Effective Demagnetizing Factors in Ferromagnetic-Resonance Kittel Equation

Simple equations of effective demagnetizing factors N x e and N y e for use in Kittel's ferromagnetic resonance (FMR) formula have been derived for the first time. The effective demagnetizing factors are derived from anisotropy energy ( G ) and a static field direction expressed by a spherical coordinate system (θ,φ). Using the equations, the resonance equation at every direction can be easily calculated without the need for crystal-axis rotation. Compared with Macdonald's derivation, our derivation is simple.