We study ionic magnetic colloidal dispersions, which are constituted of gamma-Fe2O3 nanoparticles dispersed in water, and stabilized with electrostatic interparticle repulsion. The phase diagram piV versus phi (pi: osmotic pressure, V: particle volume, phi: particle volume fraction) is explored, especially in the range of high pi and high phi. The osmotic pressure pi of the colloidal dispersion is known either by a measurement either because it is imposed during the sample preparation by osmotic compression. The structure of the colloidal dispersion is determined from Small Angle Neutron Scattering (SANS). Two regimes can be distinguished. At high pressure, fluid and solid phases can exist. Their structure is governed by strong electrostatic repulsion, the range of which is here evaluated. At low pressure, gas, liquid and glassy solids can exist. Their structure results from a sticky hard sphere potential.