Exchange anisotropy in NiFe/NiO/CoPt trilayers

NiFe/NiO bilayers and NiFe/NiO/CoPt trilayers with various NiO thicknesses were prepared by RF magnetron sputtering under a dc magnetic field of 70 Oe, and their magnetization process and exchange coupling have been investigated. In the NiFe(5 nm)/NiO bilayers, the unidirectional coupling field Hex does not appear when NiO is thinner than 10 nm. While in the NiFe(5 nm)/NiO(tNiO)/CoPt(5 nm) trilayers, Hex appears even when tNiO is 5 or 10 nm, and the direction of Hex was determined by the direction of the field applied during the deposition of NiFe layers. Accordingly the NiFe and CoPt layers are magnetically coupled through the NiO layer. When the thickness of NiO layer is as thick as 30 nm, the direction of Hex was determined only by the direction of the field applied during the deposition of NiFe layers.