Ising-Model "Metamagnet" and Tricritical Susceptibility Exponent

A spin-½ Ising-model "metamagnet" is studied by the method of high-temperature expansions. The phase boundary in the $H-T$ plane is obtained for a simple cubic lattic with in-plane ferromagnetic interactions but between-plane antiferromagnetic coupling, and a tricritical point is located. Along the critical line, the staggered susceptibility appears to have an exponent $\frac{5}{4}$ (consistent with the universality hypothesis), while at the tricritical point, the direct susceptibility shows a tricritical exponent of ½.