Here μ μ eff is effective relative complex permeability of the mixture, μ μ d is relative complex permeability of the background medium containing small spherical inclusions of relative permeability μ μ m with volume fraction of c m ≪ ≪ 1 . This formula was derived in dipole approximation. Magnetic octupole mode and all other magnetic oscillation modes of odd orders were neglected here. When μ μ m = μ μ d and k m a ≪ ≪ 1 this formula has a simple form