Phase separation of antiferromagnetic ground states in systems with   imperfect nesting
  We analyze the phase diagram for a system of weakly-coupled electrons having an electron- and a hole-band with imperfect nesting. Namely, both bands have spherical Fermi surfaces, but their radii are slightly different, with a mismatch proportional to the doping. Such a model is used to describe: the antiferromagnetism of chromium and its alloys, pnictides, AA-stacked graphene bilayers, as well as other systems. Here we show that the uniform ground state of this model is unstable with respect to electronic phase separation in a wide range of model parameters. Physically, this instability occurs due to the competition between commensurate and incommensurate antiferromagnetic states and could be of importance for other models with imperfect nesting. 
A.L. Rakhmanov, A.V. Rozhkov, A.O. Sboychakov, Franco Nori
cond-mat.str-el