Biaxial strain sensing using a Pd/Co-based perpendicular flexible spin valve

We fabricated a Pd/Co-based spin valve structure, which has in-plane (IP) free and out-of-plane (OOP) fixed layers, on a flexible substrate. By applying %-order biaxial tensile strain to the substrate, a spin reorientation transition from IP to OOP occurs in the free layer, resulting in a drastic change in the shape of the magnetoresistance curve. This change is reversible with increasing and decreasing strain. We suggest that our system could be utilized as an in-plane "direction-independent" strain sensor and as a pressure detector.