Comparative analysis of several GMR strip sensor configurations for biological applications

• We modeled a spin valve GMR sensor and its interaction with magnetic nanoparticles.
• We experimentally verify the model with good accuracy.
• Sensor stray fields play a very significant role for our chosen geometry.
• Results depend on the film stack design and optional sensor isolation trenches.
• Our model guides optimization of signal generation from AC fields with DC offset.

Giant magnetoresistance (GMR) sensor strips are fabricated and modeled with the purpose of detecting a uniform distribution of Fe3O4 magnetic nanoparticles (MNPs) for biological application. We find that the free and fixed layers of GMR sensors play a dominant role in exciting the MNPs, and consequent MNP stray fields lead to increased free layer susceptibility. This result persists even when MNPs are confined to the interior of the sensing region but is enhanced when MNPs are allowed near exterior edges. Our analysis includes three different fabrication configurations on two different spin valve film stacks and agrees well with experimental results.