Orographic Disturbances of Upper Atmosphere Emissions

There are some increases of the temperature of the hydroxyl emission (delta T approximately 20 K, z approximately 90 km) and of the intensity of the 63000 oxygen emission (delta I/I approximately 20 per cent, z approximately 250 km) for the lee of the mountains at distances about 150 km in the case of the latitudinal direction of the wind (U approximately 10 m/s) at the 3000 m level. Airflow motions over mountains may be one of the possible processes of generation of wave disturbances penetrating into the upper atmospheres (HINES, 1974; LINDZEN, 1971). The purpose here is to study the penetration of orographic disturbances into upper atmosphere. Airplane measurements of emission variations of hydroxyl and atomic oxygen 6300 A near the Northern Ural mountains were made. Several nocturnal flights were carried out in March, 1980 and January to February, 1981 at heights about 3000 m along 64 deg northern latitude in the Ural region. Spectrographs SP-48 with electronic image converters registration for OH ((9,4) and (5,1) bands - 7700 to 8100 A) and OI (6300 A) emissions were used. The zenith region was observed, and exposure time was 2 minutes. This corresponds to averaging of the emission intensities along the airplane trace over a distance of 10 km. Simultaneous measurements of atmospheric temperature variations at the flight altitude were made

Strong enhancement of direct magnetoelectric effect in strained ferroelectric-ferromagnetic thin-film heterostructures

The direct magnetoelectric (ME) effect resulting from the polarization changes induced in a ferroelectric film by the application of a magnetic field to a ferromagnetic substrate is described using the nonlinear thermodynamic theory. It is shown that the ME response strongly depends on the initial strain state of the film. The ME polarization coefficient of the heterostructures involving Terfenol-D substrates and compressively strained lead zirconate titanate (PZT) films, which stabilize in the out-of-plane polarization state, is found to be comparable to that of bulk PZT/Terfenol-D laminate composites. At the same time, the ME voltage coefficient reaches a giant value of 50 V/(cm Oe), which greatly exceeds the maximum observed static ME coefficients of bulk composites. This remarkable feature is explained by a favorable combination of considerable strain sensitivity of polarization and a low electric permittivity in compressively strained PZT films. The theory also predicts a further dramatic increase of ME coefficients at the strain-induced transitions between different ferroelectric phases.Comment: 7 pages, 3 figure

Thermodynamic theory of epitaxial ferroelectric thin films with dense domain structures

A Landau-Ginsburg-Devonshire-type nonlinear phenomenological theory is presented, which enables the thermodynamic description of dense laminar polydomain states in epitaxial ferroelectric thin films. The theory explicitly takes into account the mechanical substrate effect on the polarizations and lattice strains in dissimilar elastic domains (twins). Numerical calculations are performed for PbTiO3 and BaTiO3 films grown on (001)-oriented cubic substrates. The "misfit strain-temperature" phase diagrams are developed for these films, showing stability ranges of various possible polydomain and single-domain states. Three types of polarization instabilities are revealed for polydomain epitaxial ferroelectric films, which may lead to the formation of new polydomain states forbidden in bulk crystals. The total dielectric and piezoelectric small-signal responses of polydomain films are calculated, resulting from both the volume and domain-wall contributions. For BaTiO3 films, strong dielectric anomalies are predicted at room temperature near special values of the misfit strain.Comment: 19 pages, 8 figure

Soft modes of collective domain-wall vibrations in epitaxial ferroelectric thin films

Mechanical restoring forces acting on ferroelastic domain walls displaced from the equilibrium positions in epitaxial films are calculated for various modes of their cooperative translational oscillations. For vibrations of the domain-wall superlattice with the wave vectors corresponding to the center and boundaries of the first Brillouin zone, the soft modes are singled out that are distinguished by a minimum magnitude of the restoring force. It is shown that, in polydomain ferroelectric thin films, the soft modes of wall vibrations may create enormously large contribution to the film permittivity.Comment: 6 pages, 3 figure

Creep motion of a domain wall in the two-dimensional random-field Ising model with a driving field

With Monte Carlo simulations, we study the creep motion of a domain wall in the two-dimensional random-field Ising model with a driving field. We observe the nonlinear fieldvelocity relation, and determine the creep exponent {\mu}. To further investigate the universality class of the creep motion, we also measure the roughness exponent {\zeta} and energy barrier exponent {\psi} from the zero-field relaxation process. We find that all the exponents depend on the strength of disorder.Comment: 5 pages, 4 figure