471 research outputs found
Influence of external factors on dielectric permittivity of Rochelle salt: humidity, annealing, stresses, electric field
The present work contains results of experimental investigation of external
factors, such as dessicating/wetting, thermal annealing, uniaxial and
hydrostatic pressures on dielectric permittivity of Rochelle salt crystals. The
obtained results are compared with available literature data. A conslusion is
made that the dispersion of experimental data can be attributed to internal
polar point defects in crystals and to influence of storage conditions. The
obtained results are analyzed within the phenomenological Landau approach
Liquid phase epitaxy and optical investigation of KYb(WO4)2 thin layers
In recent years, Yb3+ has attracted much attention as an activating ion because of its small quantum defect for laser emission from 2F5/2 to 2F7/2 at ~1.03 µm [1], which provides high efficiency and reduced heat generation. Of high practical interest is the thin-disk laser concept [2], which possesses a tremendous advantage over rod lasers because of its axial-cooling approach and consequent weak thermal lensing and good beam quality.\ud
A promising material for Yb3+ thin-disk lasers is KYb(WO4)2 (KYbW) [3]. It can be grown from high-temperature solutions [4]. Nevertheless, the growth of high-quality, single-crystalline layers with thickness in the range of the absorption length of ~13 µm at 981 nm has as yet not been reported. A suitable substrate material is KY(WO4)2 (KYW), but the relatively large differences in the thermal expansion coefficients between KYW and KYbW along the [100], [001], and especially [010] directions [5] favor low temperatures for the hetero-epitaxial growth.\ud
For the first time, we demonstrate liquid phase epitaxy (LPE) of KYbW layers. The layers were grown at start temperatures as low as 520°C, which is favorable in order to decrease the thermal stresses due to the differences in the thermal expansion coefficients of substrate and layer. Moreover, the choice of [010]-oriented substrates bypasses the large difference in the thermal expansion coefficient along the [010] direction. KY1-xYbx(WO4)2 layers with varying x = 0.03-1.00 were grown by LPE. The chloride solvent consisted of the eutectic composition [6] 24.4 mol.% KCl, 30.4 mol.% NaCl, and 42.2 mol.% CsCl. The growth temperature spanned the range from 580 to 500°C and the cooling rate was 0.67-1.00 Kh-1. Crack-free, transparent KYbW layers were grown on (010) substrates.\ud
Spectroscopic investigations have shown that the lifetime of ~250 µs measured in our LPE-grown KYbW layers is dominated by radiative decay and is very similar to that measured in top-seeded-solution-grown bulk samples [4]. Fast energy migration among the Yb3+ ions and energy transfer to small amounts of Tm3+ and Er3+ ions present in the YbCl3 reagent lead to visible upconversion luminescence in the layers under 981-nm excitation.\ud
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[1] T.Y. Fan, IEEE J. Quantum Electron. 29, 1457 (1993).\ud
[2] A. Giesen, H. Hügel, A. Voss, K. Wittig, U. Brauch, H. Opower, Appl. Phys. B 58, 365 (1994).\ud
[3] P. Klopp, U. Griebner, V. Petrov, X. Mateos, M.A. Bursukova, M.C. Pujol, R. Solé, J. Gavaldà, M. Aguiló, F. Güell, J. Massons, T. Kirilov, F. Díaz, Appl. Phys. B 74, 185 (2002).\ud
[4] M.C. Pujol, M.A. Bursukova, F. Güell, X. Mateos, R. Solé, J. Gavaldà, M. Aguiló, J. Massons, F. Díaz, P. Klopp, U. Griebner, V. Petrov, Phys. Rev. B 65, 165121 (2002).\ud
[5] M.C. Pujol, X. Mateos, R. Solé, J. Massons, J. Gavaldà, F. Díaz, M. Aguiló, Mater. Sci. Forum 378-381, 710 (2001).\ud
[6] D. Ehrentraut, M. Pollnau, S. Kück, Appl. Phys. B 75, 59 (2002)
Liquid phase epitaxy and spectroscopic investigation of optically active KYb(WO4)2 thin layers
In recent years, Yb3+ has attracted much attention as an activating ion because of its small quantum defect for laser emission from 2F5/2 to 2F7/2 at ~1.03 µm, which provides high efficiency and reduced heat generation. A promising material for Yb3+ lasers is KYb(WO4)2 (KYbW) [1]. It can be grown from high-temperature solutions [2]. A suitable substrate material for the growth of single-crystalline layers with thicknesses in the range of the absorption length of ~13 µm at 981 nm is KY(WO4)2 (KYW).\ud
We demonstrate the liquid phase epitaxy (LPE) of KYbW layers at start temperatures as low as 520°C from the chloride solvent KCl-NaCl-CsCl. This temperature is favorable in order to decrease the thermal stresses due to the differences in the thermal expansion coefficients of substrate and layer. Moreover, the choice of [010]-oriented KYW substrates bypasses the large difference in the thermal expansion coefficient along the [010] direction. Our spectroscopic investigations show that the fluorescence lifetime of ~250 µs measured in our LPE-grown KYbW layers is dominated by radiative decay and is very similar to that measured in top-seeded-solution-grown bulk samples [2]. Fast energy migration among the Yb3+ ions and energy transfer to small amounts of Tm3+ and Er3+ ions present in the YbCl3 reagent lead to visible upconversion luminescence in the layers under 981-nm excitation.\ud
\ud
[1] P. Klopp, U. Griebner, V. Petrov, X. Mateos, M.A. Bursukova, M.C. Pujol, R. Solé, J. Gavaldà, M. Aguiló, F. Güell, J. Massons, T. Kirilov, F. Díaz, Appl. Phys. B 2002, 74, 185\ud
[2] M.C. Pujol, M.A. Bursukova, F. Güell, X. Mateos, R. Solé, J. Gavaldà, M. Aguiló, J. Massons, F. Díaz, P. Klopp, U. Griebner, V. Petrov, Phys. Rev. B 2002, 65, 16512
Temperature dependent relaxation of dipole-exchange magnons in yttrium iron garnet films
Low energy consumption enabled by charge-free information transport, which is
free from ohmic heating, and the ability to process phase-encoded data by
nanometer-sized interference devices at GHz and THz frequencies are just a few
benefits of spin-wave-based technologies. Moreover, when approaching cryogenic
temperatures, quantum phenomena in spin-wave systems pave the path towards
quantum information processing. In view of these applications, the lifetime of
magnonsspin-wave quantais of high relevance for the fields of magnonics,
magnon spintronics and quantum computing. Here, the relaxation behavior of
parametrically excited magnons having wavenumbers from zero up to was experimentally investigated in the temperature range
from 20 K to 340 K in single crystal yttrium iron garnet (YIG) films
epitaxially grown on gallium gadolinium garnet (GGG) substrates as well as in a
bulk YIG crystalthe magnonic materials featuring the lowest magnetic damping
known so far. As opposed to the bulk YIG crystal in YIG films we have found a
significant increase in the magnon relaxation rate below 150 Kup to 10.5
times the reference value at 340 Kin the entire range of probed wavenumbers.
This increase is associated with rare-earth impurities contaminating the YIG
samples with a slight contribution caused by coupling of spin waves to the spin
system of the paramagnetic GGG substrate at the lowest temperatures
Cyber security and data privacy
The importance of cyber security and data privacy is described in the paper. Common threats to computer systems and ways how to minimise risks are mentioned. Worldwide Data Privacy Regulations are presented
The variation of the magnetic field of the Ap star HD~50169 over its 29 year rotation period
Context. The Ap stars that rotate extremely slowly, with periods of decades
to centuries, represent one of the keys to the understanding of the processes
leading to the differentiation of stellar rotation.
Aims. We characterise the variations of the magnetic field of the Ap star HD
50169 and derive constraints about its structure.
Methods. We combine published measurements of the mean longitudinal field
of HD 50169 with new determinations of this field moment from circular
spectropolarimetry obtained at the 6-m telescope BTA of the Special
Astrophysical Observatory of the Russian Academy of Sciences. For the mean
magnetic field modulus , literature data are complemented by the analysis of
ESO spectra, both newly acquired and from the archive. Radial velocities are
also obtained from these spectra.
Results. We present the first determination of the rotation period of HD
50169, Prot = (29.04+/-0.82) y. HD 50169 is currently the longest-period Ap
star for which magnetic field measurements have been obtained over more than a
full cycle. The variation curves of both and have a significant degree
of anharmonicity, and there is a definite phase shift between their respective
extrema. We confirm that HD 50169 is a wide spectroscopic binary, refine its
orbital elements, and suggest that the secondary is probably a dwarf star of
spectral type M.
Conclusions. The shapes and mutual phase shifts of the derived magnetic
variation curves unquestionably indicate that the magnetic field of HD 50169 is
not symmetric about an axis passing through its centre. Overall, HD 50169
appears similar to the bulk of the long-period Ap stars.Comment: 10 pages, 3 figures, accepted for publication in A&
Why such a tool as a mobile app is important for ebusiness?
The role of mobile apps for e-business is considered. Websites and mobile applications are compared. Companies’ performance and their progress in relation to mobile apps is discussed
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