SINGLET-TRIPLET MODEL OF CUPRATE MAGNETISM

A model for describing the spin subsystem of cuprates within a model o f polar singlet-triplet Jahn-Teller centers is proposed. In this model spin ordering is described by two vector order parameters S (the tota l spin of a CuO4 cluster) and V (the operator of the change in spin mu ltiplicity per cluster). It is shown within a modified mean-field appr oximation that the formation of a noncollinear magnetic structure char acterized by an antiferromagnetic wave vector, which, however, has a n ontrivial temperature dependence of the order parameters, is possible along with the formation of ordinary collinear structures of the (anti )ferromagnetic type. The temperature dependences of the order paramete rs and the principal equilibrium thermodynamic characteristics, viz., the static susceptibility and the specific heat, are obtained. (C) 199 8 American Institute of Physics. [S1063-7834(98)00410-9].