474 research outputs found
Time-resolved magnetic field effect on triplet formation in photosynthetic reaction centers of rhodopseudomonas sphaeroides R-26
Ferromagnetic bubble clusters in YCaMnO thin films
We studied the ferromagnetic topology in a YCaMnO thin
film with a combination of magnetic force microscopy and magnetization
measurements. Our results show that the spin-glass like behavior, reported
previously for this system, could be attributed to frustrated interfaces of the
ferromagnetic clusters embedded in a non-ferromagnetic matrix. We found
temperature dependent changes of the magnetic topology at low temperatures,
which suggests a non-static Mn/Mn ratio
Recombination dynamics in bacterial photosynthetic reaction centers
The time dependence of magnetic field effects on light absorption by triplet-state and radical ions in quinone-depleted reaction centers of Rhodopseudomonas sphaeroides strain R-26 has been investigated. Measurements on the time scale of the hyperfine interaction in the radical pair [(BChl)2+. ...BPh-.)] provided kinetic data characterizing the recombination process. The results have been interpreted in terms of a recently proposed model that assumes an intermediate electron acceptor (close site) between the bacteriochlorophyll "special pair" (BChl)2 and the bacteriopheophytin BPh (distant site). Recombination is assumed to proceed through this intermediate acceptor. The experiments led to effective recombination rates for the singlet and triplet channel: k(Seff) = 3.9 . 107 s-1 and k(Teff) = 7.4 . 10(8) s-1. These correspond to recombination rates ks = 1 . 10(1) s-1 and kT = 7.1 . 10(11) s-1 in the close configuration. The upper bound of the effective spin dephasing rate k2eff approximately equal to 1 . 10(9) s-1 is identical with the rate of the electron hopping between the distant site of zero spin exchange interaction and the close site of large interaction. Interpretation of data for the case of direct recombination yields the recombination rates, spin dephasing rate, and exchange interaction in a straightforward way
Large magnetic penetration depth and thermal fluctuations in a Ca(PtAs)[(FePt)As] (x=0.097) single crystal
We have measured the temperature dependence of the absolute value of the
magnetic penetration depth in a
Ca(PtAs)[(FePt)As] (x=0.097)
single crystal using a low-temperature magnetic force microscope (MFM). We
obtain (0)1000 nm via extrapolating the data to .
This large and pronounced anisotropy in this system are responsible
for large thermal fluctuations and the presence of a liquid vortex phase in
this low-temperature superconductor with critical temperature of 11 K,
consistent with the interpretation of the electrical transport data. The
superconducting parameters obtained from and coherence length
place this compound in the extreme type \MakeUppercase{\romannumeral 2} regime.
Meissner responses (via MFM) at different locations across the sample are
similar to each other, indicating good homogeneity of the superconducting state
on a sub-micron scale
Pitfalls in the synthesis of nanoscaled perovskite type compounds, Part I: influence of different sol-gel preparation methods and characterization of nanoscaled BaTiO3
Different sol—gel routes are compared for the synthesis of nanoscaled BaTiO3 with respect to the reaction paths and the quality of the products. The various precursor systems differ largely in their behaviour during decomposition imposing quite different procedures for their thermal treatment. It is shown that the compositional homogeneity during the process of synthesis, which is the target of sol—gel methods, may well be destroyed by the formation of intermediate compounds. It will only be restored after prolonged heating at higher temperatures where the crystallite sizes will in general have left the nanoregime. Due to such pitfalls the desired properties of the products with narrow size distributions will not always be ensured when working according to such recipes and the products obtained will behave quite differently in fabrication procedures like shaping and sintering of workpieces
Strong magnetic field dependence of critical current densities and vortex activation energies in an anisotropic clean MgB2 thin film
We report the influence of two-band superconductivity on the flux creep and the critical current densities of a MgB2 thin film. The small magnetic penetration depth of lambda=50 +/- 10 nm at T=4 K is related to a clean pi-band. We find a high self-field critical current density J(C), which is strongly reduced with applied magnetic field, and attribute this to suppression of the superconductivity in the pi-band. The temperature dependence of the creep rate S (T) at low magnetic field can be explained by a simple Anderson-Kim mechanism. The system shows high pinning energies at low field that are strongly suppressed by high field. (C) 2014 Elsevier Ltd. All rights reserved.X1112Ysciescopu
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