Recently, there has been a renewed interest in the layered hexagonal antiferromagnet FeBr$_2$.[@dea95; @sel95; @sel96; @aru96; @kat97; @ple97; @hel97; @pet97; @pet98] In the ordered phase of FeBr$_2$ the spins of the iron ions are aligned ferromagnetically in the triangular layers, the layers being stacked antiferromagnetically along the $c$–axis. Adjacent iron layers are separated by two nonmagnetic bromide planes.

Investigations of de Azevedo et al. [@dea95] revealed noncritical anomalies in the antiferromagnetic phase of FeBr$_2$ below the transition line to the paramagnetic phase, e.g. maxima or shoulders in the temperature derivatives of the magnetization at constant axial fields. The ingredients crucial for the existence of these noncritical spin fluctuations are the effectively weak ferromagnetic intralayer couplings and the large number of interlayer nearest neighbors (due to the superexchange mediated by the bromide planes).[@sel95; @sel96; @ple97]

Surprisingly, measurements of the magnetic specific heat [@aru96] revealed a sharp peak superposed on a broad shoulder or maximum below the transition to the paramagnetic phase, in contrast to Monte Carlo simulations of Ising metamagnets [@sel95; @sel96; @aru96; @ple97] showing only a noncritical shoulder or maximum. The peculiar shape of the specific heat of FeBr$_2$ was tentatively interpreted [@aru96; @kat97] as the signature of a new 