Magnetic properties of colloidal suspensions of interacting magnetic particles

Abstract

We review equilibrium thermodynamic properties of systems of magnetic particles like ferrofluids in which dipolar interactions play an important role. The review is focussed on two subjects: (i) the magnetization with the initial magnetic susceptibility as a special case and (ii) the phase transition behavior. Here the condensation ("gas/liquid") transition in the subsystem of the suspended particles is treated as well as the isotropic/ferromagnetic transition to a state with spontaneously generated long-range magnetic order.

Structural control of elastic moduli in ferrogels and the importance of non-affine deformations

“…They consist of superparamagnetic or ferromagnetic particles of nano-or micrometer size embedded in a crosslinked polymer matrix [6]. In this way, they combine the properties of ferrofluids and magnetorheological fluids [7][8][9][10][11][12][13][14][15][16] with those of conventional polymers and rubbers [17]: we obtain elastic solids, the shape and mechanical properties of which can be changed reversibly from outside by applying external magnetic fields [6,[18][19][20][21][22][23][24][25].…”

Liquid-gas phase behavior of Stockmayer fluid with high dipolar moment

“…Stockmayer fluid is a simple and convenient model, which is often used to study the properties of the polar fluids [1] and ferrofluids [2][3][4], in particular their phase behavior. Perhaps first theoretical predictions for the liquid-gas phase diagram of Stockmayer fluid was given by Stell, Rasaiah and Narang (SRN) [5,6].…”

The magneto-optical behaviors modulated by unaggregated system for γ-Fe2O3–ZnFe2O4 binary ferrofluids

“…Therefore, ferrofluids are typical dipolar fluids; 1 in any case, the magnetic particles cause the ferrofluids to display the equilibrium thermodynamics of a paramagnetic liquid. 2 It is well established that ferrofluids exhibit magneto-optical effects such as Faraday rotation, Faraday ellipticity, birefringence, and dichroism. However, the study of magneto-optical effects is not the only area of interest, since the microstructure of ferrofluids, and particle interactions, may also be seen at lower particle volume fractions than those used in magnetization measurements.…”

“…3 The magneto-optical effects are believed to result from chain-like aggregates produced by interparticle interactions. 4 The magnetic particles interact pairwise with each other via the dipole-dipole interaction potential U d-d , 2 which can be described as where μ r is the relative magnetic permeability in the magnetic medium, and is taken as unity in a magnetically neutral medium, μ 0 is the vacuum permeability, r ij is the displacement vector of the particles i and j, and p mi , p mj are the point dipole moments fixed inside these particles. Under the influence of an external magnetic field, the increased orientation of the magnetic moments of the ferroparticles leads to an increase in the effective attraction between them.…”

“…Under the influence of an external magnetic field, the increased orientation of the magnetic moments of the ferroparticles leads to an increase in the effective attraction between them. 5 The maximum magnetic interaction potential U d-d,max between the dipole moments connected head to tail is U d-d,max = −μ r p mi p mj /2πμ 0 d ij 3 (2) where d i j = (d i + d j )/2, and d i and d j are the diameters of the particles i and j, respectively. For a ferrofluid, the dipolar coupling constant λ is an important parameter to characterize the system in a magnetically neutral medium (μ r = 1), and is written as…”