title: Shape-dependent force between magnetic nanoparticles in a colloidal ferro-fluid.
abstract: In the presence of applied magnetic fields, magnetic nanoparticles suspended in a colloidal ferrofluid align themselves in chains if the inter-particle force due to induced dipolar interactions within the chain dominates over the thermal randomization. The variation of this chain force with the interparticle separation and particle volume has been studied in the past for the special case of spherical particles. In the present paper the dependence of the chain-force on the shape of the suspended nanoparticles of prolate spheroidal type has been investigated. Starting with the case of a sphere (eccentricity e = 0), the shape is evolved by varying the eccentricity of the spheroid up to the limiting case of a nano-rod (eccentricity e = 1) while keeping the particle volume and the inter-particle separation fixed. For the first time in our knowledge, the expressions for the bulk susceptibility and hence the induced magnetization of ellipsoidal nanoparticles have been derived and used for the present problem. The variation of chain-force with the inter-particle separation for a fixed shape is also presented.
authors.affiliation: Department of Physics, Indian Institute of Technology-Bombay, Powai, Mumbai 400076, India.
authors.forename: Saurabh
authors.initials: S
authors.lastname: Sharma
authors.forename: Gautam
authors.initials: G
authors.lastname: Mukhopadhyay