MAGNETIC MODELS OF NONSTOICHIOMETRIC HIGH-TEMPERATURE SUPERCONDUCTORS

Valence charge fluctuations on copper in high-temperature superconduct ors can only give a spin-1/2 system when copper is in the charge state Cu2+. As charge on the copper fluctuates because of lattice stoichiom etry in turn related to the concentration of oxygen atoms. so the conc entration of spin-1/2 atoms varies. This is modelled with the magnetic interaction topology varying from being cubic to rectangular planar. In all cases various magnetic properties especially the magnetic trans ition temperature and susceptibility are calculated. It is suggested t hat the observed magnetic behaviour of oxygen deficient high-temperatu re superconducting materials may be interpreted within such a magnetic model, with the magnetic interaction between adjacent superconducting layers varying with oxygen stoichiometry.