Direction dependent giant magnetoresistance of spin valves using epitaxial Cr₂O₃ as the pinning layer

We report the direction dependent magnetization and the giant magnetoresistance (GMR) data for the spin valves NiFe/Cu/NiFe/Cr₂O₃. The sample with the (1 1̄ 0 2) Cr₂O₃ showed typical spin valve properties after the magnetic field annealing (MFA) parallel to the [1̄ 1 1] direction; the exchange bias of ∼ 7 0 0 Oe and the highly asymmetric GMR effect of ∼ 4 % with the magnetic field sweep. However, the MFA perpendicular to the [1̄ 1 1] direction induced a symmetric GMR effect of ∼ 2.6 % without exchange bias. It is noticeable that the interface exchange coupling constant J by the (1 1̄ 0 2) Cr₂O₃ is maximally ∼ 0.27 erg / cm². On the other hand, the sample with the (1 0 1̄ 0) Cr₂O₃ showed no exchange bias in all directions but it displayed a symmetric GMR effect of 1.8-3.5% which was caused by a coercivity difference between two NiFe layers.