magnetic hysteresis in the microwave surface resistance of MgB2 superconductor

摘要

We report experimental results of the field-induced variations of themicrowave surface resistance in samples of MgB2, produced by different methods.By sweeping the DC magnetic field at increasing and decreasing values, we havedetected a magnetic hysteresis that can be ascribed to the different magneticinduction, due to the critical state of the fluxon lattice. The hysteresisobserved in the bulk samples has an unusual shape, which cannot be justified inthe framework of the critical-state models.