Penetration of a radiofrequency electromagnetic field through plates of lanthanum manganites La_(0.85)Pb_(0.15)MnO_3, La_(0.60)Pb_(0.40)MnO_33, and La_(0.68)Y_(0.07)Ba_(0.25)MnO_3 has been studied in a frequency range of/= 20 kHz-300 MHz and at a frequency of 7.4 GHz under conditions where the thickness of the skin layer is both much greater and much lower than the sample thickness. The measurements have been performed in a temperature range including the magnetic phase transition. It is shown that, in spite of the similarity of static properties, the dynamic properties of the manganites studied differ substantially and that the differences are pronounced more strongly in the frequency range above 1 MHz. In the ferromagnetic region, significant changes in the penetration coefficient occur upon magnetization for all compositions. The initial dynamic magnetic permeability has been estimated. Due to the effect of dispersion, the decrease in the dynamic magnetic permeability in manganites doped with lead begins at frequencies on the order of a few MHz; in the manganites doped with barium and yttrium, substantial changes in the coefficient of penetration of electromagnetic field are observed up to frequencies on the order of 200 MHz. The changes in the penetration coefficient in the ferromagnetic region are primarily due to changes in the dynamic magnetic susceptibility rather than in the magnetoresistance.
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