Characterization of Superparamagnetic Particles Mobility by On-Chip Micromagnets

We fabricate on-chip micromagnets using Ni
₈₀
Fe
₂₀
and Co
₇₀
Fe
₃₀
materials for the characterization of mobility of superparamagnetic particles. The maximum velocity of the particles around the periphery of the micromagnets is determined by the critical frequency, which indicates that the particle enters the phase-slipping regime from the phase-locked regime. The maximum velocity of NiFe micromagnets is approximately 3 times larger than that of CoFe micromagnets measured at the low field regions. Moreover, the maximum velocity of the particles is decreasing with increasing the thickness of Teflon coating on the micromagnets, which is in a good agreement with the variation of the magnetostatic potential energy evaluated numerically from micromagnetic simulations.