EPR measurements at room temperature (RT) on the oxygen deficient (La, Tm)-Ba-Cu-O compound (tetragonal phase) revealed a line centered at g=2.895(5) with linewidth ΔH=0.015(1)T. The line is ascribed to Tm2+ ions (4f13, 2F7/2) assuming that the Γ(7) doublet is the ground state. A characteristic EPR spectrum of divalent copper ions was also observed. © 1992.

Electron paramagnetic resonance obtained from the tetragonal RBa2Cu3O6+x (R ≡ Nd, Sm, Tm) compounds exhibit a well defined line resulting from coupled divalent Cu ions. Below 20 K the g parameter of this signal is strongly temperature dependent. At about the same temperatures there is a ferromagnetic-like transition in the magnetic susceptibility. © 1992 Taylor & Francis Ltd.

EPR spectra between 9.7 K and room temperature (RT) were taken for EuBa2Cu3O7-δ in tetragonal and orthorhombic phases. Our results indicate significant differences between the EPR spectra of Cu2+ ions in the tetragonal and orthorhombic phase. It is concluded that in the tetragonal phase, the Cu2+ complex has axial symmetry. Furthermore, at low temperatures the observed EPR signal is associated with superexchange interaction between Eu2+ ions across oxygen bridges. © 1991.

The EPR spectra of perovskite ceramics of Gd0.5RE0.5Ba2Cu3O7−δ type (RE  La, Pr, Nd, Sm, Eu, Dy, Ho, Y, Er, Tm, Yb, and Lu) in tetragonal (non‐HTC) phase are investigated as a function of temperature in the range 40 to 3 K. A signal arising from the isotropic exchange interaction of coupled pairs of Cu2+ ions is detected. The intensity of this signal is strongly dependent on the RE ions and its g‐factor varies with temperature. Magnetic measurements show the existence of ferromagnetic anomalies at these low temperature. In the orthorhombic phase, these materials exhibit a superconducting phase transition in the range of 85 to 95 K, apart from the samples with La ions where a TC ≈ 69 K is found and the samples with Prions where a superconducting state can not be observed. Copyright © 1992 WILEY‐VCH Verlag GmbH & Co. KGaA

The EPR spectra of polycrystalline oxygenated and non-oxygenated (large oxygen deficiency) LaBa2Cu3O7- delta compounds, obtained at various temperatures, were studied and analysed. The oxygenated samples showed a transition temperature Tc at about 50 K. The EPR spectrum of the Cu2+ ions in the orthorhombic local symmetry was observed. It was found that these spectra are essentially influenced by an oxygen deficiency and thermal treatment. In the non-oxygenated samples, at a certain stage of the annealing process an EPR spectrum was detected at low temperatures. After the final anneal, this EPR spectrum showed significant changes. Changes were also observed in the corresponding XRD spectra indicating reductions in the concentrations of the CuO and BaCuO2 impurity phases. Additionally, the EPR spectrum of divalent copper ions in the axial local symmetry in the dx2-y2 ground state was observed.

EPR, XRD, and magnetic studies are presented for Pr0.5Re0.5Ba2Cu3O7-δ compounds (Re= La, Nd, Sm, Eu, Gd, Dy, Ho, Y, Er, Tm, Yb, and Lu) in the orthorhombic and tetragonal (large oxygen deficiency) phase. For the samples with Re=Dy, Ho, Y, Er, Tm, Yb, and Lu in the orthorhombic phase, the transition to the superconducting state has been observed in the temperatures range Tc between 18 and 40 K. For the samples with Nd and Yb in the tetragonal phase, EPR spectra coming from trivalent rare earth ions have been recorded. In the nonoxygenated sample Pr0.5La0.5Ba2Cu3O7-δ the EPR spectrum arising from the non-Kramers trivalent praseodymium ion has been observed. A broad EPR line appearing in all our samples was attributed to superexchange interaction between copper ions over oxygen (O2-) bridges. Interestingly, for the Pr0.5Re0.5Ba0.5Cu3O7-δ (Re = Er and Lu) compounds in the tetragonal phase at liquid-nitrogen temperature, a nonresonant microwave absorption in low magnetic fields has been detected. © 1992 Plenum Publishing Corporation.