Plasmon-induced demagnetization and magnetic switching in nickel nanoparticle arrays

Abstract

We report on the manipulation of magnetization by femtosecond laser pulses in a periodic array of cylindrical nickel nanoparticles. By performing experiments at different wavelength, we show that the excitation of collective surface plasmon resonances triggers demagnetization in zero field or magnetic switching in a small perpendicular field. Both magnetic effects are explained by plasmon-induced heating of the nickel nanoparticles to their Curie temperature. Model calculations confirm the strong correlation between the excitation of surface plasmon modes and laser-induced changes in magnetization.Plasmonic nanostructures enable strong local enhancements of the optical field in areas that are substantially smaller than the wavelength of incident light. This capability offers prospects for magnetic recording. In heat-assisted magnetic recording (HAMR), a plasmonic near-field transducer (NFT) reduces the switching field of high-anisotropy materials via local heating. 1-3 The NFT in this application is a noble metal nanostructure that is placed near the recording medium. Excitation of the NFT at the plasmon resonance frequency efficiently transfers optical energy to a nanoscale region, enabling local switching at reduced magnetic field. In the realm of ultrafast all-optical switching (AOS), 4,5 the use of noble metal plasmonic antennas has also been considered. By placing gold antennas on top of a ferrimagnetic TbFeCo film, Liu and co-workers demonstrated the confinement of magnetic switching to sub-100 nm length scales. 6 .Independent from HAMR and AOS, a new discipline combining plasmonics and magnetism has emerged recently. 7,8 Experiments on pure ferromagnetic metals demonstrate that, despite stronger ohmic damping, they also support surface plasmon resonances. [9][10][11] This raises the question if one could nanostructure the magnetic medium itself to trigger magnetic switching via local enhancements of the optical field. To study the effect of plasmon resonances on magnetic switching it is advantageous to consider ferromagnetic nanoparticles of uniform size and shape. In such nanoparticles, plasmon resonances determine the magneto-optical activity via the excitation of two orthogonal electric dipoles. 12 Plasmon resonances in single ferromagnetic nanoparticles are rather broad. Yet, ordering of the particles into a periodic array significantly narrows the spectral response. 13 In this geometry, hybridization between localized surface plasmons and the diffracted orders of the array produces intense surface lattice resonances (SLRs). SLR modes a) sebastiaan.van.dijken@aalto.fi and, thereby, the optical, magneto-optical, and magnetic circular dichroism (MCD) properties of a ferromagnetic nanoparticle array can be tuned by changing the period or symmetry of the lattice 13-15 or the shape of the nanoparticles. 16 These versatile designer tools could thus be exploited to spectrally gauge the significance of the inverse Faraday effect and MCD on all-optical switching in ferromagnetic materials, a topic of intense sc...

Coupling phenomena and collective effects in resonant meta-atoms supporting both plasmonic and (opto-)magnetic functionalities: an overview on properties and applications [Invited]

“…The combination of plasmon-induced heating by light with ferromagnetic nanoislands enables one to overcome limitations imposed by the grain size. Studies in this direction were also reported by Kataja et al [168], who reported on the manipulation of magnetization by femtosecond laser pulses in a periodic array of cylindrical nickel nanoparticles. They showed a strong correlation between the excitation of SLRs and changes in magnetization.…”

Nanoscale magnetophotonics

“…An X-ray diffraction study by Graves et al [224] on GdFeCo showed that a composition inhomogeneity could lead to local variations in the switching 51 behavior. A different investigation was made by Kataja et al [225], who could observe both plasmoninduced demagnetization and magnetic switching in a Ni nanoparticle array, excited by a femtosecond laser pulse, which they explained by the plasmonic local heating of the nanoparticles above the Curie temperature. A next step in this direction could be the fabrication of GdFeCo nanoparticle arrays.…”

Lasing in Ni Nanodisk Arrays

“…26 Potential applications of magnetoplasmonic nanostructures include nonreciprocal optical devices, 27 label-free biosensors, 28,29 metrology, 30 and ultrafast all-optical magnetic switching. 31 However, ohmic losses in ferromagnetic metals are considerably larger than those in noble metals, and the narrowing of intrinsically broad resonances via a transition to lasing has not been demonstrated yet.…”