Excitation of Ultrashort Spin Waves via Spin-Cherenkov Effect in Magnetic Waveguides

The excitation of ultrashort wavelength spin waves via the spin-Cherenkov effect in magnetic waveguides is investigated via a micromagnetic modeling. The proposed excitation method is relatively simple and easily tunable. The excitation efficiency of the proposed scheme is obtained for different excitation pulse velocities and widths. A coupled waveguide system is also considered. In this case, the spin waves are excited in the first waveguide and then are transferred to the second one due to the dipolar coupling between waveguides. It is also shown that the excitation and transfer of excited spin waves have some limitations related to the dipolar coupling mechanism between the waveguides.

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A Labile Metallo-Porphyrin as Tool to Control J-Aggregates Chiroptical Properties

10.32545/encyclopedia202006.0019.v16 ◽

2020 ◽

Author(s):

Luigi Monsù Scolaro ◽

Ilaria Occhiuto ◽

Mariachiara Trapani ◽

ROBERTO ZAGAMI ◽

Andrea Romeo ◽

...

Keyword(s):

Dipolar Coupling ◽

Initial Conditions ◽

Coupling Mechanism ◽

Precise Control ◽

Rate Determining Step ◽

Initial Nucleus ◽

Acidic Conditions ◽

J Aggregates ◽

Kinetics Of ◽

Autocatalytic Growth

The zinc(II) metal derivative of 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin (TPPS4) is quite labile and readily demetallates under acidic conditions, affording the parent diacid porphyrin in a monomeric form. The rate of this process is first order on [ZnTPPS4] and second order on [H+], allowing a precise control of the monomer release in solution. Under high ionic strength, this latter species is able to self-assemble into J-aggregates, whose kinetics of growth are largely modulated by pH. The aggregation kinetics have been treated according to a well-established model, in which the formation of an initial nucleus is the rate determining step preceding the autocatalytic growth of the whole assembly. The extinction spectra of the aggregates suggest the occurrence of a dipolar coupling mechanism very similar to that operating in metal nanoparticles. Spontaneous symmetry breaking takes place in these aggregates as evidenced by unusual circular dichroism spectra. The intensity and sign of the effect is controlled by the aggregation rate and therefore can be tuned through a proper choice of initial conditions.

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Efficiency improvement in the cantilever photothermal excitation method using a photothermal conversion layer

Beilstein Journal of Nanotechnology ◽

10.3762/bjnano.7.36 ◽

2016 ◽

Vol 7 ◽

pp. 409-417 ◽

Cited By ~ 2

Author(s):

Natsumi Inada ◽

Hitoshi Asakawa ◽

Taiki Kobayashi ◽

Takeshi Fukuma

Keyword(s):

Saline Solution ◽

Spring Constant ◽

Dynamic Mode ◽

Efficiency Improvement ◽

Colloidal Graphite ◽

Photothermal Conversion ◽

Excitation Efficiency ◽

Afm Imaging ◽

Fixed End ◽

Excitation Method

Photothermal excitation is a cantilever excitation method that enables stable and accurate operation for dynamic-mode AFM measurements. However, the low excitation efficiency of the method has often limited its application in practical studies. In this study, we propose a method for improving the photothermal excitation efficiency by coating cantilever backside surface near its fixed end with colloidal graphite as a photothermal conversion (PTC) layer. The excitation efficiency for a standard cantilever of PPP-NCHAuD with a spring constant of ≈40 N/m and a relatively stiff cantilever of AC55 with a spring constant of ≈140 N/m were improved by 6.1 times and 2.5 times, respectively, by coating with a PTC layer. We experimentally demonstrate high stability of the PTC layer in liquid by AFM imaging of a mica surface with atomic resolution in phosphate buffer saline solution for more than 2 h without any indication of possible contamination from the coating. The proposed method, using a PTC layer made of colloidal graphite, greatly enhances photothermal excitation efficiency even for a relatively stiff cantilever in liquid.

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Nanoscale magnonic Fabry-Pérot resonator for low-loss spin-wave manipulation

Nature Communications ◽

10.1038/s41467-021-22520-6 ◽

2021 ◽

Vol 12 (1) ◽

Author(s):

Huajun Qin ◽

Rasmus B. Holländer ◽

Lukáš Flajšman ◽

Felix Hermann ◽

Rouven Dreyer ◽

...

Keyword(s):

Spin Wave ◽

Dipolar Coupling ◽

Transmission Loss ◽

Spin Waves ◽

Wave Dispersion ◽

Material Structure ◽

Low Loss ◽

Device Structure ◽

Wave Transport ◽

Fabry Perot

AbstractActive control of propagating spin waves on the nanoscale is essential for beyond-CMOS magnonic computing. Here, we experimentally demonstrate reconfigurable spin-wave transport in a hybrid YIG-based material structure that operates as a Fabry-Pérot nanoresonator. The magnonic resonator is formed by a local frequency downshift of the spin-wave dispersion relation in a continuous YIG film caused by dynamic dipolar coupling to a ferromagnetic metal nanostripe. Drastic downscaling of the spin-wave wavelength within the bilayer region enables programmable control of propagating spin waves on a length scale that is only a fraction of their wavelength. Depending on the stripe width, the device structure offers full nonreciprocity, tunable spin-wave filtering, and nearly zero transmission loss at allowed frequencies. Our results provide a practical route for the implementation of low-loss YIG-based magnonic devices with controllable transport properties.

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