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Bulk modulus of the nanoparticle system in concentrated magnetic fluids and local field-induced structural anisotropy

In the present study we probe the bulk modulus and the structure of concentrated magnetic fluids by Small Angle X-ray Scattering. The electrostatically stabilized nanoparticles experience a repulsive interparticle potential modulated by dipolar magnetic interactions. On the interparticle distance lengthscale, we show that nanoparticles are trapped under-field in oblate cages formed by their first neighbours. We propose a theoretical model of magnetostriction for the field-induced deformation of the cage. This model captures the anisotropic features of the experimentally observed scattering pattern on the local scale in these strongly interacting colloidal dispersions.