Improvement in spin-wave resonance characteristics of epitaxial barium-ferrite thin films by using an aluminum-doped strontium-ferrite buffer layer

We report on the effects of using $SrFe7Al5O19$ as a buffer layer for growth of high-quality epitaxial barium-ferrite thin films on sapphire substrates. X-ray diffraction studies reveal that the buffer layer causes the interfacial strains in the barium-ferrite films to relax. As a result, the ferromagnetic resonance linewidth decreases even in the as-deposited case. However, the more striking result is the drastic reduction in the linewidth that occurs when the barium-ferrite film is deposited on the buffer layer and subsequently annealed at $1000 °C$ for 2 h, allowing the observation of a large number of spin-wave resonances (up to the 15th mode), indicating an improvement in both the surface and interface characteristics.