Analyzer-free, intensity-based, wide-field magneto-optical microscopy

In conventional Kerr and Faraday microscopy, the sample is illuminated with plane-polarized light, and a magnetic domain contrast is generated by an analyzer making use of the Kerr or Faraday rotation. Here, we demonstrate possibilities of analyzer-free magneto-optical microscopy based on magnetization-dependent intensity modulations of the light. (i) The transverse Kerr effect can be applied for in-plane magnetized material, as demonstrated for an FeSi sheet. (ii) Illuminating that sample with circularly polarized light leads to a domain contrast with a different symmetry from the conventional Kerr contrast. (iii) Circular polarization can also be used for perpendicularly magnetized material, as demonstrated for garnet and ultrathin CoFeB films. (iv) Plane-polarized light at a specific angle can be employed for both in-plane and perpendicular media. (v) Perpendicular light incidence leads to a domain contrast on in-plane materials that is quadratic in the magnetization and to a domain boundary contrast. (vi) Domain contrast can even be obtained without a polarizer. In cases (ii) and (iii), the contrast is generated by magnetic circular dichroism (i.e., differential absorption of left- and right-circularly polarized light induced by magnetization components along the direction of light propagation), while magnetic linear dichroism (differential absorption of linearly polarized light induced by magnetization components transverse to propagation) is responsible for the contrast in case (v). The domain-boundary contrast is due to the magneto-optical gradient effect. A domain-boundary contrast can also arise by interference of phase-shifted magneto-optical amplitudes. An explanation of these contrast phenomena is provided in terms of Maxwell-Fresnel theory. © 2021 Author(s)

Self-assembly of Co/Pt stripes with current-induced domain wall motion towards 3D racetrack devices

Modification of the magnetic properties under the induced strain and curvature is a promising avenue to build three-dimensional magnetic devices, based on the domain wall motion. So far, most of the studies with 3D magnetic structures were performed in the helixes and nanowires, mainly with stationary domain walls. In this study, we demonstrate the impact of 3D geometry, strain and curvature on the current-induced domain wall motion and spin-orbital torque efficiency in the heterostructure, realized via a self-assembly rolling technique on a polymeric platform. We introduce a complete 3D memory unit with write, read and store functionality, all based on the field-free domain wall motion. Additionally, we conducted a comparative analysis between 2D and 3D structures, particularly addressing the influence of heat during the electric current pulse sequences. Finally, we demonstrated a remarkable increase of 30% in spin-torque efficiency in 3D configuration

Computer control of the spectral composition of the powerful laser system irradiation with a wide range of laser transitions on metal vapors

The results of the experimental study cycle of the multiwave metal vapor laser system on the basis of the original configuration of the multimedia laser emitter. The spectral parameters of the setup have been controlled using a personal computer (PC). This allows carrying out their independent optimization according to excitation conditions, and, therefore, promptly allocating the output set of oscillating wavelengths and their relative distribution in power, which makes the system attractive for scientific and technological application

Multi-wavelength metal vapor laser systems for solving applied problems of atmospheric spectroscopy

Results of a cycle of experimental investigations of a multi-wavelength metal vapor laser system based on original configuration of a multi-medium metal vapor laser source are presented. Novelty of our approach consists in that two gas discharge active elements (on copper bromide and strontium vapors) are arranged in a common cavity, and each of them is pumped by an independent power supply unit, which allows them to be optimized independently for excitation conditions and thereby the output set of lasing wavelengths and their relative power distribution to be regulated. This makes the above described system promising for a number of scientific and technological applications. The total output power of 11 spectral components lying in the range 0.43–6.45 μm reached ~17 W. © (2015) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only

The efficiency of the pumping of the lasers based on self-terminating atomic transitions operating in the energy input cut-off mode

The analysis of the electro-physical processes in the discharge circuit of the lasers based on the self-terminating transitions of metal atoms (LSTM) and the electrodes placed in the cold buffer zones of the gas discharge tube (GDT) is occurred. That design of the GDT can provide the efficient lasing at the reduction of the current flowing through the switch to zero after the charging of the capacitive components of the circuit from the storage capacitor. Under the circumstances the pumping of the active medium is determined by the energy input from the peaking capacitor and, consequently, the efficiency of the pumping can be increased by an order of magnitude, if (using a managed switch) the energy input into the active medium from the storage capacitor is “cut-off” after charging the capacitive components of the circuit. It was shown that the efficiency values of ∼ 9-11 % and of ∼ 5-6 % for the copper and gold vapor, lasers could be achieved

Direct imaging of nanoscale field-driven domain wall oscillations in Landau structures

Linear oscillatory motion of domain walls (DWs) in the kHz and MHz regime is crucial when realizing precise magnetic field sensors such as giant magnetoimpedance devices. Numerous magnetically active defects lead to pinning of the DWs during their motion, affecting the overall behavior. Thus, the direct monitoring of the domain wall's oscillatory behavior is an important step to comprehend the underlying micromagnetic processes and to improve the magnetoresistive performance of these devices. Here, we report an imaging approach to investigate such DW dynamics with nanoscale spatial resolution employing conventional table-top microscopy techniques. Time-averaged magnetic force microscopy and Kerr imaging methods are applied to quantify the DW oscillations in Ni81Fe19 rectangular structures with Landau domain configuration and are complemented by numeric micromagnetic simulations. We study the oscillation amplitude as a function of external magnetic field strength, frequency, magnetic structure size, thickness and anisotropy and understand the excited DW behavior as a forced damped harmonic oscillator with restoring force being influenced by the geometry, thickness, and anisotropy of the Ni81Fe19 structure. This approach offers new possibilities for the analysis of DW motion at elevated frequencies and at a spatial resolution of well below 100 nm in various branches of nanomagnetism

Synthesis of silymarin−selenium nanoparticle conjugate and examination of its biological activity in vitro

Silymarin (Sil) was conjugated to selenium nanoparticles (SeNPs) to increase Sil bioavailability. The conjugates were monodisperse; the average diameter of the native SeNPs was ~ 20-50 ± 1.5 nm, whereas that of the conjugates was 30-50 ± 0.5 nm. The use of SeNPs to increase the bioavailability of Sil was examined with the MH-22a, EPNT-5, HeLa, Hep-2, and SPEV-2 cell lines. The EPNT-5 (glioblastoma) cells were the most sensitive to the conjugates compared to the conjugate-free control. The conjugates increased the activity of cellular dehydrogenases and promoted the penetration of Sil into the intracellular space. Possibly, SeNPs play the main part in Sil penetration of cells and Sil penetration is not associated with phagocytosis. Thus, SeNPs are promising for use as a Sil carrier and as protective antigens

Voltage‐Controlled Deblocking of Magnetization Reversal in Thin Films by Tunable Domain Wall Interactions and Pinning Sites

High energy efficiency of magnetic devices is crucial for applications such as data storage, computation, and actuation. Redox‐based (magneto‐ionic) voltage control of magnetism is a promising room‐temperature pathway to improve energy efficiency. However, for ferromagnetic metals, the magneto‐ionic effects studied so far require ultrathin films with tunable perpendicular magnetic anisotropy or nanoporous structures for appreciable effects. This paper reports a fully reversible, low voltage‐induced collapse of coercivity and remanence by redox reactions in iron oxide/iron films with uniaxial in‐plane anisotropy. In the initial iron oxide/iron films, Néel wall interactions stabilize a blocked state with high coercivity. During the voltage‐triggered reduction of the iron oxide layer, in situ Kerr microscopy reveals inverse changes of coercivity and anisotropy, and a coarsening of the magnetic microstructure. These results confirm a magneto‐ionic deblocking mechanism, which relies on changes of the Néel wall interactions, and of the microstructural domain‐wall‐pinning sites. With this approach, voltage‐controlled 180° magnetization switching with high energy‐efficiency is achieved. It opens up possibilities for developing magnetic devices programmable by ultralow power and for the reversible tuning of defect‐controlled materials in general

Strong and ductile high temperature soft magnets through Widmanstätten precipitates

Fast growth of sustainable energy production requires massive electrification of transport, industry and households, with electrical motors as key components. These need soft magnets with high saturation magnetization, mechanical strength, and thermal stability to operate efficiently and safely. Reconciling these properties in one material is challenging because thermally-stable microstructures for strength increase conflict with magnetic performance. Here, we present a material concept that combines thermal stability, soft magnetic response, and high mechanical strength. The strong and ductile soft ferromagnet is realized as a multicomponent alloy in which precipitates with a large aspect ratio form a Widmanstätten pattern. The material shows excellent magnetic and mechanical properties at high temperatures while the reference alloy with identical composition devoid of precipitates significantly loses its magnetization and strength at identical temperatures. The work provides a new avenue to develop soft magnets for high-temperature applications, enabling efficient use of sustainable electrical energy under harsh operating conditions

Metal vapor lasers with increased reliability

Results of investigation and development of an excitation pulse generator with magnetic pulse compression by saturation chokes for pumping of active media of CuBr, Sr, and Ca vapor lasers are presented. A high-power IGBT transistor is used as a commutator. The generator can operate at excitation pulse repetition frequencies up to 20 kHz. The total average power for all laser lines of the CuBr laser pumped by this generator is ~6.0 W; it is ~1.3–1.7 W for the Sr and Ca lasers