3,127 research outputs found
Optimality Criterion for Singular Controllers: Linear Boundary Conditions
AbstractThis paper is concerned with the dynamic process governed by the boundary value problem. We examine the situation with the appearance of singular controllers and formulate a second-order optimality criterion on the basis of the increment formula. We also show how to apply this criterion as a verifying condition for optimality and how to perform an optimal design for a singular controller
Magnon-magnon coupling in synthetic ferrimagnets
Magnetic multilayers with interlayer exchange coupling have been widely
studied for both static and dynamic regimes. Their dynamical responses depend
on the exchange coupling strength and magnetic properties of individual layers.
Magnetic resonance spectra in such systems are conveniently discussed in terms
of coupling of acoustic and optical modes. At a certain value of applied
magnetic field, the two modes come close to being degenerate and the spectral
gap indicates the strength of mode hybridisation. In this work, we
theoretically and experimentally study the mode hybridisation of
interlayer-exchange-coupled moments with dissimilar magnetisation and thickness
of two ferromagnetic layers. In agreement with symmetry analysis for
eigenmodes, our low-symmetry multilayers exhibit sizable spectral gaps for all
experimental conditions. The spectra agree well with the predictions from the
Landau-Lifshitz-Gilbert equation at the macrospin limit whose parameters are
independently fixed by static measurements.Comment: 13 pages, 13 figure
Strong suppression of superconductivity by divalent Ytterbium Kondo-holes in CeCoIn_5
To study the nature of partially substituted Yb-ions in a Ce-based Kondo
lattice, we fabricated high quality Ce_{1-x}Yb_xCoIn_5 epitaxial thin films
using molecular beam epitaxy. We find that the Yb-substitution leads to a
linear decrease of the unit cell volume, indicating that Yb-ions are divalent
forming Kondo-holes in Ce_{1-x}Yb_xCoIn_5, and leads to a strong suppression of
the superconductivity and Kondo coherence. These results, combined with the
measurements of Hall effect, indicate that Yb-ions act as nonmagnetic impurity
scatters in the coherent Kondo lattice without serious suppression of the
antiferromagnetic fluctuations. These are in stark contrast to previous studies
performed using bulk single crystals, which claim the importance of valence
fluctuations of Yb-ions. The present work also highlights the suitability of
epitaxial films in the study of the impurity effect on the Kondo lattice.Comment: 5 pages, 4 figure
Electrical detection of spin pumping: dc voltage generated by ferromagnetic resonance at ferromagnet/nonmagnet contact
We describe electrical detection of spin pumping in metallic nanostructures.
In the spin pumping effect, a precessing ferromagnet attached to a normal-metal
acts as a pump of spin-polarized current, giving rise to a spin accumulation.
The resulting spin accumulation induces a backflow of spin current into the
ferromagnet and generates a dc voltage due to the spin dependent conductivities
of the ferromagnet. The magnitude of such voltage is proportional to the
spin-relaxation properties of the normal-metal. By using platinum as a contact
material we observe, in agreement with theory, that the voltage is
significantly reduced as compared to the case when aluminum was used.
Furtheremore, the effects of rectification between the circulating rf currents
and the magnetization precession of the ferromagnet are examined. Most
significantly, we show that using an improved layout device geometry these
effects can be minimized.Comment: 9 pages, 11 figure
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