Ferromagnetic resonance and intrinsic properties of La_0.67Ba_0.33MnO_z

Systematic magnetization and ferromagnetic resonance (FMR) measurements have been performed on thin-film samples of La_0.67Ba_0.33MnO_z (T_C∼340 K). It is found from the FMR data that asgrown films show broad lines whose width Γ increases to nearly 1 kOe as T reduced to 77 K. The increase roughly follows the increase in the magnetization suggesting magnetic inhomogeneity as the main cause for the rise in Γ. However, when films were properly annealed in O₂, we obtained narrow lines (Γ∼200 Oe at 10 GHz). Γ was effectively independent of temperature and linearly dependent upon microwave frequency, both of which are strong signs that, we have succeeded in obtaining a uniform, homogeneous manganite sample. Having gotten a uniform material, we have measured the intrinsic properties of this system.