131 research outputs found
Parametric frequency mixing in the magneto-elastically driven FMR-oscillator
We demonstrate the nonlinear frequency conversion of ferromagnetic resonance
(FMR) frequency by optically excited elastic waves in a thin metallic film on
dielectric substrates. Time-resolved probing of the magnetization directly
witnesses magneto-elastically driven second harmonic generation, sum- and
difference frequency mixing from two distinct frequencies, as well as
parametric downconversion of each individual drive frequency. Starting from the
Landau-Lifshitz-Gilbert equations, we derive an analytical equation of an
elastically driven nonlinear parametric oscillator and show that frequency
mixing is dominated by the parametric modulation of FMR frequency
Magneto-optical properties of Au upon the injection of hot spin-polarized electrons across Fe/Au(001) interfaces
We demonstrate a novel method for the excitation of sizable magneto-optical
effects in Au by means of the laser-induced injection of hot spin-polarized
electrons in Au/Fe/MgO(001) heterostructures. It is based on the energy- and
spin-dependent electron transmittance of Fe/Au interface which acts as a spin
filter for non-thermalized electrons optically excited in Fe. We show that
after crossing the interface, majority electrons propagate through the Au layer
with the velocity on the order of 1 nm/fs (close to the Fermi velocity) and the
decay length on the order of 100 nm. Featuring ultrafast functionality and
requiring no strong external magnetic fields, spin injection results in a
distinct magneto-optical response of Au. We develop a formalism based on the
phase of the transient complex MOKE response and demonstrate its robustness in
a plethora of experimental and theoretical MOKE studies on Au, including our ab
initio calculations. Our work introduces a flexible tool to manipulate
magneto-optical properties of metals on the femtosecond timescale that holds
high potential for active magneto-photonics, plasmonics, and spintronics
The effect of the complex processing of Microalgae Chlorella vulgaris on the intensification of the lipid extraction process
Microalgae are considered a promising source of lipids. However, the existing technologies of their extraction necessitate a massive improvement. In the course of the study optimal parameters of microwave radiation and of enzyme mixture "Cellolux A" and "Protosubtilin G3x" were experimentally selected and theoretically proved so as to allow increasing the yield of lipids 5.75 times to 23 % in comparison with the control sample (5 %). Moreover, the ratio and type of polar and non-polar solvents in the extraction stage for the maximum extraction of lipids was determined taking into account the necessity to process protein-lipid complexes
Femtosecond nonlinear ultrasonics in gold probed with ultrashort surface plasmons
Fundamental interactions induced by lattice vibrations on ultrafast time
scales become increasingly important for modern nanoscience and technology.
Experimental access to the physical properties of acoustic phonons in the THz
frequency range and over the entire Brillouin zone is crucial for understanding
electric and thermal transport in solids and their compounds. Here, we report
on the generation and nonlinear propagation of giant (1 percent) acoustic
strain pulses in hybrid gold/cobalt bilayer structures probed with ultrafast
surface plasmon interferometry. This new technique allows for unambiguous
characterization of arbitrary ultrafast acoustic transients. The giant acoustic
pulses experience substantial nonlinear reshaping already after a propagation
distance of 100 nm in a crystalline gold layer. Excellent agreement with the
Korteveg-de Vries model points to future quantitative nonlinear femtosecond
THz-ultrasonics at the nano-scale in metals at room temperature
Anatomy of ultrafast quantitative magneto-acoustics in freestanding nickel thin films
We revisit the quantitative analysis of the ultrafast magneto-acoustic
experiment in a freestanding nickel thin film by Kim and Bigot [1] by applying
our recently proposed approach of magnetic and acoustic eigenmodes
decomposition by Vernik et al. [2]. We show that the application of our
modeling to the analysis of time-resolved reflectivity measurements allows for
the determination of amplitudes and lifetimes of standing perpendicular
acoustic phonon resonances with unprecedented accuracy. The acoustic damping is
found to scale as for frequencies up to 80~GHz and the peak
amplitudes reach . The experimentally measured magnetization dynamics
for different orientations of an external magnetic field agrees well with
numerical solutions of magneto-elastically driven magnon harmonic oscillators.
Symmetry-based selection rules for magnon-phonon interactions predicted by our
modeling approach allow for the unambiguous discrimination between spatially
uniform and non-uniform modes, as confirmed by comparing the resonantly
enhanced magneto-elastic dynamics simultaneously measured on opposite sides of
the film. Moreover, the separation of time scales for (early) rising and (late)
decreasing precession amplitudes provide access to magnetic (Gilbert) and
acoustic damping parameters in a single measurement.Comment: 9 pages, 7 figure
Magnetoplasmonic design rules for active magneto-optics
Light polarization rotators and non-reciprocal 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
Terahertz spectroscopy for all-optical spintronic characterization of the spin-Hall-effect metals Pt, W and Cu80Ir20
Identifying materials with an efficient spin-to-charge conversion is crucial for future spintronic applications. In this respect, the spin Hall effect is a central mechanism as it allows for the interconversion of spin and charge currents. Spintronic material research aims at maximizing its efficiency, quantified by the spin Hall angle and the spin-current relaxation length . We develop an all-optical contact-free method with large sample throughput that allows us to extract and . Employing terahertz spectroscopy and an analytical model, magnetic metallic heterostructures involving Pt, W and Cu80Ir20 are characterized in terms of their optical and spintronic properties. The validity of our analytical model is confirmed by the good agreement with literature DC values. For the samples considered here, we find indications that the interface plays a minor role for the spin-current transmission. Our findings establish terahertz emission spectroscopy as a reliable tool complementing the spintronics workbench
Resonant phonon-magnon interactions in free-standing metal-ferromagnet multilayer structures
We analyze resonant magneto-elastic interactions between standing
perpendicular spin wave modes (exchange magnons) and longitudinal acoustic
phonon modes in free-standing hybrid metal-ferromagnet bilayer and trilayer
structures. Whereas the ferromagnetic layer acts as a magnetic cavity, all
metal layers control the frequencies and eigenmodes of acoustic vibrations. The
here proposed design allows for achieving and tuning the spectral and spatial
modes overlap between phonons and magnons that results in their strong resonant
interaction. Realistic simulations for gold-nickel multilayers show that
sweeping the external magnetic field should allow for observing resonantly
enhanced interactions between individual magnon and phonon modes in a broad
range of frequencies spanning from tens of GHz up to several hundreds of GHz,
which can be finely tuned through the multilayer design. Our results would
enable the systematic study and the deep understanding of resonantly enhanced
magneto-elastic coupling between individual phonon and magnon modes up to
frequencies of great contemporary fundamental and applied interest.Comment: 9 pages, 6 figure
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