Application studies of the halotolerant protease from a newly isolated Virgibacillus dokdonensis VIT P14

Protease extracted from halotolerant bacterium - was tested for possible industrial applications. This enzyme was able to dissolve blood clot and coagulated egg within 30 min. The enzyme exhibited substantial keratinolytic activity. It was compatible with all the tested commercial detergents like Rin, Surfexcel, Henko, Tide, Ariel and Technobright and was found to be effective in the removal of blood strains from cotton fabric in the presence of these detergents. The enzyme was compatible with the organic solvents like xylene, toluene, hexane and ethanol and the maximum activity was observed in the presence of ethanol. The enzyme was tested for antimicrobial activity against gram positive and gram negative bacteria and it was found that it possesses good inhibition capability against Escherichia coli, Streptococcus eqiuns, Staphylococcus aureus and Salmonella enterica. The present report indicates that this halotolerant  protease has a wide range of properties and the conditions could be optimized to suit any particular industrial application

Magnetic skyrmions and skyrmion clusters in the helical phase of Cu2_2OSeO3_3

Skyrmions are nanometric spin whirls that can be stabilized in magnets lacking inversion symmetry. The properties of isolated skyrmions embedded in a ferromagnetic background have been intensively studied. We show that single skyrmions and clusters of skyrmions can also form in the helical phase and investigate theoretically their energetics and dynamics. The helical background provides natural one-dimensional channels along which a skyrmion can move rapidly. In contrast to skyrmions in ferromagnets, the skymion-skyrmion interaction has a strong attractive component and thus skyrmions tend to form clusters with characteristic shapes. These clusters are directly observed in transmission electron microscopy measurements in thin films of Cu$_2$OSeO$_3$. Topological quantization, high mobility and the confinement of skyrmions in channels provided by the helical background may be useful for future spintronics devices.Comment: 5 pages, 3 figures, 4 pages supplemen

High-energy high-momentum surface spin waves of ultrathin epitaxial 3d transition metal films

Surface spin waves on 3d ferromagnetic films are studied in the large wave vector regime with the help of a recently developed high resolution electron energy loss spectrometer. As a first study, face centered cubic (fcc) cobalt films were prepared by the epitaxial growth of cobalt on Cu(100). Spin waves were probed along the [110]- and the [010]-direction with in-plane wave vectors ranging from 0.02nm$^{-1}$ to 0.1nm$^{-1}$. The directional anisotropy in the surface spin wave dispersion is found to be very small in this system. In the low wave vector regime (wave vector < 0.035nm$^{-1}$), standing spin wave modes are observed in addition to the surface spin waves. In cobalt, like in other transition metal ferromagnets, the 3d electrons are not localized. Rather they form a band of considerable width which offers the possibilityfor spin-flip excitations (Stoner-excitations) in a wide energy-momentum range. The damping of spin waves by Stoner excitations results in large energy width of the spin wave signals. For the well-defined spin waves of cobalt, the line-widths of the surface spin wave signals were quantitatively determined. As a next step, epitaxial nickel films were prepared by deposition on Cu(100). In agreement with earlier unpublished work, no spin wave excitation is observed in Ni by inelastic electron scattering presumably due to the strong damping of the spin waves. As an attempt to study the effect of nickel on cobalt surface spin waves, layers of Ni were deposited on top of Co/Cu(100). Spin waves are seen for up to three monolayers of Ni. By a careful study of the intensity of spin waves as a function of Ni layer thickness, it is proven that spin waves are localized at the Co side of the Ni/Co interface. The presence of Ni broadens the spin wave peak compared to bare Co spin waves, indicating additional decay channels provided by the nickel capping layer. The 3d-band of copper is fully occupied, and hence copper has less low energy excitations. As a consequence, the mean free path of electrons in copper is much larger than in nickel. This provided the opportunity to look at spin waves localized at the Co interface through thicker layers (up to $\approx$ 12 layers) of copper. A similar spin wave broadening as for nickel is observed for copper. One of the extensively studied systems in thin film magnetism is Fe/Cu(100) due to its richness in structural and magnetic phenomena. At least three different magnetic phases can be stabilized depending on the film thickness. In this thesis, surface spin waves of three to five monolayer iron films were studied. From the similarity to the surface spin wave dispersion of bcc Fe films, it is concluded that the observedspin waves arise from the so-called $\textit{nanomartensitic}$ phase. The nanomartensitic phase is locally similar to a bcc structure, however lacking the perfect long range order of the latter. The spin wave dispersion measured on iron films deposited on fcc Co(100) is found to be nearly identical to that of Fe/Cu(100), indicating the structural similarity of the two systems

Standing spin waves in ultrathin magnetic films: A method to test for layer-dependent exchange coupling

We introduce a method to test theoretical models for the layer dependence of exchange coupling constants in ultrathin magnetic films. The method is based on the observation of high-energy and high-momentum standing spin wave modes using high-resolution electron energy loss spectroscopy. Experimental data are presented for 5–8 layers of fcc cobalt deposited on Cu(100). The power of the method is illustrated by comparison to two theoretical studies predicting rather different results concerning the ratio of the interlayer and intralayer exchange coupling constants near the surface. Only the theory with a large interlayer coupling shows sufficient energy spreading in the layer dependence of the dispersion curves to match the experimental data. We furthermore discuss the reason for the surprising success of the simple nearest-neighbor Heisenberg model with a single exchange constant matched to experiment

Large wave vector surface spin waves of the nanomartensitic phase in ultrathin iron films on Cu(100)

It is generally accepted that thin-film magnetism is strongly affected by even small structural modifications. Much less is known about the influence of structure on magnetic excitations, in particular, spin waves. Using electron energy loss spectroscopy we have studied the dispersion of large wave vector surface spin waves of a system for which details of the structure became known only recently, namely ultrathin iron films grown on Cu(100) surfaces. We find the spin wave dispersion to be nearly identical to the dispersion reported for bcc Fe(110) layers grown on W(110). We therefore conclude that the observed spin wave signal stems from the “nanomartensitic” phase of Fe/Cu(100) and that this phase is not merely a surface phase but encompasses the deeper layers

In Situ Electric Field Skyrmion Creation in Magnetoelectric Cu2OSeO3

Exploiting additional degrees of freedom in solid-state materials may be the most-promising solution when approaching the quantum limit of Moore's law for the conventional electronic industry. Recently discovered topologically nontrivial spin textures, skyrmions, are outstanding among such possibilities. However, the controlled creation of skyrmions, especially by electric means, remains a pivotal challenge in technological applications. Here, we report that skyrmions can be created locally via electric field in the magnetoelectric helimagnet Cu2OSeO3. Using Lorentz transmission electron microscopy, we successfully write skyrmions in situ from a helical-spin background. Our discovery is highly coveted because it implies that skyrmionics can be integrated into modern field effect transistor based electronic technology, in which very low energy dissipation can be achieved and, hence, realize a large step forward toward its practical applications

Design and implementation of an optimal laser pulse front tilting scheme for ultrafast electron diffraction in reflection geometry with high temporal resolution

Ultrafast electron diffraction is a powerful technique to investigate out-of-equilibrium atomic dynamics in solids with high temporal resolution. When diffraction is performed in reflection geometry, the main limitation is the mismatch in group velocity between the overlapping pump light and the electron probe pulses, which affects the overall temporal resolution of the experiment. A solution already available in the literature involved pulse front tilt of the pump beam at the sample, providing a sub-picosecond time resolution. However, in the reported optical scheme, the tilted pulse is characterized by a temporal chirp of about 1 ps at 1 mm away from the centre of the beam, which limits the investigation of surface dynamics in large crystals. In this paper, we propose an optimal tilting scheme designed for a radio-frequency-compressed ultrafast electron diffraction setup working in reflection geometry with 30 keV electron pulses containing up to 105 electrons/pulse. To characterize our scheme, we performed optical cross-correlation measurements, obtaining an average temporal width of the tilted pulse lower than 250 fs. The calibration of the electron-laser temporal overlap was obtained by monitoring the spatial profile of the electron beam when interacting with the plasma optically induced at the apex of a copper needle (plasma lensing effect). Finally, we report the first time-resolved results obtained on graphite, where the electron-phonon coupling dynamics is observed, showing an overall temporal resolution in the sub-500 fs regime. The successful implementation of this configuration opens the way to directly probe structural dynamics of low-dimensional systems in the sub-picosecond regime, with pulsed electrons

In Situ Electric Field Skyrmion Creation in Magnetoelectric Cu₂OSeO₃

Exploiting additional degrees of freedom in solid-state materials may be the most-promising solution when approaching the quantum limit of Moore’s law for the conventional electronic industry. Recently discovered topologically nontrivial spin textures, skyrmions, are outstanding among such possibilities. However, the controlled creation of skyrmions, especially by electric means, remains a pivotal challenge in technological applications. Here, we report that skyrmions can be created locally via electric field in the magnetoelectric helimagnet Cu₂OSeO₃. Using Lorentz transmission electron microscopy, we successfully write skyrmions in situ from a helical-spin background. Our discovery is highly coveted because it implies that skyrmionics can be integrated into modern field effect transistor based electronic technology, in which very low energy dissipation can be achieved and, hence, realize a large step forward toward its practical applications