5,396 research outputs found
Magnetophoresis of nonmagnetic particles in ferrofluids
Ferrofluids containing nonmagnetic particles are called inverse ferrofluids.
On the basis of the Ewald-Kornfeld formulation and the Maxwell-Garnett theory,
we theoretically investigate the magnetophoretic force exerting on the
nonmagnetic particles in inverse ferrofluids due to the presence of a
nonuniform magnetic field, by taking into account the structural transition and
long-range interaction. We numerically demonstrate that the force can be
adjusted by choosing appropriate lattices, volume fractions, geometric shapes,
and conductivities of the nonmagnetic particles, as well as frequencies of
external magnetic fields.Comment: 24 pages, 7 figure
Photonic Hall Effect in ferrofluids: Theory and Experiments
An experimental and theoretical study on the Photonic Hall Effect (PHE) in
liquid and gelled samples of ferrofluids is presented. The ferrofluids are
aqueous colloidal suspensions of Fe(_{2})CoO(_{4}) particles, which can be
considered as anisotropic and absorbing Rayleigh scatterers.
The PHE is found to be produced by the orientation of the magnetic moments of
the particles, as is also the case for the Faraday effect. The dependence of
the PHE with respect to the concentration of the scatterers, the magnetic field
and the polarization of the incident light is measured in liquid and in gelled
samples and is compared to a simple model based on the use of a scattering
matrix and the single scattering approximation.Comment: 20 pages, 11 figures, submitte
Magnetic properties of colloidal suspensions of interacting magnetic particles
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: ({\em i}) the magnetization with
the initial magnetic susceptibility as a special case and ({\em 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.Comment: Review. 62 pages, 4 figure
Magnetization of polydisperse colloidal ferrofluids: Effect of magnetostriction
We exploit magnetostriction in polydisperse ferrofluids in order to generate
nonlinear responses, and apply a thermodynamical method to derive the desired
nonlinear magnetic susceptibility. For an ideal gas, this method has been
demonstrated to be in excellent agreement with a statistical method. In the
presence of a sinusoidal ac magnetic field, the magnetization of the
polydisperse ferrofluid contains higher-order harmonics, which can be extracted
analytically by using a perturbation approach. We find that the harmonics are
sensitive to the particle distribution and the degree of field-induced
anisotropy of the system. In addition, we find that the magnetization is higher
in the polydisperse system than in the monodisperse one, as also found by a
recent Monte Carlo simulation. Thus, it seems possible to detect the size
distribution in a polydisperse ferrofluid by measuring the harmonics of the
magnetization under the influence of magnetostriction.Comment: 23 pages, 4 figures. To be accepted for publication in Phys. Rev.
Polygonal micro-whirlpools induced in ferrofluids
We report on the observation of the polygonal whirlpools in the thin layer of
ferrofluid under illumination with a laser beam carrying optical vortex and in
the presence of a vertical magnetic field. This kind of structures have
attracted attention after discovering a hexagonal storm in Saturns atmosphere.
Our polygonal whirlpools were created in a closed system (no free surfaces) in
micro scale (whirlpool diameter less than 20 micrometers) by the use of
holographic optical tweezers. The polygonal shape was changed by varying the
magnetic field strength or value of the optical vortex topological charge
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