Effect of the stray field of Fe/Fe3O4 nanoparticles on the surface of the CoFeB thin films

Abstract

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.

Effect of Fe/Fe3O4 Nanoparticles Stray Field on the Microwave Magnetoresistance of a CoFeB/Ta/CoFeB Synthetic Ferrimagnet

“…We derived the angular dependence tg­(γ)­(θ) in the platform covered with a cluster of NPs of 140 nm radius in external field H in the AP+ state (line 5 in Figure b). Line 5 did not follow the experimental data, though we chose a particle diameter of 140 nm equal to the average diameter determined from AFM microscopy for the same sample in ref . For this reason, we adjusted the radius of the NP cluster to 560 nm for a better coincidence of the calculated orientation dependence (line 6 in Figure b) with the experimental data.…”

“…The solution was dried, and the remaining NPs were strongly fixed on the sample, which allowed for transportation to a SQUID or an ESR spectrometer. Careful measurements of the NPs by atomic force microscopy (AFM)similar to those described in refs , revealed agglomeration of the NPs in clusters despite ultrasound dispersion. The AFM images in Figure S2b,c and a series of similar images are used to plot the cluster size distribution.…”

“…We experimentally analyzed the local area under the action of a particle and revealed enlarged areas of reversed magnetization by SQUID magnetometry and magnetic force microscopy . Micromagnetic modeling of the spin-valve films under the NP stray fields shows a complicated structure with various types of magnetization reversal .…”

“…We experimentally analyzed the local area under the action of a particle and revealed enlarged areas of reversed magnetization by SQUID magnetometry and magnetic force microscopy . Micromagnetic modeling of the spin-valve films under the NP stray fields shows a complicated structure with various types of magnetization reversal . Additional factors such as demagnetization of the NPs themselves, easy-axis rotation of the NPs, and a nonmagnetic gap between the NPs and ferromagnetic platform were revealed and experimentally observed. , Nevertheless, most of the experimental data are related to the current–voltage characteristics of a spin valve covered by NPs. − A deeper understanding of these results was obtained by analyzing the local magnetization and resistance of a spin valve covered by NPs.…”

“…19 We experimentally analyzed the local area under the action of a particle and revealed enlarged areas of reversed magnetization by SQUID magnetometry 20 and magnetic force microscopy. 21 Micromagnetic modeling of the spinvalve films under the NP stray fields shows a complicated structure with various types of magnetization reversal. 21 Additional factors such as demagnetization of the NPs themselves, easy-axis rotation of the NPs, and a nonmagnetic gap between the NPs and ferromagnetic platform were revealed and experimentally observed.…”