Fluctuation-induced first-order transition in a bcc Ising model with competing interactions

We study the simple system of ($S=\frac{1}{2}$) Ising spins on a bcc lattice with ferromagnetic nearest-neighbor and antiferromagnetic next-nearest-neighbor exchange. Particular emphasis is placed on the region of competition between ferromagnetic and antiferromagnetic ordering of the second kind [AF(2)]. Renormalization-group $\epsilon$-expansion methods along with Monte Carlo analysis leads to the suggestion that the mean-field bicritical phase diagram becomes, with the inclusion of fluctuations, a critical-end-point diagram.