Magnetic moments in the Poynting theorem, Maxwell equations, Dirac equation, and QED

The role of magnetic moments in classical and quantum electrodynamics is examined in this work. The effects are described by a classical extended Poynting theorem and extended Maxwell equations and by conventional quantum electrodynamics expressed in terms of electromagnetic fields. Both descriptions take into account energetics of the interaction of magnetic moments with inhomogeneous magnetic fields. We show how magnetic moment effects are included in either version of electrodynamics and that these apparently different formulations can give consistent results. In either case, we express the interactions in terms of electromagnetic fields only, avoiding use of a vector potential. The main focus is on magnetic dipole interactions, and magnetic monopole interactions are not considered.