Manipulation of free-layer bias field in giant-magnetoresistance spin valve by controlling pinned-layer thickness

The manipulation of the bias field of the free-layer in giant magnetoresistance spin-valves is of great importance in sensor applications because this feature dominantly affects the low-field sensitivity of magnetoresistance. In this study, it is demonstrated that the bias field of the free-layer can be manipulated by controlling the thickness of the pinned-layer deposited afterward. The key to success is the utilization of the magnetostatic interactions between the free-poles formed on the Néel walls in both free- and pinned-layers. Magnetostatic interactions play a role in stabilizing the antiparallel magnetization state and hence in suppressing the magnetization switching of the free-layer from an antiparallel to a parallel state. A nearly zero bias field is achieved for a Ta-buffered sample with a pinned-layer thickness of 1.75 nm, where a very high low-field sensitivity of 7.7 mV/mA·Oe is obtained.