Magnetic field dependence of microwave absorption in the superconducting Y(123), Bi(2223) and Tl(2122) compounds

This paper reports on direct microwave absorption at x-bank in superconducting single phase Y-123, Bi-2223 and Tl-2122 compounds that was investigated as a function of magnetic field (0 to 10 kG) and temperature (20 K to Tc). At each of the temperatures the samples were zero-field cooled and microwave absorption was investigated with increasing field at increments of 100 mG up to 10 G and at larger increments at higher fields. The important findings are: The microwave absorption starts at 20K from a field of 3 G which shifts to lower fields with increasing temperature. This demonstrates the importance of zero-field cooling at each of the temperatures. The magnetic field dependence of microwave absorption consists of two parts, one at lower other at higher fields presumably due to flux on the lattice in the superconducting grains. It is shown that the absorption due to weak links does not increase exponentially with field, as reported in the literature, but shows a distinct peaking