35 research outputs found
Polymer Brushes in Cylindrical Pores: Simulation versus Scaling Theory
The structure of flexible polymers endgrafted in cylindrical pores of
diameter D is studied as a function of chain length N and grafting density
\sigma, assuming good solvent conditions. A phenomenological scaling theory,
describing the variation of the linear dimensions of the chains with \sigma, is
developed and tested by Molecular Dynamics simulations of a bead-spring model.Comment: 35 pages, 38 figure
Phase diagrams of classical spin fluids: the influence of an external magnetic field on the liquid-gas transition
The influence of an external magnetic field on the liquid-gas phase
transition in Ising, XY, and Heisenberg spin fluid models is studied using a
modified mean field theory and Gibbs ensemble Monte Carlo simulations. It is
demonstrated that the theory is able to reproduce quantitatively all
characteristic features of the field dependence of the critical temperature
T_c(H) for all the three models. These features include a monotonic decrease of
T_c with rising H in the case of the Ising fluid as well as a more complicated
nonmonotonic behavior for the XY and Heisenberg models. The nonmonotonicity
consists in a decrease of T_c with increasing H at weak external fields, an
increase of T_c with rising H in the strong field regime, and the existence of
a minimum in T_c(H) at intermediate values of H. Analytical expressions for
T_c(H) in the large field limit are presented as well. The magnetic para-ferro
phase transition is also considered in simulations and described within the
mean field theory.Comment: 14 pages, 12 figures (to be submitted to Phys. Rev. E
Terahertz Spectroscopy Based on Josephson High-Temperature Superconductor Junctions
A review of the authors' studies on the spectroscopy employing the ac Josephson effect in high-temperature superconducting junctions is presented. It is demonstrated that Hilbert spectroscopy and admittance spectroscopy can be successfully implemented in the terahertz frequency range with the use of high-temperature superconductor bicrystal Josephson junctions
Acoustic spin pumping in magnetoelectric bulk acoustic wave resonator
We present the generation and detection of spin currents by using magnetoelastic resonance excitation in a magnetoelectric composite high overtone bulk acoustic wave (BAW) resonator (HBAR) formed by a Al-ZnO-Al-GGG-YIG-Pt structure. Transversal BAW drives magnetization oscillations in YIG film at a given resonant magnetic field, and the resonant magneto-elastic coupling establishes the spin-current generation at the Pt/YIG interface. Due to the inverse spin Hall effect (ISHE) this BAW-driven spin current is converted to a dc voltage in the Pt layer. The dependence of the measured voltage both on magnetic field and frequency has a resonant character. The voltage is determined by the acoustic power in HBAR and changes its sign upon magnetic field reversal. We compare the experimentally observed amplitudes of the ISHE electrical field achieved by our method and other approaches to spin current generation that use surface acoustic waves and microwave resonators for ferromagnetic resonance excitation, with the theoretically expected values