Texture and surface/interface topological effects on the exchange and coercive fields of NiFe/NiO bilayers

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Abstract
The texture and surface/interface topological effects on the exchange field Hex and coercivity Hc in rf-sputtered NiO/NiFe bilayers were studied. The NiO/NiFe bilayers with NiO crystalline textures of (111), (200), and (220), and different surface/interface roughness, were fabricated by changing the sputtering conditions. The Hex of the NiO/NiFe bilayers was inversely proportional to the thickness of NiFe. The NiO/NiFe bilayers with different NiO textures of (111) dominant, (200) dominant, or combinations of (111), (200), and (220), respectively, showed almost the same dependence of Hex on NiFe thickness. Thus, Hex was insensitive to the texture of NiO films. The surface/interface roughness has a significant effect on Hc of the NiO/NiFe bilayers. By controlling the sputtering process, NiO (45 nm)/NiFe (10 nm) bilayers with a Hex of 39 Oe, a Hc of 4.1 Oe, and an Hex/Hc ratio of 9.51 could be obtained. A new parameter of Hex/Hc was introduced to describe the exchange coupling and coercive properties in ferromagnet/antiferromagnet coupled bilayers. A large Hex/Hc ratio is very desirable for spin-valve structures.