Metamaterial Platforms for Spintronic Modulation of Mid-Infrared Response under Very Weak Magnetic Field

Abstract

In this work, we experimentally demonstrate magnetic modulation of mid-infrared (mid-IR) plasmon resonances in microantenna and hole-array metamaterial platforms made of Ni81Fe19/Au multilayers. The responsible mechanism is the magnetorefractive effect linked to the giant magnetoresistance (GMR) present in this system. Ni81Fe19/Au multilayers experience a modification in the electrical resistivity upon the application of a small magnetic field. This directly translates into a change in the optical constants of the multilayer, making it possible to magnetically modulate the plasmon resonances. Because GMR acts on conduction electrons, the optical modulation occurs in the low energy, mid-IR range, even being possible to extend it to the THz range. Electrodynamical calculations confirm the experimental observations. This approach improves by up to 2 orders of magnitude previous attempts for mid-IR magnetic modulation, is potentially ultrafast due to the characteristic spintronics dynamics, and establishes a roadmap for spintronically controlled devices in the whole mid-IR to THz band.

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

“…Indeed, one of the missing pieces of this intricated puzzle is a systematic exploration of the fundamental properties of magneto-plasmonic metamaterials between the visible/near-infrared and the THz regions. Nevertheless, an interesting approach has been recently proposed to manipulate spin currents using mid-IR plasmons in magnetic microantenna and hole-array metamaterial platforms made of Ni81Fe19/Au multilayers, where the magneto-refractive effect linked to the giant magnetoresistance (GMR) present in the system allows a modification of the electrical resistivity upon the application of a small magnetic field [217]. This research field is still quite unexplored and might represent the point of contact between optics and magnetism at which the community as looked at so far.…”

Active photonic platforms for the mid-infrared to the THz regime using spintronic structures

“…Different aspects have actually been considered, such as the magnetic modulation of propagating and localized plasmons, or how the shape and size of the nanostructures affect their performance. In this line, in Figure 10 we show the first example, consisting of an ordered array of circular micrometric holes in an extraordinary optical transmission like fashion fabricated in a Ni 81 Fe 19 /Au GMR multilayer [101]. The ordering and lattice parameter of the array of the holes makes possible the excitation of propagating plasmon polaritons at the desired wavelength.…”

“…For example, 4% GMR is achieved for 2.3 nm Au spacer thickness, while it vanishes for 1.9 and 2.6 nm [61]. Based on Ni 81 Fe 19 /Au multilayers, magnetic field control of the mid IR response in a variety of metastructures has recently been demonstrated, with predicted perspectives of continuous increased modulation for longer wavelengths [100][101][102]. Different aspects have actually been considered, such as the magnetic modulation of propagating and localized plasmons, or how the shape and size of the nanostructures affect their performance.…”

“…As it can be seen, the transmission spectra for the two samples with identical periodicity and just slightly different amount of Au was basically the same, while the multilayer patterned with a different periodicity shows a similar spectral structure but with the peaks shifted. A more systematic analysis [101] reveals the dispersive nature of the excited modes. The results on the magnetic field modulation in these structures are shown in Figure 10 B.…”

Broad band infrared modulation using spintronic-plasmonic metasurfaces

“…This change in the permittivity can be exploited, among other uses, for increasing the sensitivity of optical sensors [12][13][14][15], creating switching mono/bi-directional devices [16,17] or fabricating other active infrared devices [18][19][20]. Recently, the family of the giant magnetoresistance (GMR) materials is incorporated into the list of active-control opportunities, demonstrating modulation of mid-infrared response in spintronic-plasmonic platforms using very low magnetic fields [21,22]. This new approach exploits the spin character of the conduction electrons via the spin-dependent electron transport properties of GMR metallic multilayers [23][24][25], merging, as a result, spintronic and plasmonics.…”