Field-Induced Layer Formation in Dipolar Nanofilms

Abstract

Using molecular dynamics simulations, we demonstrate that the layering of confined colloidal particles with dipolar interactions, such as ferrofluids, in slablike geometries can be controlled by homogeneous external fields. For suitable surface separations, strong fields directed perpendicular to the film plane do not only align the particles but create additional layers in the system. The reverse effect occurs with an in-plane field which can induce a collapse of layers. Both effects are accompanied by pronounced particle rearrangements in lateral directions. Our simulation results are consistent with recent experiments of ferrofluids at surfaces.

Field-induced layering of confined ferromagnetic nanoparticles: the role of attractive interactions

“…Moreover, extending the systems somewhat into the third dimension the lateral structures are supplemented by structure formation in vertical direction such as layering. This has been shown in recent experiments of ferrofluids [10] and related computer simulation studies [11,12].…”

“…Indeed, as we have recently demonstrated via Molecular Dynamics (MD) simulations for confined SM particles [11,12], external (homogeneous) magnetic fields directed parallel or perpendicular to the confining surfaces can "trigger" the formation or destruction of layers present in zero field. The surface separations where this becomes possible can be inferred from the location of maxima and minima of the normal pressure as function of the wall separation [11]. We also observed [12] interesting structure formation within the layers such as a hexagonal-like ordering in dense systems subject to parallel fields.…”

Phase diagram of colloidal spheres in a biaxial electric or magnetic field

“…7 In this work, it was shown that three new crystal structures, i.e., hexagonal-close-packed ͑hcp͒, body-centered-tetragonal, and body-centeredorthorhombic phases, can be stabilized by applying an external uniaxial field. For completeness, we mention that the behavior of colloidal particles with permanent dipole moments in external fields [8][9][10] and in confinement 11,12 has been widely investigated as well.…”

Phase transitions and ordering of confined dipolar fluids

“…Theoretical [1][2][3], computer simulation [4][5][6][7][8][9], and experimental [10,11] studies have provided significant information about the orientational and spatial arrangement of dipolar particles in the vicinity of solid walls. The strongly anisotropic and long-ranged character of dipolar forces causes particular difficulties for the theoretical description of these systems.…”