189 research outputs found
Infra-Red Surface-Plasmon-Resonance technique for biological studies
We report on a Surface-Plasmon-Resonance (SPR) technique based on Fourier
-Transform - Infra - Red (FTIR) spectrometer. In contrast to the conventional
surface plasmon technique, operating at a fixed wavelength and a variable angle
of incidence, our setup allows the wavelength and the angle of incidence to be
varied simultaneously. We explored the potential of the SPR technique in the
infrared for biological studies involving aqueous solutions. Using computer
simulations, we found the optimal combination of parameters (incident angle,
wavelength) for performing this task. Our experiments with physiologically
important glucose concentrations in water and in human plasma verified our
computer simulations. Importantly, we demonstrated that the sensitivity of the
SPR technique in the infrared range is not lower and in fact is even higher
than that for visible light. We emphasize the advantages of infra red SPR for
studying glucose and other biological molecules in living cells.Comment: 8 pages,8 figure
Low-field microwave absorption in epitaxial La-Sr-Mn-O films resulting from the angle-tuned ferromagnetic resonance in the multidomain state
We studied magnetic-field induced microwave absorption in 100-200 nm thick
LaSrMnO films on SrTiO substrate and found a
low-field absorption with a very peculiar angular dependence: it appears only
in the oblique field and is absent both in the parallel and in the
perpendicular orientations. We demonstrate that this low-field absorption
results from the ferromagnetic resonance in the multidomain state (domain-mode
resonance). Its unusual angular dependence arises from the interplay between
the parallel component of the magnetic field that drives the film into
multidomain state and the perpendicular field component that controls the
domain width through its effect on domain wall energy. The low-field microwave
absorption in the multidomain state can be a tool to probe domain structure in
magnetic films with in-plane magnetization.Comment: 9 pages, 9 Figure
Spin wave resonances in La_{0.7}Sr_{0.3}MnO_{3} films: measurement of spin wave stiffness and anisotropy field
We studied magnetic field dependent microwave absorption in epitaxial
LaSrMnO films using an X-band Bruker ESR spectrometer. By
analyzing angular and temperature dependence of the ferromagnetic and spin-wave
resonances we determine spin-wave stiffness and anisotropy field. The spin-wave
stiffness as found from the spectrum of the standing spin-wave resonances in
thin films is in fair agreement with the results of inelastic neutron
scattering studies on a single crystal of the same composition [Vasiliu-Doloc
et al., J. Appl. Phys. \textbf{83}, 7343 (1998)].Comment: 15 pages, 7 figures (now figure captions are included
Nonresonant microwave absorption in epitaxial La-Sr-Mn-O films and its relation to colossal magnetoresistance
We study magnetic-field-dependent nonresonant microwave absorption and
dispersion in thin LaSrMnO films and show that it
originates from the colossal magnetoresistance. We develop the model for
magnetoresistance of a thin ferromagnetic film in oblique magnetic field. The
model accounts fairly well for our experimental findings, as well as for
results of other researchers. We demonstrate that nonresonant microwave
absorption is a powerful technique that allows contactless measurement of
magnetic properties of thin films, including magnetoresistance, anisotropy
field and coercive field.Comment: 20 pages, 11 figure
Depinning frequency in a heavily neutron-irradiated MgB2 sample
The magnetic-field-induced variations of the microwave surface resistance
have been investigated in a heavily neutron-irradiated MgB2 sample, in which
the irradiation has caused the merging of the two gaps into a single value. The
experimental results have been analyzed in the framework of the Coffey and Clem
model. By fitting the experimental data, we have determined the field
dependence of the depinning frequency, omega_0, at different values of the
temperature. Although the pinning is not particularly effective, the value of
omega_0 obtained at low temperatures is considerably higher than that observed
in conventional low-temperature superconductors.Comment: 15 pages, 6 figures; to be published in Physica
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