where μ μ 0 is the vacuum permeability, μ μ e is the electron magnetic moment, μ μ B is the Bohr magneton, ℏ ℏ is the reduced Planck constant, and the g-factor cancels with the spin S = ± ± ℏ ℏ / 2 . The ± ± indicates that the sign is positive (negative) when the electron spin component in the direction of H is parallel (antiparallel) to the magnetic field.