Itinerant-electron theory of spin waves in hcp cobalt

A key component in the itinerant-electron theory of spin waves in ferromagnetic transition metals is the model used for the exchange matrix elements. The present work describes how, within a tight-binding formalism, the complete set of matrix elements can be expressed in terms of a minimal number of parameters by invoking all the constraints imposed by the symmetry of the system. The theory is used to predict the spin-wave spectrum of hcp cobalt. It is found that the spectrum (at least in the Gamma-A direction) is rather insensitive to model details throughout most of the wave-vector range apart from a small. region around the reciprocal lattice points.