title: Linear and nonlinear magnetic properties of ferrofluids.
abstract: Within a high-magnetic-field approximation, employing Ruelle's algebraic perturbation theory, a field-dependent free-energy expression is proposed which allows one to determine the magnetic properties of ferrofluids modeled as dipolar hard-sphere systems. We compare the ensuing magnetization curves, following from this free energy, with those obtained by Ivanov and Kuznetsova [Phys. Rev. E 64, 041405 (2001)] as well as with new corresponding Monte Carlo simulation data. Based on the power-series expansion of the magnetization, a closed expression for the magnetization is also proposed, which is a high-density extension of the corresponding equation of Ivanov and Kuznetsova. From both magnetization equations the zero-field susceptibility expression due to Tani et al. [Mol. Phys. 48, 863 (1983)] can be obtained, which is in good agreement with our MC simulation results. From the closed expression for the magnetization the second-order nonlinear magnetic susceptibility is also derived, which shows fair agreement with the corresponding MC simulation data.
authors.affiliation: Institute of Physics and Mechatronics, University of Pannonia, 8200 Veszprém, Hungary.
authors.forename: I
authors.initials: I
authors.lastname: Szalai
authors.affiliation: Institute of Mechanics and Mechatronics, The University of West Hungary, H-9401 Sopron, P. O. Box 132, Hungary.
authors.forename: S
authors.initials: S
authors.lastname: Nagy
authors.affiliation: Max-Planck-Institut für Intelligente Systeme, Heisenbergstr. 3, D-70569 Stuttgart, Germany.|IV. Institut für Theoretische Physik, Universität Stuttgart, Pfaffenwaldring 57, D-70569 Stuttgart, Germany.
authors.forename: S
authors.initials: S
authors.lastname: Dietrich