MICROWAVE-ABSORPTION AND EPR STUDIES OF A NEW COPPER OXYFLUORIDE SUPERCONDUCTOR SYNTHESIZED THROUGH THE AMMONIUM BIFLUORIDE ROUTE

The recently reported superconductor Sr2CuO2F2.4 is synthesised by a n ew route of fluorination by NH4HF2 and its superconducting phase is in vestigated by electron paramagnetic resonance, direct microwave absorp tion and non-resonant response employing magnetic field modulated micr owave absorption. These studies have given clear evidence for the occu rrence of a superconducting phase below 40 K. From the magnetic field dependence of the changes in microwave absorption, the lower critical field H-c1 (perpendicular to the c-axis) is determined to be 100 G at 10 K. The EPR studies on this oxyfluoride have shown a Cu2+ Signal wit h F-19 super hyperfine structure due to interaction with two equivalen t F nuclei. In view of its low intensity it was assigned to a possible 'defect site' in the lattice. The line width of the EPR signal increa sed in the superconducting phase smearing out the F-19 shfs below 35 K . This is consistent with what is normally expected in superconductors .