  A method of integral equations is developed to study inhomogeneous fluids
with planar spins in an external field. As a result, the calculations for these
systems appear to be no more difficult than those for ordinary homogeneous
liquids. The approach proposed is applied to the ferromagnetic XY spin fluid in
a magnetic field using a soft mean spherical closure and the Born-Green-Yvon
equation. This provides an accurate reproduction of the complicated phase
diagram behavior obtained by cumbersome Gibbs ensemble simulation and multiple
histogram reweighting techniques.
