| 1. |
- Mishra, K., et al.
(författare)
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Ultrafast Demagnetization Control in Magnetophotonic Surface Crystals
- 2022
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Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6984 .- 1530-6992. ; 22:23, s. 9773-80
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Tidskriftsartikel (refereegranskat)abstract
- Magnetic memory combining plasmonics and magnetism is poised to dramatically increase the bit density and energy efficiency of light-assisted ultrafast magnetic storage, thanks to nanoplasmon-driven enhancement and confinement of light. Here we devise a new path for that, simultaneously enabling light driven bit downscaling, reduction of the required energy for magnetic memory writing, and a subtle control over the degree of demagnetization in a magnetophotonic surface crystal. It features a regular array of truncated-nanocone-shaped Au-TbCo antennas showing both localized plasmon and surface lattice resonance modes. The ultrafast magnetization dynamics of the nanoantennas show a 3-fold resonant enhancement of the demagnetization efficiency. The degree of demagnetization is further tuned by activating surface lattice modes. This reveals a platform where ultrafast demagnetization is localized at the nanoscale and its extent can be controlled at will, rendering it multistate and potentially opening up so-far-unforeseen nanomagnetic neuromorphic-like systems operating at femtosecond time scales controlled by light.
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| 2. |
- Maccaferri, Nicolò, Dr. 1988-, et al.
(författare)
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Nanoscale magnetophotonics
- 2020
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 127:8
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Tidskriftsartikel (refereegranskat)abstract
- This Perspective surveys the state-of-the-art and future prospects of science and technology employing nanoconfined light (nanophotonics and nanoplasmonics) in combination with magnetism. We denote this field broadly as nanoscale magnetophotonics. We include a general introduction to the field and describe the emerging magneto-optical effects in magnetoplasmonic and magnetophotonic nanostructures supporting localized and propagating plasmons. Special attention is given to magnetoplasmonic crystals with transverse magnetization and the associated nanophotonic non-reciprocal effects and to magneto-optical effects in periodic arrays of nanostructures. We also give an overview of the applications of these systems in biological and chemical sensing, as well as in light polarization and phase control. We further review the area of nonlinear magnetophotonics, the semiconductor spin-plasmonics, and the general principles and applications of opto-magnetism and nano-optical ultrafast control of magnetism and spintronics. © 2020 Author(s).
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| 3. |
- Magnfält, Daniel, et al.
(författare)
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Synthesis of tunable plasmonic metal-ceramic nanocomposite thin films by temporally modulated sputtered fluxes
- 2017
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Ingår i: Journal of Applied Physics. - : AMER INST PHYSICS. - 0021-8979 .- 1089-7550. ; 121:17
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Tidskriftsartikel (refereegranskat)abstract
- The scientific and technological interest for metal-dielectric nanocomposite thin films emanates from the excitation of localized surface plasmon resonances (LSPRs) on the metal component. The overall optical response of the nanocomposite is governed by the refractive index of the dielectric matrix and the properties of the metallic nanoparticles in terms of their bulk optical properties, size, and shape, and the inter-particle distance of separation. In order to tune the film morphology and optical properties, complex synthesis processes which include multiple steps-i. e., film deposition followed by post-deposition treatment by thermal or laser annealing-are commonly employed. In the present study, we demonstrate that the absorption resonances of Ag/AlOxNy nanocomposite films can be effectively tuned from green (similar to 2.4 eV) to violet (similar to 2.8 eV) using a single-step synthesis process that is based on modulating the arrival pattern of film forming species with sub-monolayer resolution, while keeping the amount of Ag in the films constant. Our data indicate that the optical response of the films is the result of LSPRs on isolated Ag nanoparticles that are seemingly shifted by dipolar interactions between neighboring particles. The synthesis strategy presented may be of relevance for enabling integration of plasmonic nanocomposite films on thermally sensitive substrates. Published by AIP Publishing.
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| 4. |
- 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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| 5. |
- Novoselova, Iuliia P., et al.
(författare)
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Large uniaxial magnetostriction with sign inversion at the first order phase transition in the nanolaminated Mn2GaC MAX phase
- 2018
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Ingår i: Scientific Reports. - London : NATURE PUBLISHING GROUP. - 2045-2322. ; 8
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Tidskriftsartikel (refereegranskat)abstract
- In 2013, a new class of inherently nanolaminated magnetic materials, the so called magnetic MAX phases, was discovered. Following predictive material stability calculations, the hexagonal Mn2GaC compound was synthesized as hetero-epitaxial films containing Mn as the exclusive M-element. Recent theoretical and experimental studies suggested a high magnetic ordering temperature and non-collinear antiferromagnetic (AFM) spin states as a result of competitive ferromagnetic and antiferromagnetic exchange interactions. In order to assess the potential for practical applications of Mn2GaC, we have studied the temperature-dependent magnetization, and the magnetoresistive, magnetostrictive as well as magnetocaloric properties of the compound. The material exhibits two magnetic phase transitions. The Neel temperature is T-N similar to 507 K, at which the system changes from a collinear AFM state to the paramagnetic state. At T-t = 214 K the material undergoes a first order magnetic phase transition from AFM at higher temperature to a non-collinear AFM spin structure. Both states show large uniaxial c-axis magnetostriction of 450 ppm. Remarkably, the magnetostriction changes sign, being compressive (negative) above T-t and tensile (positive) below the T-t. The sign change of the magnetostriction is accompanied by a sign change in the magnetoresistance indicating a coupling among the spin, lattice and electrical transport properties.
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| 6. |
- Barnasas, A., et al.
(författare)
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Quantum confinement effects of thin ZnO films by experiment and theory
- 2020
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Ingår i: Physica. E, Low-Dimensional systems and nanostructures. - : ELSEVIER. - 1386-9477 .- 1873-1759. ; 120
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Tidskriftsartikel (refereegranskat)abstract
- Thin ZnO films with thickness ranging between 2 and 300 nm have been grown on quartz, Corning glass and Si (100) substrates by radio frequency magnetron sputtering. The film thickness was determined by pre-calibrated quartz balance with the help of x-ray reflectivity measurements. X-ray diffraction experiments revealed the formation of highly-textured hexagonal ZnO. Ultraviolet-visible light absorption spectroscopy has shown a "blue shift" of the direct band gap of ZnO. The experimental results are interpreted as evidences of quantum confinement effects. This is supported by theoretical predictions of the optical gap, which was calculated in the framework of effective mass approximation by solving the two particle (electron and hole) Hartree-Fock equations. The observed fair agreement between theoretical and experimental results corroborates the quantum confinement interpretation.
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| 7. |
- Gemma, Ryota, et al.
(författare)
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The impact of nanoscale compositional variation on the properties of amorphous alloys
- 2020
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Ingår i: Scientific Reports. - : NATURE PUBLISHING GROUP. - 2045-2322. ; 10:1
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Tidskriftsartikel (refereegranskat)abstract
- The atomic distribution in amorphous FeZr alloys is found to be close to random, nevertheless, the composition can not be viewed as being homogenous at the nm-scale. The spatial variation of the local composition is identified as the root of the unusual magnetic properties in amorphous Fe1-xZrx alloys. The findings are discussed and generalised with respect to the physical properties of amorphous and crystalline materials.
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| 8. |
- Melander, Emil, 1985-
(författare)
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Magnetoplasmonic nanostructures
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Surfaces that are nanopatterned, metallic, and magnetic can support surface plasmon resonances, providing an alternative and effective way to reconfigure flat optical components. Utilising a range of near- and far-field characterisation techniques, the optical and magneto-optical properties of lithographically patterned thin magnetic films are investigated.A magneto-optical diffractometer was designed, assembled, and commissioned to characterise periodic magneto-plasmonic nanostructures. For Ni and Co nanostructured antidot arrays, enhanced values of the magneto-optical Kerr rotation were recorded for energies and angles corresponding to excitations of surface plasmon polaritons. This enhancement was found to be thickness dependent. Modification of the optical properties via applied transverse magnetic fields and the excitation of surface plasmon polaritons, was demonstrated for an antidot array of pure Ni. The excitation was also shown to enhance the generation of second harmonics, as well as further activate nonlinear-optical mechanisms.In order to fully resolve and explain the source of this remarkable magneto-optical activity, near field probing techniques were used. This allows for mapping the electric near-field with a sub-wavelength resolution, thereby revealing the interplay between the light and the nanostructured lattice. The measurements show that the electric near field intensification, induced by plasmon excitation, increases the polarisation conversion, which correlates to the observed magneto-optical Kerr rotation.
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| 9. |
- Rowan-Robinson, Richard M., et al.
(författare)
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Direction-Sensitive Magnetophotonic Surface Crystals
- 2021
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Ingår i: Advanced Photonics Research. - : John Wiley & Sons. - 2699-9293. ; 2:10
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Tidskriftsartikel (refereegranskat)abstract
- Nanometer-thin rare-earth-€“transition-metal (RE-€“TM) alloys with precisely controlled compositions and out-of-plane magnetic anisotropy are currently in the focus for ultrafast magnetophotonic applications. However, achieving lateral nanoscale dimensions, crucial for potential device downscaling, while maintaining designable optomagnetic functionality and out-of-plane magnetic anisotropy is extremely challenging. Herein, nanosized Tb18Co82 ferrimagnetic alloys, having strong out-of-plane magnetic anisotropy, within a gold plasmonic nanoantenna array to design a micrometer-scale magnetophotonic crystal that exhibits abrupt and narrow magneto-optical (MO) spectral features that are both magnetic field and light incidence direction controlled are integrated. The narrow Fano-type resonance arises through the interference of the individual nanoantenna’s surface plasmons and a Rayleigh anomaly of the whole nanoantenna array, in both optical and MO spectra, which are demonstrated and explained using Maxwell theory simulations. This robust magnetophotonic crystal opens the way for conceptually new high-resolution light incidence direction sensors, as well as for building blocks for plasmon-assisted all-optical magnetization switching in ferrimagnetic RE-€“TM alloys.
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| 10. |
- Saini, Apurve
(författare)
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Magnetically governed self-assembly of soft matter : A look into interfacial layering, crystallization and percolation
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Self-organisation is the key route for assembling colloidal particles into well-defined structures. Decisive for this are the interactions between the constituents, which are amongst others steric, electrostatic or magnetic. A deep knowledge on the underlying physical processes during self-assembly is crucial for the design and fabrication of well-defined hierarchical architectures from a nanometer scale as well as for realizing smart, functional or stimuli responsive synthetic materials. In this dissertation, the self-assembly of colloidal magnetic particles into organized and multi-layered structures is studied. Particular emphasis is given to solid-liquid boundaries and the response to applied magnetic fields. Particle coatings with specific functional molecules stabilize the nanoparticles (NPs) in the solvent and can simultaneously promote their assembly at a substrate. An example in this context is N-hydroxysuccinimide interacting with (3-aminopropyl)triethoxy silane at the substrate. As a result of this chemical affinity, uniform and densely packed particle wetting layers are seeded which then instate the layering process. As an alternative to chemical binding, the magnetic stray field of a ferrimagnetic (Tb15Co85 film) deposited on a substrate induces particle self-assembly with dense layers as well. The application of an external magnetic field further promotes densification, particle layering and leads to variations in the assembly characteristics such as quasi-domain formation of closely packed layers. At an interface with a magnetic field applied in the plane of the interface, Brownian motion and Neel relaxation of the NPs are decisive for the layering and give raise to these domains. For a magnetic field oriented along the surface normal similar structural layering but denser packing is found. The self-assembly is a relatively slow process and evolves over hours and is maximized, most ordered and dense for superparamagnetic NPs which are single domain and having a large remanent moment and reduced thermal mobility. Small quantities of magnetic micelles in a hybrid magnetic polymer nanocomposite, facilitate the crystallization of Pluronic F127 micelles dissolved in water into single crystalline structures via a micro-shear effect under applied magnetic field. Also, a magnetic field applied to a colloidal dispersion of conducting magnetic and non-magnetic polystyrene microbeads suspended in an oil-based ferrofluid can lead to percolated structures. This allows current transmission and switching. A working contact for possible applications in automotive, switchboard and telecommunications is demonstrated.
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