Coexistence of ferro- and antiferromagnetism and phase transitions in itinerant electron systems

It is shown from a general point of view that the coexistence of ferro- and antiferromagnetism with a symmetry-breaking is possible in certain itinerant electron systems where the wave vector dependent susceptibility χ_q⁰ without the electron-electron interaction has two peaks at q = 0 and q = Q, the antiferromagnetic vector. The conditions for the coexistence and the possible phase diagrams in the H-T plane and the nature of phase transitions are discussed.