Microwave electrodynamics of the antiferromagnetic superconductor GdBa2Cu3O7-delta.

The temperature dependence of the microwave surface impedance and conductiv ity are used to study the pairing symmetry and properties of cuprate superc onductors. However, the superconducting properties can be hidden by the eff ects of paramagnetism and antiferromagnetic long-range order in the cuprate s. To address this issue we have investigated the microwave electrodynamics of GdBa2Cu3O7-delta, it rare-earth cuprate superconductor which shows long -range ordered antiferromagnetism below T-N=2.2 K, the Neel temperature of the Gd ion subsystem. We measured the temperature dependence of the surface resistance and surface reactance of c-axis oriented epitaxial thin films a t 10.4, 14.7 and 17.9 GHz with the parallel plate resonator technique down to 1.4 K. Both the resistance and the reactance data show an unusual upturn at low temperature and the resistance presents a strong peak around TN mai nly due to change in magnetic permeability.