  Motivated by recent experiments on the metamagnet FeBr2, anomalies of the
magnetization and the specific heat in the antiferromagnetic phase of related
spin models are studied systematically using Monte Carlo simulations. In
particular, the dependence of the anomalous behavior on competing intralayer
interactions, the spin value and the Ising-like anisotropy of the Hamiltonian
is investigated. Results are compared to experimental findings on FeBr2.
