Extra current channels in longitudinally biased magnetic tunnel junctions

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Abstract
Experiments on the longitudinal biasing of microsized magnetic tunnel junctions have been conducted using permanent magnets partially overlapping the junction area. The tunneling magnetoresistance ratio showed a strong dependency on the overlap length, since even a 10% overlap of the sensor length resulted in a 25% drop from its initial value without overlap. Analytical and micromagnetic analyses have demonstrated that this decrease comes from extra current channels, located in the regions below the permanent magnets, that shorted a large amount of the sense current from the central active region in the antiparallel magnetization state. The high uniaxial anisotropy field, induced by the permanent magnets in the overlapped regions, created particular magnetic configurations responsible for these low resistance paths. Several alternatives, using antiferromagnetic material in place of the permanent magnets or a modified design of the magnetic tunnel junction structure, are presented and discussed to prevent this extra current channel effect.