ESR and magnetic susceptibility of localized cu magnetic moments in YBco-ceramics

The temperature dependences of the Cu 2+ ESR signal intensity in YBa 2 Cu 3 O x samples with different oxygen stoichiometry (6.21 ≤ x ≤ 6.93) and in a Y 2 BaCuO 5 sample ("green phase") as well as the temperature dependences of dc magnetic susceptibility have been measured. The paramagnetic susceptibilities of YBa 2 Cu 3 O x and Y 2 BaCuO 5 determined by ESR technique and by dc magnetic susceptibility measurements are found to be characterized by different Curie-Weiss temperatures. The conclusion has been reached that the observed in YBa 2 Cu 3 O x Cu 2+ ESR signal is intrinsic and is not connected with the impurity phase Y 2 BaCuO 5 . The weak Cu 2+ ESR signal observed in the orthorhombic superconducting samples (x > 6.5) is related to the presence of tetragonal regions with a decreasing oxygen content.