Title: MULTICRITICAL BEHAVIOUR IN MAGNETIC FLUIDS
Authors: F.Schinagl (Institute for Semiconductor Physics, Johannes Kepler University, Linz, Austria), R.Folk, H.Iro (Institute for Theoretical Physics, Johannes Kepler University, Linz, Austria)

The phases of a magnetic fluid in an external field are considered. As model systems we take an ideal (hard core) gas with Ising interaction and a van der Waals gas with additional Heisenberg interaction. In mean field approximation various phases and critical points are identified. For appropriate values of the ratio of the magnetic to the non-magnetic interactions there exist multicritical points like tricritical points and critical end points. For the ideal Ising fluid we calculate the line of wing critical points analytically and prove classical tricritical behaviour. In the van der Waals case wing critical points and the gas-liquid critical point may coexist. The corresponding phase diagrams in $\left(p,t,h\right)$-space are shown.

Comments: Figs. 2, Refs. 16, Tabs. 0.