NMR study of Ga and Al substituted hexagonal ferrites with magnetoplumbite structure

⁵⁷Fe NMR spectra and relaxation rates in lead hexaferrite single crystals PbFe₁₂O₁₉, PbFe_12-xGa_xO₁₉, (x=0.42, 1.2) and PbFe _12-xAl_xO₁₉, (x=0.21) have been measured at 4.2 K using spin echo technique. Besides the main lines corresponding to the nonequivalent positions of Fe³⁺ ions in the magnetoplumbite structure, the satellite lines caused by substitution in the vicinity of resonating nuclei have been observed. The dependence of the NMR spectrum on the external magnetic field has been used to separate the overlapped satellites from different iron sites. The most distant satellites have been assigned to the resonance of iron nuclei at 4f₁ site with substitution at 12 k and 2a sites in their vicinity. A strong preference of 2a site for Al substitution has been found