High giant magnetoresistance and thermal annealing effects in perpendicular magnetic [Co/Ni]N-based spin valves

The thermal stability and giant magnetoresistance (GMR) of pseudo- and FeMn-biased spin valves with perpendicular magnetic [Co/Ni](N) multilayer as free and reference layers are investigated. The observed GMR ratio for the pseudo-spin-valve is as high as 7.7%, but it rapidly decreases below 1.0% after annealing in a perpendicular field at 200 degrees C. Such poor temperature stability is ascribed to simultaneous switching of the free and reference multilayers caused by loss of their coercivity difference. In contrast, an FeMn-biased sample with a similar structure has a slightly lower GMR signal of 6.5% but exhibits much better thermal stability, with the GMR reduction occurring at an elevated anneal temperature of over 300 degrees C. This GMR reduction is due to Mn diffusion and a reduction in perpendicular anisotropy.