%0 Journal Article %T Bulk modulus of the nanoparticle system in concentrated magnetic fluids and local field-induced structural anisotropy %A E. Wandersman %A A. C¨¥bers %A E. Dubois %A G. M¨¦riguet %A A. Robert %A R. Perzynski %J Physics %D 2013 %I arXiv %X 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. %U http://arxiv.org/abs/1309.6523v1