| 1. |
- Fallarino, L., et al.
(författare)
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Magnetic properties of epitaxial CoCr films with depth-dependent exchange-coupling profiles
- 2017
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Ingår i: Physical Review B. - 2469-9950. ; 95:13
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Tidskriftsartikel (refereegranskat)abstract
- We present a study of the compositional and temperature-dependent magnetic properties of epitaxial CoCr thin films whose composition has a bathtublike depth profile Co/Co1 -> 1- xcCr0 -> xc/Co1-xcCrxc/Co1-xc -> 1Crxc -> 0/Co with the highest Cr concentration (x(c)) at the center of the sample. Polarized neutron reflectometry (PNR) shows that the effective Curie temperature varies as a function of depth and exhibits a minimum in the center of the structure. Correspondingly, we observe that the effective coupling between the two outer Co layers is strongly dependent on the magnetization of the graded CoCr spacer and can be continuously tuned via xc and temperature T. In particular, for x(c) = 0.28, magnetometry reveals a transition from one-step to two-step reversal behavior for temperatures T > 260 K, indicating a transition from a fully correlated magnetic film structure to an uncoupled system containing effectively two independent magnetic sublayers. Corroborating evidence of the temperature- dependent coupling of the top and bottom regions for x(c) = 0.28 was revealed by PNR, which demonstrated the field-dependent occurrence of antiparallel magnetization alignment on opposite interfaces at sufficiently high temperatures only.
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| 2. |
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| 3. |
- Lodewijks, Kristof, 1984, et al.
(författare)
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Magnetoplasmonic Design Rules for Active Magneto-Optics
- 2014
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Ingår i: Nano letters. - : American Chemical Society (ACS). - 1530-6984 .- 1530-6992. ; 14:12, s. 7207-7214
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Tidskriftsartikel (refereegranskat)abstract
- Light polarization rotators and nonreciprocal optical isolators are essential building blocks in photonics technology. These macroscopic passive devices are commonly based on magneto-optical Faraday and Kerr polarization rotation. Magnetoplasmonics, the combination of magnetism and plasmonics, is a promising route to bring these devices to the nanoscale. We introduce design rules for highly tunable active magnetoplasmonic elements in which we can tailor the amplitude and sign of the Kerr response over a broad spectral range.
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| 4. |
- Maccaferri, N., et al.
(författare)
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Tuning the Magneto-Optical Response of Nanosize Ferromagnetic Ni Disks Using the Phase of Localized Plasmons
- 2013
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 111:16
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Tidskriftsartikel (refereegranskat)abstract
- We explore the influence of the phase of localized plasmon resonances on the magneto-optical activity of nanoferromagnets. We demonstrate that these systems can be described as two orthogonal damped oscillators coupled by the spin-orbit interaction. We prove that only the spin-orbit induced transverse plasmon plays an active role on the magneto-optical properties by controlling the relative amplitude and phase lag between the two oscillators. Our theoretical predictions are fully confirmed by magneto-optical Kerr effect and optical extinction measurements in nanostructures of different size and shape.
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| 5. |
- Maccaferri, Nicolò, et al.
(författare)
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Ultrasensitive and label-free molecular-level detection enabled by light phase control in magnetoplasmonic nanoantennas
- 2015
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Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 6
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Tidskriftsartikel (refereegranskat)abstract
- Systems allowing label-free molecular detection are expected to have enormous impact on biochemical sciences. Research focuses on materials and technologies based on exploiting localized surface plasmon resonances in metallic nanostructures. The reason for this focused attention is their suitability for single-molecule sensing, arising from intrinsically nanoscopic sensing volume and the high sensitivity to the local environment. Here we propose an alternative route, which enables radically improved sensitivity compared with recently reported plasmon-based sensors. Such high sensitivity is achieved by exploiting the control of the phase of light in magnetoplasmonic nanoantennas. We demonstrate a manifold improvement of refractometric sensing figure-of-merit. Most remarkably, we show a raw surface sensitivity (that is, without applying fitting procedures) of two orders of magnitude higher than the current values reported for nanoplasmonic sensors. Such sensitivity corresponds to a mass of similar to 0.8 ag per nanoantenna of polyamide-6.6 (n = 1.51), which is representative for a large variety of polymers, peptides and proteins.
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| 6. |
- Mishra, K., et al.
(författare)
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Ultrafast demagnetization in a ferrimagnet under electromagnetic field funneling
- 2021
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Ingår i: Nanoscale. - : Royal Society of Chemistry (RSC). - 2040-3364 .- 2040-3372. ; 13:46, s. 19367-19375
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Tidskriftsartikel (refereegranskat)abstract
- The quest to improve the density, speed and energy efficiency of magnetic memory storage has led to the exploration of new ways of optically manipulating magnetism at the ultrafast time scale, in particular in ferrimagnetic alloys. While all-optical magnetization switching is well-established on the femtosecond timescale, lateral nanoscale confinement and thus the potential significant reduction of the size of the magnetic element remains an outstanding challenge. Here we employ resonant electromagnetic energy funneling through plasmon nanoantennas to influence the demagnetization dynamics of a ferrimagnetic TbCo alloy thin film. We demonstrate how Ag nanoring-shaped antennas under resonant optical femtosecond pumping reduce the overall demagnetization in the underlying films up to three times compared to non-resonant illumination. We attribute such a substantial reduction to the nanoscale confinement of the demagnetization process. This is qualitatively supported by the electromagnetic simulations that strongly evidence the resonant optical energy-funneling to the nanoscale from the nanoantennas into the ferrimagnetic film. This observation is an important step for reaching deterministic ultrafast all-optical magnetization switching at the nanoscale in such systems, opening a route to develop nanoscale ultrafast magneto-optics.
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| 7. |
- Unikandanunni, Vivek, 1993-, et al.
(författare)
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Ultrafast electron dynamics in platinum and gold thin films driven by optical and terahertz fields
- 2022
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 120:2
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Tidskriftsartikel (refereegranskat)abstract
- We investigate the ultrafast electron dynamics triggered by terahertz and optical pulses in thin platinum and gold films by probing their transient optical reflectivity. The response of the platinum film to an intense terahertz pulse is similar to the optically induced one and can be described by a two-temperature model with a 20% larger electron–phonon coupling for the terahertz-driven dynamics compared to the optically induced one, ascribed to an additional nonthermal electron–phonon coupling contribution. Surprisingly, gold films exhibit a much smaller terahertz pulse-induced reflectivity change and with a sign opposite to the optical case. We explain this remarkable observation with field emission of electrons due to Fowler–Nordheim tunneling, enabled in samples with thicknesses below the structural percolation threshold, where nanostructuring promotes near-field enhancement. Our results provide a fundamental insight into the ultrafast processes relevant to modern electro- and magneto-optical applications.
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| 8. |
- Verre, Ruggero, 1985, et al.
(författare)
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Polarization conversion-based molecular sensing using anisotropic plasmonic metasurfaces
- 2016
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Ingår i: Nanoscale. - : Royal Society of Chemistry. - 2040-3364 .- 2040-3372. ; 8:20, s. 10576-10581
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Tidskriftsartikel (refereegranskat)abstract
- Anisotropic media induce changes in the polarization state of transmitted and reflected light. Here we combine this effect with the refractive index sensitivity typical of plasmonic nanoparticles to experimentally demonstrate self-referenced single wavelength refractometric sensing based on polarization conversion. We fabricated anisotropic plasmonic metasurfaces composed of gold dimers and, as a proof of principle, measured the changes in the rotation of light polarization induced by biomolecular adsorption with a surface sensitivity of 0.2 ng cm(-2). We demonstrate the possibility of miniaturized sensing and we show that experimental results can be reproduced by analytical theory. Various ways to increase the sensitivity and applicability of the sensing scheme are discussed.
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