Abstract
EPR is .one of the main methods used to study the structure of copper complexes in various materials. A number of EPR studies of high-Tc compounds of the R123 type has appeared in which magnetic resonance lines were attributed to copper ions or copper complexes [1]. Despite a vast amount of literature the nature of EPR centers has not yet been definitively clarified. The main feature of the EPR spectrum is usually a single line with g=2.0-2.4 which depending on the sample preparation is observed at high or low (T<50 K) temperatures. This signal is attributed to isolated Cu2+ ions in the chain fragments [2] or to copper-oxygen clusters with S=2 and an initial nonmagnetic splitting between the singlet <0> and doublet <±l>states [3]. Another EPR line at g=4.2 has often been reported and its origin is still controversial. Various models of this center have been advanced ranging from the pairs of Cu2+ ions with weak exchange interaction [4], Cu3+ (S=l) ions [5], pairs of oxygen holes localized at apical oxygens [6], Cu2+ - Cu4+ pairs [7] to the chain fragments of copper ions of variable valence with S=0 ground state and S=l excited state [8]. Yet another metastable copper-oxygen clusters with spins S=3/2, 5/2, and 7/2 corresponding to resonance lines in weak magnetic fields have been observed and identified [9].
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Likodimos, V., Guskos, N., Typek, J., Wabia, M. (2002). High Spin Paramagnetic Centers in Tetragonal Phase of Er123, Dy123, and (Er,Y)123 Compounds. In: Annett, J.F., Kruchinin, S. (eds) New Trends in Superconductivity. NATO Science Series, vol 67. Springer, Dordrecht. https://doi.org/10.1007/978-94-010-0544-9_17
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DOI: https://doi.org/10.1007/978-94-010-0544-9_17
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