Magnetic anisotropy due to spin-orbit and dipole-dipole interactions in spin-density-wave antiferromagnets

The first effort to construct a theory of uniaxial magnetic anisotropy for an incommensurate spin-density-wave antiferromagnet like chromium is presented. The theory incorporates the spin-orbit and magnetic dipole-dipole interactions into a model for the magnetic ground state, using an idealized model band structure. The magnitude of the result is easily large enough to account for the uniaxial anisotropy of chromium. However, the temperature dependence of the anisotropy from both mechanisms is that of the antiferromagnetic gap squared. Therefore, a zero crossing of the anisotropy, as required to explain the spin-flip transition in chromium, does not occur. This indicates that for chromium the detailed band structure must be taken into account, or an additional mechanism is operative.