Comment on "Origin of intrinsic Gilbert damping".

The intrinsic Gilbert [1] magnetic damping of ferromagnetic resonant systems is a problem of long-standing interest. Recently, Hickey and Moodera [2] asserted that the spin-orbit interaction which arises from the nonrelativistic limit of the Dirac equation may be responsible for the intrinsic ferromagnetic linewidth. The theoretical methods employed by Hickey and Moodera involve previously developed formalisms wherein effective Hamiltonians have non-Hermitian parts; i.e., effective Hamiltonians of the form