The effect of an external magnetic field on the gas-liquid transition in   the Heisenberg spin fluid
  We present the theoretical phase diagrams of the classical Heisenberg fluid in an external magnetic field. A consistent account of correlations is carried out by the integral equation method. A nonmonotoneous effect of fields on the temperature of the gas-liquid critical point is found. Within the mean spherical approximation this nonmonotoneous behavior disappears for short-range enough spin-spin interactions. 
T.G.Sokolovska, R.O.Sokolovskii