NITROXYL RADICAL ADSORPTION ON SUPERCONDUCTING YTTRIUM CERAMICS INCREASES ITS CRITICAL-CURRENT

It has been found experimentally that paramagnetic materials like the stable nitroxyl radical (TEMPO) greatly influence the current-carrying properties of superconducting yttrium ceramics in the temperature ran ge 70.0-88.0 K. The temperature dependence of the critical current for the composite material TEMPOx-YBa2Cu3O7-delta was investigated. At so me definite concentration of nitroxyl radical in the ceramics (or valu e x) an increase of the transport critical current is shown to take pl ace. Measurements of AC magnetic susceptibility in the presence of a c onstant magnetic field as a function of temperature indicate that adso rption of nitroxyl radical only affects the value of the intergranular transport current. A hypothesis explaining the observed enhancement o f the current-carrying ability of HTSC ceramics is proposed.