Canted exchange bias in antiparallel biased spin valves

Abstract

Conventional spin valves consist of two magnetic layers, one of which is pinned by exchange bias to act as a reference magnetic layer in giant magnetoresistance measurements. Antiparallel biased spin valves feature a Co/Ru/Co trilayer in place of this pinned layer, where the Co layers are strongly antiferromagnetically coupled. This leads to hugely enhanced pinning since an applied field will exert opposite torques on the Co layer moments. Spin valves are typically deposited in a magnetic field to define magnetic anisotropies, and the development of magnetic structure in the pinned AF couple is not trivial under these conditions. The resultant moment of the AF couple is found to slowly rotate as the final Co layer is deposited. This results in canted pinning once the exchange bias layer is added. There appears to be some magnetic friction as the Co layers rotate during growth. The rotation means that the pinning direction can take any angle with respect to the growth field, leading to positive or negative (or even orthogonal) exchange bias.