Evidence for the stratification of epitaxial films of Y2.85La0.15Fe3.75Ga1.25O12 from microwave resonance measurements

Ferromagnetic resonance experiments on thin epitaxial films of Y_2.85La_0.15Fe_3.75Ga_1.25O₁₂, grown by a vertical dipping technique, provide strong evidence for stratification of these films. Perpendicular resonance spectra recorded after etching off the magnetic film step by step show resonances due to six strata in 4 μm thick films. Of each stratum the thickness has been determined as well as the magnetic anisotropy. It is found that the layer next to the interface is 0.4 μm thick and has a strongly negative $\text{K}{}_{\mathrm{u}}\text{(}\text{K}{}_{\mathrm{u}}\text{M}\text{= -400}\text{Oe}\text{)}$. Strata remote from the substrate are 1 μm thick and have a positive $\text{K}{}_{\mathrm{u}}\text{(}\text{K}{}_{\mathrm{u}}\text{M}\text{≈ + 150}\text{Oe}\text{)}$.