Self-Assembled Multi-Phase Heterostructures for Enhanced Magneto-Optical Anisotropy*

Magneto-optical coupling incorporates photon-induced change of magnetic polarization that can be adopted in ultrafast switching, optical isolators, mode convertors, and optical data storage for advanced optical integrated circuits. But integration of plasmonic, magnetic and dielectric properties in one single material system is challenging. We use a bottom-up self-assembling synthesis method to integrate multifunctional phases as a nanopillar-in-matrix thin film heterostructure that realizes epitaxial quality, sharp atomic interface and large throughput. Using titanium nitride (TiN) as a durable plasmonic matrix, a metal-free metamaterial platform with embedded nickel oxide (NiO) vertical nanorods that function as tunable ferromagnetic nanodomains has been demonstrated. Such a dissimilar ceramic-ceramic combination enables a strong hyperbolic dispersion in the visible and near infrared frequencies. More interestingly, when Au is introduced in the TiN-NiO heterostructure, a hybrid core-shell nanopillar array is formed where the two-monolayer Au shell serves to release the strain energy at the TiN/NiO interface. We demonstrate a significantly enhanced long-range ordering of the core-shell nanopillars which enables a stronger Kerr anisotropy.