Cross-Coupling of Periodic Resonances in a Two-Dimensional Magnetic Nanoparticle Array

Mikko Kataja Department of Applied physics, Aalto University, Espoo, Finland Tommi Hakala Department of Applied physics, Aalto University, Espoo, Finland Aleksi Julku Department of Applied physics, Aalto University, Espoo, Finland Mikko Huttunen Department of Applied physics, Aalto University, Espoo, Finland Sebastiaan van Dijken Department of Applied physics, Aalto University, Espoo, Finland Päivi Törmä Department of Applied physics, Aalto University, Espoo, Finland

Magneto-optical effects such as the Faraday and magneto-optical Kerr effect (MOKE) offer the ability to tune the optical response of magnetic materials via external magnetic fields, enabling their use in controllable plasmonic components. Recent studies have shown that the magneto-optical response of ferromagnetic nanoparticles is strongly influenced by localized surface plasmon resonances (LSPRs) [1] and that the magneto-optical response of a single ferromagnetic nanoparticle is governed by the LSPR polarized orthogonally to the driving field, creating a unique two-dimensional optical system [2].

Here, we explore the optical and magneto-optical response of a two-dimensional lattice of circular Ni nanoparticles (Figure 1a) [3]. We find that the optical response of ferromagnetic nanoparticle arrays show Fano-type surface lattice resonances (Figure 1b). We identify how the frequencies of the resonances depend on the lattice geometry and polarization. Our findings provide a new approach to control and enhance the magneto-optical Kerr response. The experimental results are reproduced by numerical calculations based on discrete dipole approximation (DDA) and an analytical model of coupled oscillators.

The narrow and intense magneto-optical resonances observed in our periodic arrays offer a novel way of offsetting damped optical resonances in ferromagnetic metals.

  1. Bonanni, S. Bonetti, T. Pakizeh et al., Nano Lett. 11, 5333 (2011)
  2. Maccaferri, A. Berger, S. Bonetti et al., Phys. Rev. Lett. 111, 167401 (2013)
  3. Kataja, T. K. Hakala, A. Julku, M. J. Huttunen, S. van Dijken and P. Törmä, Nat. Commun., in review (2014)

Figure 1

Figure 1: a) The incident electric field Ey induces a dipole dy in the plasmonic nanoparticle. The spin-orbit interaction induces an orthogonal dipole dx. b) Fourier space transmission spectrum of the nickel nanoparticle array

mikko.kataja@aalto.fi









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