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Large area MTJs with linear response and very larger sensitivities are needed to fulfill the requirements for the detection of pT/Hz0.5 magnetic fields at low frequency and room temperature. MTJ stacks with soft-pinned sensing layers have been developed and the stack was optimized, providing a tunable soft-pinning field over a large range of values. Sensitivities corresponding to resistance changes of up to 7%/Oe are obtained in patterned MTJs with areas of 20 × 20 μm2 starting from films with high sensitivity soft-pinned layers made from 3.0Co40Fe40B20/0.21Ta/8.0Ni81Fe19/8.0Ir20Mn80.
Date of Publication: Nov. 2012