EPR study of some rare-earth ions (Dy3+, Tb3+ and Nd3+) in YBa2Cu3O6   compound
  We investigate the low temperature X-band electron paramagnetic resonance (EPR) of YBa2Cu3O6 compounds with x = 6.0 doped with Dy3+, Tb3+, and Nd3+. The EPR spectra of Dy3+ and Tb3+ have been identified. The EPR of Tb3+ is used also to study the effect of suppression of high Tc superconductivity. The EPR of Nd3+ is probably masked by the intense resonance of Cu2+. All experimental EPR results compare well with theoretical estimations. 
M.R. Gafurov,, V.A. Ivanshin, I.N. Kurkin, M.P. Rodionova, H. Keller,   M. Gutmann, U. Staub