Phase polarity in a ferrofluid monolayer of shifted-dipole spheres

Piastra, Marco; Virga, Epifanio G.

doi:10.1039/c2sm25984b

Cited by 13 publications

(15 citation statements)

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“…Piastra and Vigra 9 examined spheres located in a plane and possessing point dipoles, and they also constructed a mean-field theory for a homogeneous ferrofluid monolayer. Consistent with Piastra and Vigra, 9 the cluster size was found to increase with increased dipolar coupling. Their theory was subsequently extended by Gartland and Virga.…”

Section: Introductionsupporting

confidence: 84%

Quasi-2d fluids of dipolar superballs in an external field

Linse

2015

Soft Matter

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The structure of quasi-2d solutions of dipolar superballs in the fluid state has been determined by Metropolis Monte Carlos simulations in the absence and the presence of an external field. Superballs are 3d objects characterized by a one shape parameter. Here, superballs resembling cubes, but possessing rounded edges, have been used. Examination has been made for several magnitudes of the dipole moment in three different dipole directions. In the limit of a cube, the directions become (i) the center of mass - the center of a face (001) direction, (ii) the center of mass - the center of an edge (011) direction, and (iii) the center of mass - the corner (111) direction. At a small dipole moment, the superballs are translationally and orientationally disordered, and the dipoles become partially orientationally ordered in the presence of the field parallel to the plane of the superballs. At a large dipole moment, chains of superballs are formed, and the chains become parallel in the presence of the field. The chains remain separated for the dipole in the 001-direction and form bundles for the 011- and 111-directions. The different structures obtained for the different dipole directions are interpreted in terms of how compatible the dipole-dipole interaction is with the cube-cube interaction at short separation for the different directions of the dipole moment. Hence, the structural richness arises from an interplay of the different symmetries of a cube and of the field of a dipole.

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Section: Introductionsupporting

confidence: 84%

Quasi-2d fluids of dipolar superballs in an external field

Linse

2015

Soft Matter

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“…In order to be able to progress with an analytical formulation for the case a s 0, a second approximation is introduced by using a certain interpolation, which results in eqn (2a). This model interaction potential is shown to have good delity to the integrated average two-particle Hamiltonian; 13 we refer the reader to the original paper for details.…”

Section: Mean-field Free Energymentioning

confidence: 99%

“…Several studies are already available for the model monolayer considered here; [4][5][6] they are concerned with spatial pattern formation (chains, rings, clusters) and apply both Monte Carlo and molecular dynamics methods, mostly treating ensembles with low densities of particles. Here we pursue the avenue suggested by Piastra and Virga, 13 which proposes a mean-eld model for such a system with a goal of understanding what phases and transitions could be anticipated for a denser system of colloidal particles. In this paper, we extend that analysis in two ways.…”

Section: Introductionmentioning

confidence: 99%

“…Such a hybrid behavior results from the spontaneous magnetization predicted to arise in the plane of the layer at sufficiently low temperatures in the absence of external elds. 13 For a strong enough eld applied normal to the layer, the system loses its ability to develop transverse magnetization, and the symmetry of the response is restored with a magnetization parallel to the eld and increasing with its strength up to saturation. When the external eld is directly applied at a temperature below T c , the total magnetization remains constant as the eld strength increases (with its normal component increasing and its in-plane component decreasing) up to the point where the in-plane component is suppressed, while the normal component keeps increasing the whole while.…”

Section: Introductionmentioning

confidence: 99%

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An analytic mean-field model for the magnetic response of a ferrofluid monolayer

Gartland

Virga

2013

Soft Matter

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We extend the analysis of the mean-field model introduced in a previous paper [Piastra and Virga, Soft Matter, 2012, 8, 10969] for a monolayer of spherical colloidal particles with shifted point dipoles studied in previous work [Kantorovich et al., Soft Matter, 2011, 7, 5217]. This system was predicted to exhibit a spontaneous magnetization in the absence of any magnetic field, provided that the temperature is sufficiently low or the particles' density is sufficiently high. A ferromagnetic behavior is confirmed here by a solution in closed form for the mean-field free energy, reminiscent of (but not identical to) the classical solutions of Langevin and Weiss; the closed-form solution also applies in the presence of an external magnetic field, however oriented relative to the layer's normal. Such an analytic solution has perhaps its most telling application to the case where the external magnetic field is applied normal to the layer, where a mixed ferromagnetic and paramagnetic response is predicted. In that case, if the field's strength is not too high, then for high enough temperatures (or low enough densities) the magnetic response is paramagnetic (and with the magnetization aligned to the field), whereas for low enough temperatures (or high enough densities) an extra magnetization grows in the plane of the layer (the vertical component remaining frozen), a remnant of the ferromagnetic transition in the absence of a field. If instead the field's strength exceeds a critical value, any ferromagnetic behavior is suppressed, and the layer becomes paramagnetic at all temperatures and densities.

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“…In a recent contribution a mean-field Hamiltonian with interesting properties has been constructed for this system. 75 The paper is organized as follows: in Sec. II, we introduce the SD-particle system in detail, in Sec.…”

Section: Introductionmentioning

confidence: 99%

Microstructure and magnetic properties of magnetic fluids consisting of shifted dipole particles under the influence of an external magnetic field

Weeber

Klinkigt²,

Kantorovich³

et al. 2013

The Journal of Chemical Physics

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Articles you may be interested inTheory of magnetic fluid heating with an alternating magnetic field with temperature dependent materials properties for self-regulated heating J. Appl. Phys. 105, 07B324 (2009) We investigate the structure of a recently proposed magnetic fluid consisting of shifted dipolar (SD) particles in an externally applied magnetic field via computer simulations. For standard dipolar fluids the applied magnetic field usually enhances the dipole-dipole correlations and facilitates chain formation whereas in the present system the effect of an external field can result in a break-up of clusters. We thoroughly investigate the origin of this phenomenon through analyzing first the ground states of the SD-particle systems as a function of an applied field. In a second step we quantify the microstructure of these systems as functions of the shift parameter, the effective interaction parameter, and the applied magnetic field strength. We conclude the paper by showing that with the proper choice of parameters, it is possible to create a system of SD-particles with highly interacting magnetic particles, whose initial susceptibility is below the Langevin susceptibility, and which remains spatially isotropic even in a very strong external magnetic field. © 2013 AIP Publishing LLC.

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Phase polarity in a ferrofluid monolayer of shifted-dipole spheres

Cited by 13 publications

References 46 publications

Quasi-2d fluids of dipolar superballs in an external field

Quasi-2d fluids of dipolar superballs in an external field

An analytic mean-field model for the magnetic response of a ferrofluid monolayer

Microstructure and magnetic properties of magnetic fluids consisting of shifted dipole particles under the influence of an external magnetic field

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