Behavior of giant magnetoresistance in Co–Cu–Co pseudo spin-valves after magnetic annealing

Abstract

The Co/Cu/Co pseudo spin-valves were e-beam evaporated onto silicon substrates covered with thermal oxide. The X-ray diffraction and X-ray reflectivity showed polycrystalline layer structure and conformal interface roughness, respectively, giving rise to the Néel coupling. The longitudinal magneto-optical Kerr effect measurements revealed a deposition induced in-plane magnetic anisotropy in the thicker (magnetically hard) Co layer. The maximum giant magnetoresistance (GMR) ratio for magnetization along the hard axis was found to be by 30% higher than that for magnetization along the easy axis. A series of successive 1 hour thermal annealings from 100 °C to 350 °C in a saturation magnetic field applied along the easy axis lead gradually up to a 20% relative enhancement and reduction of GMR for magnetization along the hard and easy axes, respectively. This annealing behavior may be explained by a faster magnetic anisotropy growth in the thicker Co layer than in the thinner one due to the deposition induced anisotropy and better developed starting polycrystalline structure as expected for larger thickness. An annealing induced 0.8 kA/m reduction of the Néel coupling derived from modified interface parameters and annealing out of defects play a secondary role in GMR modification.