Faraday rotators are ubiquitous in telecommunications, magnetic-sensing, and optical isolation, and are proposed to be key elements in optical circuitry. While most applications of Faraday rotators make use of inorganic garnet crystals, these are generally limited by low magneto-optical activity (low Verdet constants), high cost, and/or limited processing options. This has led to an interest in new materials and composites with improved activity and processing characteristics. We have developed a new type of magneto-optical (MO) polymer-nanoparticle composite that can be prepared by solution processing methods with tunable Verdet constant and device sensitivity. By grafting short-chain polymer ligands onto MO active CoFe<sub>2</sub>O<sub>4</sub> nanocrystals, nanoparticle dispersion in processible polymer matrices was greatly enhanced at up to 15 wt% inorganic loading. Employing a multilayer polymer film construct, functional Faraday rotators were prepared by sequential spin-coating of active nanocomposite and protective, barrier cellulose acetate layers. For these assemblies, MO activity and sensitivity can be easily tuned through variation of nanoparticle feed and control of polymer film layers, respectively. This enabled a predictable trend in MO-activity as a function of nanoparticle loading to be developed – a key contribution to the understanding of structure-property correlations for composite Faraday rotators. These Faraday rotators show up to a 10-fold enhancement in Verdet compared to reference terbium gallium garnets at 1310 nm, opening new possibilities for the fabrication of “plastic garnets” as low cost alternatives to existing inorganic materials for use in the near-IR.

Plastic garnets: polymer and magnetic nanoparticle faraday rotators with tunable magneto-optical activity

ACS Fall 2020 Virtual Meeting

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