Abstract
Absorption of electromagnetic waves by La0.68Y0.07Ba0.25MnO3 and La0.67Sr0.33MnO3 manganites at the frequencies 5.44, 7.48 and 8.94 GHz was investigated experimentally. The ferromagnetic resonance (FMR) and ferromagnetic antiresonance (FMAR) were observed as microwave absorption versus applied magnetic field dependences. The relative contribution of FMR and FMAR depends on the sample size, microwave frequency and position of the sample in the cavity. The shape of the microwave absorption curves depends critically on the type of the resonator mode and mutual orientation of high frequency and static magnetic fields. The applicability of the thin-film model for the theoretical description of ferromagnetic resonance in bulk samples was verified. It is shown that the FMR linewidth for bulk polycrystalline manganites is determined by two major factors: porosity and nonuniform broadening. The FMR linewidth is larger for the highest modes having the smaller lateral scale. The FMAR curve is more symmetric than the FMR one.
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