Magnetization of concentrated polydisperse ferrofluids: cluster expansion.

The equilibrium magnetization of concentrated ferrofluids described by a system of polydisperse dipolar hard spheres is calculated as a function of the internal magnetic field using the Born-Mayer or cluster expansion technique. This paper extends the results of Huke and Lücke [Phys. Rev. E 62, 6875 (2000)] obtained for monodisperse ferrofluids. The magnetization is given as a power series expansion in two parameters related to the volume fraction and the coupling strength of the dipolar interaction, respectively.