Exchange coupling and spin-flip transition of CoFe{sub}2O{sub}4/α-Fe{sub}2O{sub}3 bilayered films

摘要

CoFe{sub}2O{sub}4/α-Fe{sub}2O{sub}3 (ferrimagnetic/antiferromagnetic) bilayered films were prepared on α-Al{sub}2O{sub}3(102) single-crystalline substrates by helicon plasma sputtering. A well-crystallized epitaxial α-Fe{sub}2O{sub}3(102) layer was formed on the substrate, while CoFe{sub}2O{sub}4 grown on α-Fe{sub}2O{sub}3 (102) was a polycrystalline layer with a (100)-preferred orientation. The α-Fe{sub}2O{sub}3(102) films without CoFe{sub}2O{sub}4 layers clearly showed a spin-flip transition at about 400 K. The spins aligned perpendicular to the film plane at room temperature changed their direction within the film plane above 400 K. However the α-Fe{sub}2O{sub}3 base layers of CoFe{sub}2O{sub}4/α-Fe{sub}2O{sub}3 bilayered films did not show any spin-flip transition. The CoFe{sub}2O{sub}4 layer on α-Fe{sub}2O{sub}3 had a large in-plane magnetic anisotropy, while the spin axis of the α-Fe{sub}2O{sub}3 (102) base layer was directed perpendicular to the film plane. The magnetization of ferrimagnetic CoFe{sub}2O{sub}4 layers was coupled perpendicularly to the spin axis of anitiferromagnetic α-Fe{sub}2O{sub}3 layers due to the exchange coupling at the interface between CoFe{sub}2O{sub}4 and α-Fe{sub}2O{sub}3.