Electron spin resonance with g(eff) approximate to 4.2 in YBa2Cu3O6.35. Model of chain copper-oxygen fragments

Systematic measurements are made of ESR spectra with g approximate to 4.2 i n YBa2Cu3O6+y compounds with various doping indices y. Temperature dependen ces of the spectrum intensity show that the ground states of the centers ar e singlet and the energies of the excited states M-S = +/- 1 correspond to 8-11 K. In general, the intensity of the ESR spectra varies with time and d epends on the sample preparation technology. The most probable models for t he paramagnetic centers studied are considered to be chain fragments of cop per ions of variable valence. General laws governing the energy structure o f these centers are described. (C) 2000 MAIK "Nauka/Interperiodica".