Magnetoplasmonics of ferromagnetic nanostructures

Plasmonics plays a key role in the development of advanced nanophotonics. Via the excitation of surface plasmons light can couple to subwavelength nanostructures. Active control of localized light opens up new avenues toward controllable nanophotonic devices. Magneto-optically active materials can introduce tunability and multifunctionality into passive plasmonic devices. In this thesis, the interaction between light and ferromagnetic nanostructures is investigated. In ferromagnetic nanoparticles that support the excitation of surface plasmons, spin-orbit coupling induces two electrical dipoles, one along the direction of the incident electric field and the second orthogonally to the first and the magnetization direction. The amplitude and phase relations of these two dipoles determine the magneto-optical response of the system upon transmission or reflection. Periodic arrangements of metal nanostructures lead to coupling between diffracted waves in the surface plane and localized surface plasmon resonances. The resulting surface lattice resonances enhance the magneto-optical signal of ferromagnetic systems. Further tailoring of the magneto-optical activity can be attained by combining ferromagnetic and noble metals. Two effects are studied here: Farfielddiffracted coupling between ferromagnetic and noble metal nanodisks in checkerboard arrays and vertical dimer structures that comprise ferromagnetic and noble metals within a single nanoparticle. If dimers are arranged into a periodic lattice, the magneto-optical response is resonantly enhanced by near- and farfield coupling between the two metals, a feature that is demonstrated to be attractive for high-resolution refractive index sensing. As a mechanism to overcome optical losses in magnetoplasmonic nanostructures, lasing in ferromagnetic nanoparticle arrays overlaid with an organic gain medium is demonstrated. The experimental results on magnetoplasmonic effects in ferromagnetic nanostructures arereproduced by models based on the modified long wavelength approximation (MLWA) and discrete dipole approximation (DDA).