Temperature dependence of the EPR linewidth of Yb3+ ions in Y0.99Yb0.01Ba2Cu3OX (6 ≤ X ≤ 7) compounds: evidence for an anomaly near the superconducting transition

Electron paramagnetic resonance experiments on doped Yb3+ ions in Y0.99Yb0.01Ba2Cu3OX () compounds with different oxygen contents have been made. We have observed a strong temperature dependence of the EPR linewidth in all the investigated samples caused by the Raman processes of spin–lattice relaxation. The spin–lattice relaxation rate anomaly revealed near TC in the superconducting species can be assigned to the phonon density spectrum changes.