Sensing magnetic nanoparticles using nano-confined ferromagnetic resonances in a magnonic crystal

Abstract

We demonstrate the use of the magnetic-field-dependence of highly spatially confined, GHz-frequency ferromagnetic resonances in a ferromagnetic nanostructure for the detection of adsorbed magnetic nanoparticles. This is achieved in a large area magnonic crystal consisting of a thin ferromagnetic film containing a periodic array of closely spaced, nano-scale anti-dots. Stray fields from nanoparticles within the anti-dots modify resonant dynamic magnetisation modes in the surrounding magnonic crystal, generating easily measurable resonance peak shifts. The shifts are comparable to the resonance linewidths for high anti-dot filling fractions with their signs and magnitudes dependent upon the modes' localisations (in agreement with micromagnetic simulation results). This is a highly encouraging result for the development of frequencybased nanoparticle detectors for high speed nano-scale biosensing.Magnetic biosensors, in which biological analytes are tagged with magnetic nanoparticles (MNPs), have excellent potential for solid-state point-of-care medical diagnostics 1-3 . The technique is intrinsically matrix-insesntive 1 , can compete with industry-standard immunoassays 4 and can be combined with magnetic separation methods 5 . The central element of a magnetic biosensor is a detector for the stray or 'fringing' magnetic fields generated by magnetised MNPs which are used to label, typically in-vitro, analytes of interest within a biological sample. Previously used sensors include SQuIDs 6 , Hall sensors 7 , ferromagnetic rings 8,9 and magneto-impedance devices 10 . However one of the most widely used methods is that employing magnetoresistive (MR) magnetic field sensors [1][2][3][4][5][11][12][13][14] which are typically fabricated with at least one

Microwave magnetic dynamics in ferromagnetic metallic nanostructures lacking inversion symmetry

“…[1][2][3][4][5][6][7][8][9][10][11][12]). These materials are important for the emerging fields of magnonics [13], microwave spintronics [14][15][16][17], and for novel sensor applications [18][19][20][21].…”

“…[1][2][3][4][5][6][7][8][9][10][11][12]). These materials are important for the emerging fields of magnonics [13], microwave spintronics [14][15][16][17], and for novel sensor applications [18][19][20][21].Macroscopically-long stripes with sub-micron cross-section made of ferromagnetic materials have attracted a lot of attention, because this geometry is a very convenient model object for studying the impact of geometric confinement on magnetization dynamics on the sub-micrometre and nanometer scales [22][23][24][25][26][27][28][29][30]. The main reasons for the attractiveness of this geometry are the practical absence of a static demagnetizing field H ds when the external field is applied along the stripes (i.e.…”

Frequency-based nanoparticle sensing over large field ranges using the ferromagnetic resonances of a magnetic nanodisc

“…This results in a system of linear differential equations for resonant oscillations of the magnetisation, dm(r, t), occurring around m 0 (r). This system of differential equations can be written as an eigenvalue problem 33 . The eigenvectors correspond to the resonant eigenmodes 60 of the nanodisc, each occurring at a resonant frequency given by the mode's eigenvalue.…”

“…This translates to a change in the device resistance, enabling electronic nanoparticle detection. However, one may also exploit the magnetic field dependence of ferromagnetic resonance for detection of magnetic fields [28][29][30][31][32] and thus magnetic nanoparticles [32][33][34][35][36][37][38] . Notably, the ferromagnetic resonance frequency within the device will respond directly to the field of the MNP (Fig.…”

Theoretical Study of the Stripline Ferromagnetic Resonance Response of Metallic Ferromagnetic Films Based on an Analytical Model

“…Also, the stripline geometry is important for various applications of magnetization dynamics, such as sensing fields, particles and substances [4][5][6] and in microwave spintronics [7].…”