Analytical and micromagnetic modeling for detection of a single magnetic microbead or nanobead by spin valve sensors

We present a simple analytical model based on the Stoner-Wohlfarth model for the detection of a single magnetic microbead or nanobead by spin valve sensors. Two-dimensional micromagnetic simulations were also performed for the spin valve sensors. It is found that the analytical model fits well with the micromagnetic simulations in the case of the microbead, although it underestimates the effect of a nanobead. Experiments were carried out to detect a single superparamagnetic microbead (Dynabeads(registration) M280, 2.8 (mu)m in diameter) on the fabricated spin valve sensors. The experimental results were found to be consistent with the analytical and micromagnetic models.