Memory effects in permalloy-niobium hybrid structures

The kineticts of magnetization reversal of stripe-shaped permalloy-niobium hybrid nanofilms is studied in 6-300 K temperature range by means of magneto-optics visualization technique. The niobium influence on magnetic domain walls type and on magnetic domain structure of permalloy via the interface quality and via the distortion of stray fields is found. The memory effect, which is the superconducting niobium memory about an initial magnetic domain structure of permalloy at cooling below T_c, is found. The memory is razed only by hybrid heating over T_c

Current and field stimulated motion of domain wall in narrow permalloy stripe

Of the new types of cryoelectronic devices under development, including phase shifters, giant magnetoresistance switches, diodes, transistors, and memory cells, some are based on hybrid superconductor-normal metal or superconductor-ferromagnet films. Control of these devices is realized by means of pulses of voltage, light, or magnetic field. Spin-polarized current may be used to switch low-temperature devices, as in spin-electronic devices. In the superconducting layer, the current is dissipation less, which would bring large reduction of energy consumption. We demonstrate that mag-netic domain walls in bilayer niobium-permalloy stripes are shifted by electrical current along the stripe even at low tem-perature, with the niobium in the superconducting state. The wall motion in response to current pulses is quite different from that induced by a magnetic field pulses only. The effect could be used to create a new type of sequentially switched serial devices because of very high value of the wall velocity, which excides by many orders of magnitude the velocity of the wall moved with magnetic field pulses.Comment: 5 pages, 6 figure

Search for gas accretion imprints in voids: I. Sample selection and results for NGC 428

We present the first results of a project aimed at searching for gas accretion events and interactions between late-type galaxies in the void environment. The project is based on long-slit spectroscopic and scanning Fabry-Perot interferometer observations performed with the SCORPIO and SCORPIO-2 multimode instruments at the Russian 6-m telescope, as well as archival multiwavelength photometric data. In the first paper of the series we describe the project and present a sample of 18 void galaxies with oxygen abundances that fall below the reference `metallicity-luminosity' relation, or with possible signs of recent external accretion in their optical morphology. To demonstrate our approach, we considered the brightest sample galaxy NGC 428, a late-type barred spiral with several morphological peculiarities. We analysed the radial metallicity distribution, the ionized gas line-of-sight velocity and velocity dispersion maps together with WISE and SDSS images. Despite its very perturbed morphology, the velocity field of ionized gas in NGC 428 is well described by pure circular rotation in a thin flat disc with streaming motions in the central bar. We also found some local non-circular gas motions clearly related to stellar feedback processes. At the same time, we revealed a circumnuclear inclined disc in NGC 428 and a region with significant residual velocities that could be considered as a result of a recent (<0.5 Gyr) accretion event. The observed oxygen abundance gradient does not contradict this conclusion.Comment: Accepted for publication in MNRAS; 13 pages, 10 figures, 4 table

SDSS J170745+302056: a low surface brightness galaxy in a group

On the basis of the SDSS survey and spectral observations with the 6-m telescope of SAO RAS, we have peformed a detailed study of SDSS J170745+302056. By combination of its characteristics -- exponential surface brightness distribution, central surface brightness of stellar disk \mu_0(B) = 23.25\,^m/\square", blue colors, low metallicity and low star formation rate -- the galaxy is a typical low surface brightness spiral galaxy. Exponential scalelength of the galaxy is $\approx$3 kpc, its optical diameter exceeds 20 kpc. SDSS J170745+302056 is a member of a group of five galaxies and probably it is in interaction with UGC 10716. The existence of a large low surface brightness galaxy in such a dense environment is very unusual.Comment: 8 pages, 4 figure

Kinematics of CMEs and associated shock waves as deduced from LASCO data: comparative analysis

From data by LASCO C2 and C3 coronagraphs, depending on time (distance), we have determined positions and velocities of the front for fast limb CMEs' body with their sources near the limb, and for the body of halo-type CME with the sources near the solar disk center. These characteristics of CME body are compared to similar kinematic characteristics obtained for CME body-associated shock waves (shocks). For the body of halo-type CME with the sources near the solar disk center and associated shocks, we determined and compared their kinematic characteristics in 3D space. It has been shown that for all the considered CME groups, the shock velocity is higher than the CME body velocity, both velocities decrease as the mass ejection moves. As this takes place, the distance between CME body and shock grows. On average, distance from CME body to shock, and velocity difference of these structures is greater for a halo CME, and even greater for a model CME in 3D

With no Color and Scent (part II): Metal and Alloy Microstructures-Handmade Replicas of Natural Objects

As a continuation of work on metal and alloy "plants" synthesis on porous membranes by means of pulsed current electroplating volume metallic microstructures resembling such natural objects as shells, cabbage leaves, mushrooms are grown and presented in their modest elegance. Such structures are formed from PdNi and PdCo alloys as well as Ag, Cu and Ni in conditions defined by the shape of membrane pores and the parameters of the pulsed current. It is shown that the obtained complex structures are formed by layers of metallic nanowires as a result of their self-assembly while growing during the pulsed current electroplating process. Depending on the shape of the membrane and the regime of the pulsed current electroplating either one type of shell-like structures or various structures can be grown.Comment: 11pages, 10 figure

Current-induced magnetization dynamics at the edge of a two-dimensional electron system with strong spin-orbit coupling

We experimentally investigate electron transport through the interface between a permalloy ferromagnet and the edge of a two-dimensional electron system with strong Rashba-type spin-orbit coupling. We observe strongly non-linear transport around zero bias at millikelvin temperatures. The observed nonlinearity is fully suppressed above some critical values of temperature, magnetic field, and current through the interface. We interpret this behavior as the result of spin accumulation at the interface and its current-induced absorption as a magnetization torque.Comment: 6 pages, minor correction

Interacting galaxy NGC4656 and its unusual dwarf companion

We studied the nearby edge-on galaxy NGC4656 and its dwarf low surface brightness companion with the enhanced UV brightness, NGC4656UV, belonging to the interacting system NGC4631/56. Regular photometric structure and relatively big size of NGC4656UV allows to consider this dwarf galaxy as a separate group member rather than a tidal dwarf. Spectral long-slit observations were used to obtain the kinematical parameters and gas-phase metallicity of NGC4656UV and NGC4656. Our rough estimate of the total dynamical mass of NGC4656UV allowed us to conclude that this galaxy is the dark-matter dominated LSB dwarf or ultra diffuse galaxy. Young stellar population of NGC4656UV, as well as strong local non-circular gas motions in NGC4656 and the low oxygen gas abundance in the region of this galaxy adjacent to its dwarf companion, give evidence in favour of the accretion of metal-poor gas onto the discs of both galaxies.Comment: 8 pages, 2 tables, 9 figures, accepted for publication in MNRA

Optical and infrared emission of H II complexes as a clue to the PAH life cycle

We present an analysis of optical spectroscopy and infrared aperture photometry of more than 100 H II complexes in nine galaxies. Spectra obtained with the 6-m telescope of SAO RAS are used along with archival data from Spitzer and several ground-based telescopes to infer a strength of polycyclic aromatic hydrocarbon (PAH) emission, age, properties of the UV radiation field, and metallicity of studied H II complexes. Physical properties (age, radiation field parameters, metallicity) are related to the $F_{8}/F_{24}$ ratio used as a proxy for the PAH abundance in order to reveal factors that may influence the PAH evolution in H II complexes. The well-known correlation between the $F_{8}/F_{24}$ ratio and metallicity is confirmed in the studied complexes. The infrared flux ratio also correlates with the [O III]$\lambda 5007/\mathrm{H\beta}$ ratio which is often considered as an indicator of the radiation field hardness, but this correlation seems to be a mere reflection of a correlation between [O III]$\lambda 5007/\mathrm{H\beta}$ and metallicity. In separate metallicity bins, the $F_{8}/F_{24}$ ratio is found to correlate with an age of an H II complex, which is estimated from the equivalent width of $\mathrm{H}\beta$ line. The correlation is positive for low metallicity complexes and negative for high metallicity complexes. Analysing various mechanisms of PAH formation and destruction in the context of found correlations, we suggest that PAH abundance is likely altered by the UV radiation within H II complexes, but this is not necessarily due to their destruction. If PAHs can also form in H II complexes due to some processes like aromatisation, photodestruction, shattering and sputtering of very small grains, the net $F_{8}/F_{24}$ ratio is determined by a balance between all these processes that can be different at different metallicities.Comment: Accepted to MNRA

Dust Evolution in the Dwarf Galaxy Holmberg II

A detailed photometric study of star-forming regions (SFRs) in the galaxy Holmberg II has been carried out using archival observational data from the far infrared to ultraviolet obtained with the GALEX, Spitzer, and Herschel telescopes. Spectroscopic observations with the 6-m telescope of Special Astrophysical Observatory of the Russian Academy of Sciences are used to estimate ages and metallicities of SFRs. For the first time, the ages of SFRs have been related to their emission parameters in a wide spectral range and with the physical parameters determined by fitting the observed spectra. It is shown that fluxes at 8 and 24 micron characterizing the emission of polycyclic aromatic hydrocarbons (PAHs) and hot dust grains decrease with age, but their ratio increases. This implies that the relative PAH contribution to the total infrared flux increases with age. It is suggested that the detected increase in the ratio of the fluxes at 8 and 24 micron is related to the growth in the PAH mass due to destruction of larger grains.Comment: 15 pages, 8 figures, 3 tables. Published in Astronomy Letter