Based on numerical results of dynamic susceptibility, a simple theory of the dynamic response of a ferrofluid to an ac magnetic field is obtained that includes both the effects of interparticle dipole-dipole interactions and the dependence on field amplitude. Interparticle interactions are incorporated in the theory using the so-called modified mean-field approach. The new theory has the following important characteristics: in the noninteracting regime at a weak ac field, it gives the correct single-particle Debye theory results; it expands the applicability of known theories valid for high concentrations [Ivanov, Zverev, and Kantorovich, Soft Matter 12, 3507 (2016)] or large values of ac field amplitudes [Yoshida and Enpuku, Jpn. J. Appl. Phys. 48, 127002 (2009)], in accordance with their applicability. The susceptibility spectra are analyzed in detail. It is demonstrated that interparticle dipole-dipole interactions and an increase in field amplitude have an opposite effect on the dynamic response of ferrofluids, so that at certain field amplitudes, relaxation processes in the system of interacting particles are determined by the characteristic relaxation times for an ideal paramagnetic gas. The new theory correctly predicts the dynamic susceptibility and characteristic relaxation times of a ferrofluid at high ac field amplitudes as long as the Langevin susceptibility ${\ensuremath{\chi}}_{L}\ensuremath{\lesssim}1$, which is a complex characteristic of ferrofluid density and the intensity of interparticle dipole-dipole interactions.

Dynamic magnetic susceptibility of a ferrofluid: The influence of interparticle interactions and ac field amplitude.

Reconfiguring nanostructures in magnetic fluids using pH and magnetic stimulus for tuning optical properties

Synthesis and magneto-structural properties of chitosan coated ultrafine cobalt ferrite nanoparticles for magnetic fluid hyperthermia in viscous medium

The response of ferrofluids to a high-amplitude AC magnetic field is important for several applications including magnetic hyperthermia and biodetection. In computer simulations of the dynamic susceptibility of a ferrofluid outside the linear response region, there are several problems associated with the fact that an increase in the frequency of the AC field leads to the appearance of additional computational errors, which can even lead to unphysical results. In this article, we study the dependence of the computational error arising in the computer simulation of the dynamic susceptibility on the input parameters of the numerical algorithm: the length of the time step, the total number of computer simulation periods, and averaging period. Computer simulation is carried out using the Langevin dynamics method and takes Brownian rotational relaxation of magnetic particles and interparticle interactions into account. The reference theory [Yoshida T.; Enpuku K. Jap. J. Ap. Phys. 2009] is used to estimate computational error. As a result, we give practical recommendations for choosing the optimal input parameters of the numerical algorithm, which make it possible to obtain reliable results of the dynamic susceptibility of a ferrofluid in a high-amplitude AC field in a wide frequency range.

Computer simulations of dynamic response of ferrofluids on an alternating magnetic field with high amplitude

Numerical Simulation and Experimental Study on the Ferrofluid Second-order Buoyancy with a Free Surface

Magnetic hyperthermia studies in magnetite ferrofluids based on bio-friendly oils extracted from Calophyllum inophyllum, Brassica juncea, Ricinus communis and Madhuca longifolia

M. S. Gopika

Papers

Magnetic hyperthermia studies in magnetite ferrofluids based on bio-friendly oils extracted from Calophyllum inophyllum, Brassica juncea, Ricinus communis and Madhuca longifolia