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 new route of fluorination by NH4HF2 and its superconducting phase is investigated by electron paramagnetic resonance, direct microwave absorption and non-resonant response employing magnetic field modulated microwave absorption. These studies have given clear evidence for the occurrence 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 with F-19 super hyperfine structure due to interaction with two equivalent 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 increased in the superconducting phase smearing out the F-19 shfs below 35 K. This is consistent with what is normally expected in superconductors.