Crystalline anisotropy effects on magnetoresistance in epitaxial spin-valve sandwiches with antiferromagnetic NiO films

We have synthesized a series of bottom and symmetrical spin valve sandwiches of Co/Cu/Co/NiO on single crystal substrate including MgO (1 0 0), (1 1 0) and (1 1 1) orientations and SrTiO3(1 0 0) by molecular beam epitaxy. High MR ratio (5-8%) and strong angular dependence on H-c and MR have been observed from most samples. These results are inconsistent with the argument that spin coupling only exists on(1 1 1) orientation and further provide direct information on the symmetry of the magnetic exchange anisotropy. it also implies that a texture film potentially may provide higher MR ratio than a polycrystalline film if other extrinsic properties can be also controlled. (C) 1999 Elsevier Science B.V. All rights reserved.