Fe/Fe3O4 nanoparticles have been deposited on the surfaces of ultrathin CoFeB film andCoFeB/Ta/CoFeB hetero-structure to be detected due to the stray field generated by one particle or a cluster of particles. Exchange biased Fe/Fe3O4 core-shell nanoparticles have been used to stabilize the particles magnetization. Comparison between the Atomic Force and Magnetic Force Microscope images and subtraction of corresponding phase contrasts allows visualization of the film magnetization affected by the particles. Spectra of Ferromagnetic Resonance of the ultrathin films with deposited particles allow one to estimate particle/film dipolar interaction. The results will be useful for the development of lab-on-chip sensors of magnetically labeled cells. Estimation of particles number by magnetic response of the CoFeB heterostructure is demonstrated.
The
effect of the stray field of Fe/Fe3O4 nanoparticles
on the angular dependence of the microwave absorption
derivative in CoFeB/Ta/CoFeB synthetic ferrimagnetic structures and
CoFeB films with perpendicular anisotropy is analyzed, and its application
for sensor technology is proposed. The effective field of the “platform-particles”
system controlled by the magnetic dipole interaction of the CoFeB-Fe/Fe3O4 system decreased to zero in areas where the
platform was magnetostatically coupled with nanoparticles. Micromagnetic
modeling demonstrated the distribution of magnetization and resistance
in local areas of CoFeB/Ta/CoFeB structures under the nanoparticles.
The microwave absorption derivative can be used as an indicator of
local magnetization switching of the giant magnetoresistance (GMR)
structure under scattering fields of NPs or magnetically labeled cells.
The limiting sensitivity of the detection method was 2.4 × 107 nanoparticles, which covered the spin-valve surface. We have
proposed to combine the advantages of a GMR sensor with wireless technology
of microwave reading of magnetoresistance for the detection of magnetically
labeled cells.
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