Magneto-optics of plasmonic nickel nanostructures

Mikko Kataja

Research output: ThesisDoctoral ThesisCollection of Articles

Abstract

Light can couple to subwavelength nanostructures via the excitation of surface plasmon polaritions. The rapid development of nanofabrication techniques has enabled significant advances in nanophotonics with plasmonics playing a key role. Combining extreme confinement of light in plasmonic nanostructures with active elements has opened up attractive prospects for controllable nanophotonic devices. Magneto-optically active materials are a potential candidate for such active elements as they enable non-reciprocal manipulation of the polarization characteristics of optical excitations and are easily and reversibly controlled by external magnetic fields. This thesis presents results on the magneto-optics and plasmonics of ferromagnetic nanostructures. The use of ferromagnetic nickel in subwavelength nanostructures offers a relatively simple geometry for an in-depth study on the relationship between plasmon excitations and magneto-optical activity. Experiments on circular nickel nanodots show that plasmon resonances correspond with a resonant enhancement of magneto-optically induced polarization rotation. Breaking the rotational symmetry in elliptical nanostructures demonstrates that the magneto-optical response can be described by excitation of two orthogonal electric dipole oscillations. Arranging the nanoparticles into a periodic lattice gives rise to more narrow and intense surface lattice resonances that, in turn, further enhance the magneto-optical activity at the resonance frequency. These properties arise from radiative coupling between the dipole oscillations of the individual nanoparticles. However, the optical and magneto-optical dipole resonances couple along orthogonal directions in the lattice, which enables active tuning of the magneto-optical response. Finally, it is shown that hybrid arrays of noble metal and ferromagnetic nanoparticles combine high optical reflectivity and strong magneto-optical activity. Radiative coupling between the sub-lattices of the hybrid array induces a collective magneto-optical response that involves both the magnetic and non-magnetic nanoparticles. The experimental results on single nickel nanoparticles are reproduced by an analytical model based on modified long wavelength approximation (MLWA) while the optical and magneto-optical response of periodic particle arrays are reproduced by a numerical model based on the discrete dipole approximation (DDA) that was expanded to include magneto-optical effects. The results on plasmonic nanostructures with integrated magneto-optical activity open up new avenues towards integrating magneto-optical elements into nanophotonic devices such as photonic crystals and metasurfaces.
Translated title of the contributionMagneto-optiset ilmiöt nikkeliplasmonirakenteissa
Original languageEnglish
QualificationDoctor's degree
Awarding Institution
  • Aalto University
Supervisors/Advisors
  • van Dijken, Sebastiaan, Supervising Professor
  • van Dijken, Sebastiaan, Thesis Advisor
Publisher
Print ISBNs978-952-60-6810-7
Electronic ISBNs978-952-60-6811-4
Publication statusPublished - 2016
MoE publication typeG5 Doctoral dissertation (article)

Keywords

  • nanotechnology
  • nanophotonics
  • plasmonics
  • magneto-optics
  • photonic crystals
  • surface plasmons

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