Variable exploration of micromagnetic simulations of concentration detection range of large area low aspect ratio GMR sensors in biomedical diagnostics

Biosensors employing magnetic nanoparticles (MNPs) and giant magnetoresistance (GMR) sensors offer the potential for zeptomole-level detection sensitivity [G. Binasch et al., Phys. Rev. B 39(7), 4828 (1989) and M. N. Baibich et al., Phys. Rev. Lett. 61(21), 2472 (1988)] While most research has centered on stripe-shaped sensors, large-area sensors with low aspect ratios have demonstrated linear response characteristics through the mechanism of reverse nucleation domains [D. R. Baselt et al., Biosens. Bioelectron. 13, 731–739 (1998) and B. Srinivasan et al., Angew. Chem., Int. Ed. 48, 2764–2767 (2009)] Prior studies in this domain [L. Xu et al., Biosens. Bioelectron. 24, 99–103 (2008)] have revealed that the dynamic range of these large-area, low-aspect-ratio GMR sensors typically saturates across a few orders of magnitude, with variations in MNP properties further influencing system sensitivity. This work leverages micromagnetic simulations to investigate variables for expanding the operational range of such sensing systems. Specifically, we examine the impact of GMR sensor geometries with varying aspect ratios, as well as the effects of nanoparticle-to-free-layer surface spacing—parameters that can be readily incorporated during design. Additionally, we explore techniques to accelerate simulations and conduct sensitivity analyses by evaluating characteristics of the reverse nucleation domains.