Magneto-optic polymer composites for optical isolation and magnetic field sensing

The design, synthesis and study of magneto-optic (MO) nanocomposite materials with magnetic nanoparticles embedded in a non-magnetic host matrix, have attracted significant interest over the last decade. These mesoscopic materials are expected to exploit magnetic and optical properties of the nanoparticles alongside the ease of processability of the host. Such MO active nanocomposites may find application in magnetic field sensors, integrable optical isolators and circulators, high speed MO modulators and information storage. Although the properties of isolated single domain magnetic nanoparticles are well understood, the correlation effects in single particle response in mesoscopic systems continue to be an area of intense research. A critical challenge in assembling a nanocomposite material is to achieve a uniform dispersion of the nanoparticles in the polymer host matrix with minimal clustering. It is preferable for nanoparticles to be chemically fixed to the matrix material inhibiting migration and aggregation during composite post processing. Our two-step approach consists of:

creating a polymer shell on the particle surface and
chemically linking the shell to the host matrix.

A schematic of this process is shown below:

Creating a polymer shell on the particle surface and chemically linking the shell to the host matrix

Fe₃O₄ (magnetite) core – polymer shell nanoparticle/PMMA matrix composites have been prepared with little or no aggregation as shown – the inset illustrates the uniform polymer shell that is created around each magnetite nanoparticle; unlike previously reported approaches, these composites have an appreciable degree of optical transparency in the visible and near-IR region. We have also found that the Faraday rotation exhibited by this composites and their corresponding Verdet constants show a strong dependence on particle concentration and wavelength, indicating that interparticle correlations play a role in determining the properties of these unique composites.

Uniform polymer shell that is created around each magnetite nanoparticle

References

A. Lopez, Santiago, P. Gangopadhyay, J. Thomas, R. A. Norwood, A. Persoons, and N. Peyghambarian, "Faraday rotation in magnetite-polymethylmethacrylate core-shell nanocomposites with high optical quality," Appl. Phys. Lett. 95, 143302 (2009).
P. Gangopadhyay, R. Voorakaranam, A. Lopez-Santiago, S. Foerier, J. Thomas, R. A. Norwood, A. Persoons, and N. Peyghambarian, "Faraday rotation measurements on thin films of regioregular alkyl-substituted polythiophene derivatives," J. Phys. Chem. C 112, 8032 (2008).