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