Nuclear Magnetic Relaxation in Ferromagnetic Transition Metals

The spin-lattice relaxation rates associated with the nuclear magnetic resonance in ferromagnetic transition metals, Fe, Co, and Ni, are studied theoretically. Thermal fluctuations of the internal magnetic filed at a nucleus associated with the spin wave excitation and the individual excitations corresponding to s - and d -bands are considered. The effect of the coupling between the spin waves and the conduction electrons is also considered. The d -band electrons are treated in a tight binding approximation. The predominant nuclear spin relaxation mechanism in all of these metals is shown to come from the fluctuation of the orbital current of the d -band electrons. The other possible mechanisms are shown to make smaller contribution than this by one to two orders of magnitude, except for the Fermi contact interaction of the s -band electrons in Fe and Co, which can possibly make a significant contribution, though not of primary importance.