Itinerant Antiferromagnetism

The itinerantly antiferromagnetic or spin-density-wave state is examined for an electron gas and a more realistic band model. The paramagnetic electron gas, which is unstable to the formation of an antiferromagnetic state in the Hartree-Fock approximation, is shown to be stable when either static Fermi-Thomas or dynamic screening is included. A mathematical model is constructed for the spin-density-wave state below its transition temperature and its experimental consequences examined. A criterion for itinerant antiferromagnetism in a band model is derived and shown to be consistent with the antiferromagnetism of Cr. A crude model is employed to compute qualitatively the thermodynamic and electromagnetic properties of an itinerant antiferromagnet like Cr. In particular, the specific heat, spin susceptibility, collective modes, and electromagnetic absorption are evaluated.