Polycrystalline MgB2, synthesized using conventional solid-state reaction, was investigated for its magnetic field-dependent microwave absorption by using a standard X-band electron paramagnetic resonance spectrometer. The changes in microwave absorption as a function of temperature and/or magnetic field were recorded by following the microwave reflectivity of a sample-loaded cavity. The modulated low-field microwave absorption signal was found to be similar to that observed in high-temperature superconducting materials. The field dependent direct microwave absorption in the 0 to 10kG range was used to determine HC1 values at different temperatures, and the value of HC1(0) was found to be 250G. The absorbed microwave power was found to obey a H½ dependence with a change of slope; indicating a transition from a strongly pinned flux lattice to a flux flow regime.

Magnetic Field Dependent Microwave Absorption Studies on a MgB2 Superconductor. M.K.Bhide, R.M.Kadam, M.D.Sastry, A.Singh, S.Sen, D.K.Aswal, S.K.Gupta, V.C.Sahni: Superconductor Science and Technology, 2001, 14, 572-5