For ferrofluids that are described by a system of hard spheres interacting via dipolar forces we evaluate the magnetization as a function of the internal magnetic field with a Born-Mayer technique and an expansion in the dipolar coupling strength. Two different approximations are presented for the magnetization, considering different contributions to a series expansion in terms of the volume fraction of the particles and the dipolar coupling strength.

• Received 11 May 2000

DOI:https://doi.org/10.1103/PhysRevE.62.6875