Ornstein-Zernike expression for correlation functions near a tricritical point

We calculate the Fourier transform of the spin-spin correlation function of a metamagnet (a simple-cubic array of Ising spins 1/2 with ferromagnetic planes coupled antiferromagnetically) in the Ornstein-Zernike (OZ) approximation. We evaluate this expression near $\lambda$ points and at the tricritical point. The divergence of the staggered susceptibility is found to have the usual OZ form near $\lambda$ and tricritical points. The uniform susceptibility diverges as the tricritical point is approached from the ordered phase, but the nature of the divergence differs radically from the usual OZ form. We also present and compare the correlation functions of the Blume-Emery-Griffiths (BEG) model with those of the metamagnet to find a complete isomorphism between them.