Annealing induced changes of the optical anisotropy of magnetic garnet films

Abstract

Films of pure and (Bi,Al) substituted yttrium iron garnet were grown by liquid phase epitaxy on [110] oriented gadolinium gallium garnet substrates. They will be characterized by a parallel and a perpendicular anisotropy, Δε∥ and Δε⊥, according to the direction of the electric field in the film plane and perpendicular to it. Both anisotropies are partly stress induced, due to the mismatch of lattice constants between film and substrate, and partly growth induced. It is mainly the growth induced contribution which can be influenced by annealing. For both groups of garnet films investigated the absolute values of the growth induced contributions to the anisotropies increase with the growth rate. The strongest increase of about 2.5·10-2 (μm/min)-1 has been observed for the perpendicular anisotropy of the (Bi,Al)-YIG films. The crystals were annealed in reducing and oxidizing atmospheres at different temperatures. Annealing in oxygen above 1000°C causes a strong reduction of the growth induced anisotropy and makes the total anisotropy approach the stress induced value. Furthermore, it is shown that phase matching can be achieved by annealing and by choosing a proper direction of mode propagation in the film plane. Nearly 100% TE-TM mode conversion is obtained in agreement with calculations.