Paramagnetic resonance of Gd3+ions in the high-Tcsuperconductor Y1Ba2Cu3Ox

The EPR spectrum of Gd3+ ions diluted (0.5% and 0.1%) in powdered samples of the high-Tc(Tc-92 K) superconductor Y1Ba2Cu3Ox has been measured at X-band in the temperature range 4.2-300 K. It was shown that the EPR spectrum exhibits significant changes in g-shift, thermal broadening and intensity well below Tc. The results are analysed in terms of existing theoretical models.