We theoretically investigate a model with electrons and holes whose Fermi surfaces are perfectly nested. The fermions are assumed to be interacting, both with each other and with the lattice. To suppress inhomogeneous states, a sufficiently strong long-range Coulomb repulsion is included into the model. Using the mean field approximation, one can demonstrate that, in the absence of doping, the ground state of such a model is insulating and possesses a density-wave order, either spin-density wave or charge-density wave. Upon doping, a finite ferromagnetic polarization emerges. It is argued that the mechanism driving the ferromagnetism is not of the Stoner type. A phase diagram of the model is constructed and various properties of the ordered phases, such as half-metallicity and cone magnetic structure, are studied.

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• Charge density waves
• Ferromagnetism
• Landau theory
• Phase diagrams