Resonance-Based Detection of Magnetic Nanoparticles and Microbeads Using Nanopatterned Ferromagnets

Abstract

Biosensing with ferromagnet-based magnetoresistive devices has been dominated by electrical detection of particle-induced changes to the devices' static magnetic configuration.There are however potential advantages to be gained from using field dependent, high frequency magnetization dynamics for magnetic particle detection. Here we demonstrate the use of nano-confined ferromagnetic resonances in periodically patterned magnetic films for the detection of adsorbed magnetic particles with diameters ranging from 6 nm to 4 µm. are observed for a large range of coverages, even when hole-localized particles are covered by quasi-continuous particle sheets. For large particles however, preferential adsorption no longer occurs, leading to resonance shifts with polarities which are independent of the mode localization. Analogous shifts are seen in continuous layers where, for small particles, the shift of the layer's fundamental mode is typically about 10 times less than in patterned systems and induced by relatively weak fields emanating beyond the particle in the direction of the static applied field. This highlights the importance of having confined modes consistently positioned with respect to nearby particles.

Nanoparticle-Modified Magnetic Vortex Dynamics

“…For simplicity, most simulations are carried out in zero external magnetic field and we artificially set M S,P (the MNP's M S ) to 200 kA/m (the dipole moment is calculated as 4 3 πR 3 P M S,P ). Note that a (relatively easy to generate) 200 mT field can induce this moment in magnetically clustered MNPs [27] and this (field-dependent, non-saturated) moment has been successfully used in simulations to reproduce experimentally observed MNP-modified resonances [28]. We will however confirm that comparbale results are obtained in a finite OOP field.…”

“…MNP fields can however also modify vortex dynamics (and statics) [9], [11] and these dynamics can be probed electrically [17], [18], [26], opening pathways for vortexbased, electronic biosensors [21], [11]. Magnetic biosensing techniques that are based on (electrically) detecting changes in the frequency of resonant magnetization dynamics [20], [27], [28], [29] contrast the more conventional approaches outlined above in that they can operate naturally in the frequency domain (typically ∼ 0.1−10 GHz). Other potential advantages of a frequency based approach include fast sensor response times (e.g., [30], [31]), highly promising size scalability [20] and a wide operational external field range [32], the latter enabling the generation of large particle moments [28].…”

Field-controlled ultrafast magnetization dynamics in two-dimensional nanoscale ferromagnetic antidot arrays

“…Ferromagnetic antidot lattices (magnetic thin films with periodic non-magnetic inclusions or embedded holes) have emerged as one of the strongest candidates for reconfigurable, effective media for SW propagation due to the larger propagation velocity (steeper dispersion) than nanodot lattices. They find potential applications in magneto-photonic crystals [ 9 ], ultrahigh density data storage media [ 10 ], frequency-based magnetic nanoparticle detectors [ 11 ], waveguides for SWs [ 12 – 13 ], spin-wave filters [ 14 ], spin-logic [ 15 ] and reprogrammable magnonic devices [ 16 ]. The edges of the antidots lead to quantization of SW modes due to lateral confinement as well as the generation of a periodically modulated internal magnetic field due to the demagnetization effect.…”

On-Chip Magnetic Bead Manipulation and Detection Using a Magnetoresistive Sensor-Based Micro-Chip: Design Considerations and Experimental Characterization

“…However, some of these do not allow precise and controlled SPB manipulation, resulting in low trapping efficiencies, while some are not designed for integration with magnetic sensors for detection of SPBs. More recently, domain wall motion in nanometer thick permalloy patterns has been used to precisely transport SPBs to a target location [ 16 , 17 ] as well for detection of SPBs [ 18 , 19 , 20 , 21 , 22 ]. However, these devices employ bulky off-chip electromagnets or permanent magnets as magnetic field generators, which must be aligned to features on the micro-device.…”