A Spin-Spin Interaction Model of Disordered Octahedra in Superconducting Bismuthate

Spin-spin interaction induced magnetization and susceptibility contributed by spins of the BiO6 octahedra in bismuthates have been calculated. Different disordered forms of exchange integral have been used with the help of a set of parameters in a model form. Using spins of Bi $\left (|\vec {S}|=\frac {3}{2}\right )$ and O $\left (|\vec {S}|=1\right )$ , we have calculated the magnetization and susceptibility numerically within the framework of the mean field theory (MFT). Low upper critical fields in bismuthates and the saturation spin dipole moment of the octahedra are related. The variation of the susceptibility with T exhibits a peak at a temperature Tm. An upturn in the experimental susceptibility as a function of T in the normal state has been explained by our numerical results.