Detection of Tc in YBa2Cu3O7 single crystals by E.S.R. ; identification of the magnetic centers

Abstract

We show that the ESR spectrum detected in YBa 2 Cu 3 O 7 single crystals, although anisotropic, is not intrinsic but due to oriented crystallites of the green phase Y 2 BaCuO 5 . The intensity of ESR strongly reduces below T c , probably reflecting the local attenuation of the rf field. The absence of ESR from the intrinsic Cu 2+ ions probably indicates strong antiferromagnetic coupling. No skin effect is observed at 10 GHz and 300 K, contrary to the predictions of the usual theory of normal skin depth in metals.