Sergey Samarin

Highly efficient time-of-flight spectrometer for studying low-energy secondary emission from dielectrics: Secondary-electron emission from LiF film

A highly efficient time-of-flight electron spectrometer is described. An incident electron current of the order of 10−14 A makes it suitable for studying secondary emission from dielectric surfaces. A microchannel plate position-sensitive detector allows flight distance correction while keeping a large acceptance angle. Measured energy distribution curves of secondary electrons generated from a LiF film by 19–31 eV incident electrons demonstrate good energy resolution and reveal reproducible and stable emission features at 2.6±0.3 eV, 7.2±0.3 eV, and 10.3±0.3 eV.

Plasmon-assisted high reflectivity and strong magneto-optical Kerr effect in permalloy gratings

We demonstrate experimentally a strong plasmon-assisted enhancement of the transverse magneto-optical Kerr effect in permalloy gratings. The enhanced transverse magneto-optical Kerr effect is accompanied by an increased grating reflectivity with the maximum of enhancement being correlated with plasmonic Fano resonances. This correlation was confirmed by an intuitive Fano model and also through full-vectorial optical simulations. Simultaneously high reflectivity and transverse magneto-optical Kerr effect as well as narrowest ferromagnetic resonance linewidth and vanishing anisotropy make permalloy nanostructures attractive for applications in spintronics and nano-optics such as, for example, all-optical excitation of propagating spin waves and spectral tuning of optical nanoantennas.

Spin-dependent interactions: A fundamental basis for magnetism and spin-electrons

The spin-dependent interactions in mesons are considered in detail in the framework of the Field Correlator Method. Analytic expressions for the spin-dependent potentials in heavy and light quarkonia are derived with the QCD string moment of inertia taken into account. Recent lattice data are analysed using these formulae and the data are shown to be consistent with very small values of the gluonic correlation length, . 0.1 fm. The Field Correlator and the Eichten–Feinberg definitions of the spin-dependent potentials in the lowest, Gaussian approximation for the QCD vacuum are compared to one another and the two approaches are shown to be equivalent in the limit of a vanishing vacuum correlation length, whereas for finite values of the latter the difference between these two approaches can be explained by the contribution of the higher-order field corelators, starting from the quartic one.

Collective spin waves on a nanowire array with step-modulated thickness

It is shown experimentally that collective Bloch spin waves are able to propagate in a dense periodic array of nanowires with step-modulated thickness along the periodicity direction. The spin wave dispersion (frequency versus wave vector k) was measured using the Brillouin light scattering technique by sweeping the wave vector perpendicularly to the wire length. Remarkably, the mode measured at the lowest frequency exhibits an oscillating dispersion and its frequency is up-shifted with respect to the homogeneous-thickness wires of the same width. The modes located at higher frequencies have negligible dependencies on the wave number, i.e. are practically dispersionless. Complementary ferromagnetic resonance measurements enabled us to independently measure the whole set of modes at k = 0, showing a good agreement with the Brillouin light scattering data. These results have been successfully reproduced in a numerical simulation employing a two-dimensional Green’s function description of the dynamic dipole field of the precessing magnetization. The theory also allowed visualizing the non-trivial distribution of dynamic magnetization across the wire cross-section and estimating the Brillouin light scattering cross-section. The analysis of these intensities suggests complicated magneto-optical coupling between the light and the dynamic magnetization in the arrays of nanowires with step-modulated thickness. This work can stimulate the design, tailoring, and characterization of three-dimensional magnonic crystals.

Microwave magnetic dynamics in highly conducting magnetic nanostructures

We performed low-noise broadband microstrip ferromagnetic resonance (FMR) measurements of the resonant modes of an array of metallic ferromagnetic nanostripes. In addition to a strong signal of the fundamental mode, we observed up to five weak-amplitude peaks in the field-resolved FMR traces, depending on the frequency. These higher-order absorption peaks have been theoretically identified as due to resonant excitation of odd and even standing spin waves across the direction of confinement in array plane (i.e., across the stripe width). The theory we developed suggests that the odd modes become excited in the spatially uniform microwave field of the FMR setup due to the large conductivity of metals. This promotes excitation of large-amplitude eddy currents in the sample by the incident microwave magnetic field and ultimately results in excitation of these modes. Following this theory, we found that the eddy current contribution is present only for patterned materials and when the microwave magnetic field is incident on one surface of sample surface, as it is in the case of a microstrip FMR.

Coplanar probe microwave current injection ferromagnetic resonance of magnetic nanostructures

The non-uniform standing spin-wave modes in thin magnetic films and nanostructures provide important information about their magnetic properties. Very often they are lacking in the recorded ferromagnetic resonance spectra for symmetry reasons. In this work we experimentally demonstrate that by direct injection of microwave currents into a magnetic nanostructure using a sub-millimetre sized microwave coaxial to coplanar adaptor one can efficiently excite non-uniform standing spin wave modes with odd symmetry. The proposed method is quick and allows easy spatial mapping of magnetic properties with the resolution down to 100 μm. We have validated this method using an example from a periodical array of nanostripes.

Diffraction of correlated electron pairs from crystal surfaces

The spectra of the internal energy distribution of correlated electron pairs, ejected from W(0 0 1), Fe(1 1 0) and Cu(0 0 1) following the impact of a low-energy electron, show characteristic structure that can be associated with the diAraction of two-electron quasi-particles from the periodic surface potential. In this combined theoretical and experimental work we show that the positions of these features in momentum space are determined by the amount of change of the center-of-mass wave vector of the pairs with respect to the surface reciprocal lattice vector. This corresponds to a two-particle Bragg diAraction. The relative intensities of the peaks and the shapes of the peaks depend mainly on the internal correlation of the electron pair, i.e. on the strength of the electronic interaction. ” 2000 Elsevier Science B.V. All rights reserved.

Microwave magnetic dynamics in ferromagnetic metallic nanostructures lacking inversion symmetry

In this work, we carried out systematic experimental and theoretical investigations of ferromagnetic resonance (FMR) responses of quasi-two-dimensional magnetic objects—macroscopically long stripes with nanoscale cross-section made of ferromagnetic metals. We were interested in the impact of the symmetries of this geometry on the FMR response. Three possible scenarios from which the inversion symmetry break originated were investigated, namely: (1) from the shape of the stripe cross-section, (2) from the double-layer structure of the stripes with exchange coupling between the layers, and (3) from the single-side incidence of the microwave magnetic field on the plane of the stripe array. The latter scenario is a characteristic of the stripline FMR configuration. It was found that the combined effect of the three symmetry breaks is much stronger than the impacts of each of these symmetry breaks separately.

Investigation of the behaviour of the Sherman function for elastic electron scattering from Kr and Xe

We have investigated in detail certain rich structures in the Sherman function S arising when spin-polarized electrons are elastically scattered from the heavy noble gases, krypton and xenon. These structures exhibit large magnitudes which span several degrees of the scattering angle and change significantly as the incident electron energy varies. We follow the evolution of these structures as a function of energy both theoretically and experimentally and compare with published data.

An application of the electron mirror in the time-of-flight spectrometer

Abstract We suggest applying of the spherical electron mirror in the time-of-flight electron spectrometer with a position sensitive detector in order to increase the effective acceptance solid angle of the spectrometer. The spherical electron mirror is placed near the specimen and it focuses electrons on a position sensitive detector as a converging electron flux. The electron mirror increases the acceptance angle of the spectrometer by a factor of 20. The electron mirror of the spectrometer consists of an inner spherical electrode of the radius R and an outer spherical electrode of the radius 1.1R. The central segment of the inner electrode inside the linear angle of 80° is made of a grid. The detector plate radius is about 0.23R. The acceptance solid angle of the spectrometer with this electron mirror is about 1.1sr, the range of the polar angle of emission is 20°–90° relative to the surface normal, and the range of the azimuth angle of emission at its maximum is ±36° relative to the basic plane of the spectrometer. The design of the spectrometer allows to recover the electron trajectory for each detected electron and to calculate the energy and the emission angle of the electron. The energy resolution of the spectrometer is about 0.2 eV/ns for the electron energy of 10 eV. The energy range is from Emin≅0.1eUr up to eUr, where Ur is the retarding potential of the electron mirror. The perturbing influence of the grid of the electron mirror limits mainly the angular resolution of the spectrometer and affects relatively slightly the energy resolution. The electron spectrometer with two detectors and two electron mirrors symmetric about the spectrometer axis allows to measure electron pairs in coincidence in a wide range of emission angles and energies with k-resolutions.