Characterization of epitaxial La_0.7Ba_0.3MnO₃ structures using ferromagnetic resonance

We have compared a single layer of La_0.7Ba_0.3MnO₃ and a trilayer structure of SrTiO₃/La_0.7Ba_0.3MnO₃/SrTiO₃, both grown epitaxially on a LaAlO₃ substrate, using information obtained by ferromagnetic resonance (FMR). The trilayer samples have a more uniform magnetization and are not susceptible to environmental degradation. This may be due to the strain relief that the buffer SrTiO₃ layer provides for the La_0.7Ba_0.3MnO₃ layer. We have also studied the magnetic homogeneity of the trilayer structure as a function of the deposition temperature. The perpendicular FMR linewidth, Γ_⊥, shows a clear window in the deposition temperature where the linewidth is <50 Oe. However, the parallel linewidth, Γ_∥, is nearly ten times larger than Γ_⊥ with only a weak dependence on the deposition temperature. This broadening of the parallel linewidth compared to the perpendicular linewidth can be explained by invoking a local unidirectional anisotropy in the plane of the film.