A flexible giant magnetoresistive device for sensing strain direction

Miniaturized strain sensors are of value in a variety of areas, including wearable devices and structural health monitoring. Strain gauges based on magnetoresistance effects have previously been developed and offer potential advantages over conventional devices. However, these approaches have so far focused on sensing only the magnitude of the strain. Here, we show that a flexible giant magnetoresistive device can be used to detect the direction of strain in a material. Our trilayer devices, which are fabricated on a flexible substrate, consist of a strain-sensitive ferromagnetic cobalt layer and a strain-insensitive ferromagnetic permalloy (NiFe) layer, separated by a non-magnetic copper layer. We also show that the strain-sensitive and strain-insensitive layers can be made from a single ferromagnetic material by engineering the magnetoelastic properties of cobalt layers. Our integration of spintronics and flexible electronics could lead to the development of a flexible sensor sheet capable of mapping local strain directions. The direction of strain in a material can be detected using flexible giant magnetoresistive devices that consist of a strain-sensitive free layer and a strain-insensitive pinned layer.