Effect of DPPH radical adsorption on the superconducting properties of HTSC bismuth ceramics

Measuring the AC susceptibility and registering the ESR spectra of the stable 1,1-diphenyl-2-picryl-hydrazyl (DPPH) radical at 77.4–125 K, we have studied the effect of the radical on the current properties of the intergranular contacts in the superconducting ceramics Bi1.8Pb0.3Sr1.9Ca2.8Cu3.4Oy. Critical current in the ceramics is decreased by the magnetic field generated by the radical spin. The effect of the field on the critical current corresponds to the location of the adsorbed radical at a distance of 56 Å from the superconducting phase.