Predicted coupling of the electromagnetic angular momentum density with magnetic moments.

Analytical derivations are developed to demonstrate that (i) the angular moment density associated with an electromagnetic field can directly couple with magnetic moments to produce a physical energy, (ii) this direct coupling explains known, subtle phenomena, including some recently predicted in magnetoelectric materials, and (iii) this coupling also results in novel effects, such as the occurrence of a magnetic anisotropy that is driven by antiferroelectricity.