MAGNETIC-RELAXATION OF FE-57 NUCLEI OF MAGNETOPLUMBITES

The peculiarities of the spin-spin and spin-lattice relaxation rates for Fe-57 nuclei in magnetoplumbites were experimentally investigated within the temperature range of 4.2-295 K. It is found that for all Fe3+ sublattices the spin-spin and spin-lattice relxation exhibits maxima at 4.2-77 K. The temperature dependence of the FMR line width for the samples investigated by NMR is found to have a maximum at 170 K and the frequency of 59.3 GHz. The peculiarities of the electronic spin relaxation in Pb hexaferrite are directly related to the presence of Fe2+ ions and can be interpreted within the framework of the theory of slow relaxation induced by the valency exchange process Fe2+ reversible Fe3+. The valency exchange activation energy E = 2.5 . 10(-2) eV and the impurity ion relaxation time tau(x) = 0.53 ps. were determined on the basis of both FMR and NMR data. It is shown that the spin-spin relaxation rate is significantly greater in the domain walls than it is in the domains themselves.