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Magnetite–Polymethylmethacrylate Core–Shell Nanocomposites: Applications in All-Optical Magnetometers
Palash Gangopadhyay, Alejandra Lopez-Santiago, Ramakrishna Voorakaranam, Roland Himmelhuber, Charles Greenlee, Jayan Thomas, André Persoons, Robert A. Norwood, Thierry Verbiest, Hitoshi Yamada and N. Peyghambarian

A method has been developed to prepare magnetite nanoparticles core polymer shell nanocomposite. These core shell nanocomposite particles can be further cross-linked into a passive polymer host that provides processable material with high optical transparency and large Verdet constants.Wavelength dependent and saturation Faraday rotation (FR) measured at room temperature in a polymer containing varying concentrations of cross-linked magnetite core poly(3-methyl)methacrylate (PMMA) shell nanocomposite particles has been explained using a long range magnetic field interaction model. The magnitude of the FR in these composites appears to be strongly dependent on the concentration of the particles, the wavelength of measurement, and the size and shape of the nanoparticles. Comparison of the figure of merit of 2.1 in these core-shell nanocomposites to that of 4.2 for yttrium iron garnet at 980 nm indicates that these nanocomposites may find applications in various magnetic and magnetooptic sensors and devices. Using these observations an all-optical magnetometer has been constructed based on magnetite core polymer shell nanocomposite material. A noise equivalent magnetic field sensitivity of 5 nT/√Hz was observed using a 1 μT 500 Hz control magnetic field.

Keywords: Magnetometer, Faraday rotation, polymer, magnetite nanoparticles, core shell.

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