The development of spintronic emitters of broadband THz pulses relies on designing heterostructures where processes of laser-driven spin current generation and subsequent spin-to-charge current conversion are the most efficient. An interface between ferromagnetic and nonmagnetic layers in the emitter is one of the critical elements. Here, we study experimentally single-cycle THz pulse generation from a laser-pulse excited Pt/Co emitter with a composition gradient interface between Pt and Co and compare it with the emission from a conventional Pt/Co structure with an abrupt interface. We find that the gradient interface enhances the efficiency of optics-to-THz conversion by a factor of two in a wide range of optical fluences up to 3 mJ cm^-2. We reveal that this enhancement is caused by a pronounced increase in transmittance of the laser-driven spin-polarized current through the gradient interface compared to the abrupt one. Furthermore, we find that such a transmission deteriorates with laser fluence due to the spin accumulation effect.

Analysis of fluctuations of satellite radio signals scattered on small-scale inhomogeneities in the F-region of the ionosphere and received by a ground receiver in Moscow shows that both a single maximum and two or three maxima can be observed in the latitudinal profile of the variance of the logarithm of the relative amplitude. The orientation of the transverse anisotropy of the inhomogeneities is determined and compared to the direction of the drift, obtained by the DPS-4 ionosonde using the LocalDrift software.

The article focuses on the micromagnetic modeling of the nucleation, energetic stability regions, and dynamic of chiral spin textures in thin-film heavy-metal/ferromagnetic (FM) systems with Dzyaloshinskii–Moriya interaction. A simple two-layer model for analyzing ferrimagnetic (FIM) structures is proposed. The analytical description and simulation of the mechanisms of stabilization and current-induced motion of skyrmions in both FM and FIM films are carried out, depending on the parameters of the magnetic model and the external magnetic field. The influence of the magnetization, magnetic anisotropy, and damping on the parameters and velocity of skyrmions (e.g. size, stability regions etc.) in thin-film structures is estimated. The specific dynamics of skyrmion motion under the influence of spin-polarized current as a function of the magnitude and sign of the Dzyaloshinskii–Moriya interaction is also identified. The results demonstrate the promising potential of FIM films for skyrmions stabilization and investigation of its dynamics.

Magneto-optical gyrotropic Faraday and Kerr effects are studied in the BiY2Fe5O12 films with thicknesses ranging from 16 to 55 nm, in the wavelength range of 295 nm < lambda < 830 nm (4.2-1.5 eV), and under magnetic fields of up to 1.2 T. It is shown that films produced by ac magnetron sputtering on the single-crystalline diamagnetic yttrium aluminum garnet substrates Y3Al5O12 (001) exhibit high structural and magneto-optical quality. The Verdet constant for diamagnetic Y3Al5O12 is determined, and the magnitude of the Kerr effect is estimated for the polished substrate. It is shown experimentally that for a substrate with diffusely reflective backside, the Kerr effect is about zero, except in the high-energy region. For all BiY2Fe5O12 films investigated, in the saturating magnetic fields of approximately 0.16-0.2 T, the value of specific Faraday rotation reaches 20 deg/mu m (200 000 deg/cm), while the value of the Kerr effect reaches approximately 20 min (5.8 mrad). The critical thickness of the film-substrate interface was estimated, highlighting variations in the Kerr effect spectra associated with a decrease in the Bi content in thin films with the thicknesses of below 27 nm.

Here we report recent data on the phenomenon of total nonreflection of spin waves (NRSWs). Using space- and phase-resolved Brillouin light scattering we experimentally studied the amplitude, direction, and phase of the NRSW in yttrium iron garnet films with artificial defects---an antidot array. An NRSW in the form of a focused beam of high intensity with the group velocity pointing along the line of defects is observed only for a critical angle between spin-wave phase velocity and an antidot array direction in a magnetic field. It is shown that the NRSW is an independent noncollinear spin wave arising as a result of the anisotropic nature of the propagation of surface magnetostatic spin waves in a magnetic medium. The numerical simulations agree well with experimental data. Micromagnetic simulations performed let us elucidate the phenomenon of the NRSW and map the spin-wave profile of dynamic magnetization inside the NRSW. The estimated mean free path of the NRSW reaches about 1 mm in the yttrium iron garnet film with a thickness of a few micrometers. These results demonstrate a unique approach to focusing and enhancing spin waves in magnetics through the use of artificial defects.

Magnetic circular dichroism (MCD) spectroscopy for manganite films of various compositions and morphologies has been studied in the range of 1.2-3.7 eV. The primary focus was on the temperature behavior of the MCD spectra, as well as the magnetization and resistivity of the films. The data obtained were analyzed in comparison with magneto-optical spectroscopy of the Kerr rotation (KR) on both single crystal and thin film of manganites. It has been established that the MCD response at 2.3 eV is typical for manganites transitioning into a conducting state. Consequently, it reflects a change in the band structure of the material. This response is also observed in the KR spectrum of manganites in the range 2.3-2.6 eV below the metal-insulator transition temperature. These findings complement the understanding of the electronic structure of manganites in general. Moreover, they also provide a basis for the search for new functional materials.

Micromagnetic modeling of non-linear autoresonance magnetization oscillations in thin films of yttrium iron garnet (YIG) with specified growth directions is conducted. It is found that in the case of rapid frequency modulation (sweep rate of the order of 1016 Hz/sec) of 1Oe excitation magnetic field, the maximum precession angle of magnetization can achieve up to 160 degrees. For the first time, the influence of demagnetization fields, magneto-crystalline anisotropy, and Gilbert damping on autoresonance phenomena in YIG films is numerically calculated. It is shown that demagnetization fields and damping have a weak influence on parameters of autoresonance. Simultaneously, damping provides a shorter phase-locking time between the excitation field and intrinsic magnetization oscillations in the film, favoring high amplitude of magnetization oscillations. The magneto-crystalline anisotropy leads to a reduction of the threshold sweep rate of the pumping field for YIG films with [100] direction, as well as the emergence of parametric instability for [210] films. The results of the work are aimed to be applied for the experimental observation of autoresonance phenomena in thin yttrium iron garnet films.

Multilayered metallic nanostructures are promising for the fabrication of spin valves based on the giant magnetoresistive effect and for studies of the nature of topological magnetism, aimed at the development of new nanoscale data storage and transfer devices, e.g. those based on magnetic skyrmions. It is still an important task to develop methods of synthesis and configuration of thin-film nanostructures and control of spin textures in those nanostructures under electric and spin currents generated as a result of the spin Hall effect in external electric fields. Thin-film polycrystalline ferromagnetic / heavy metal Ru(10nm)/Co(0,8)/Ru(2), Ru(10)/Co(0,8)/Ru(2)/W(4), Pt(5)/Co(0,8)/MgO(2)/Pt(2) and Pt(15)/Co(0,8)/MgO(2)/Pt(2) nanostructures have been synthesized using magnetron sputtering. Electric contacts and Hall structures with different conductive bridge thicknesses have been synthesized on the specimens using electron beam photolithography. Experimental vibration magnetometric data have been utilized to calculate magnetic parameters of the specimens, i.e., saturation magnetization, magnetic anisotropy energy and field and coercive force as functions of ferromagnetic and heavy metal layer types. The domain structure of the specimens has been studied using Kerr microscopy. The electrical resistivity has been simulated and the critical current and current density of the nanostructures have been assessed. We show that all the film specimens exhibit perpendicular magnetic anisotropy and can be used in the studies of current-induced phenomena and spin moment transfer processes in nanostructures.

Annotation: Magnetooptical Faraday and Kerr effects are studied in the nanosized BiY2Fe5O12 films within the spectral region of 1.3 eV<E<4.5 eV and magnetic fields of up to 10 kOe. It is shown that the thin-films BiY2Fe5O12 with the thicknesses ranging from 5 to 51 nm obtained by magnetron sputtering on the single-crystalline Gd3Ga5O12 substrates have high magneto-optical quality. The specific Faraday rotation for the nanosized Bi0.5Y1.5Fe5O12-delta films reaches about 140000 deg/cm close to that for bulk BiY2Fe5O12. Meanwhile, the polar Kerr effect reaches about 30 min within the range of 1.6 eV-4.1 eV at the magnetic fields above 2 kOe. It is shown that the strong paramagnetic contribution of Gd3Ga5O12 substrates significantly affects the Faraday and Kerr effect for the films. The defining of magnetooptical parameters and Verdet constant for the Gd3Ga5O12 substrate permitted to separate the substrate contribution and reveal peculiarities of spectral dependences of both Faraday and Kerr effects for magnetic films of various thicknesses. The estimated critical thickness of the film-substrate interface region is as large as 35 lattice constants of BiY2Fe5O12. It is shown that the magnetooptical effects for the thin films with the thickness above the critical one correspond to those for bulk BiY2Fe5O12. For samples with the smallest thicknesses of the film (5 nm) the contributions from magnetically dead and magnetically passive layers lead to a drastic reduction in the observable Faraday and Kerr effects with a dominating contribution from the substrate. The high density of displacement dislocations at the film-substrate interface leads to the decrease the magnetooptical quality of the nanosized films.

Thin (~50 nm thick) BaM hexaferrite (BaFe12O19) films were grown on (1–102) and (0001) cut α-Al2O3 (sapphire) substrates via laser molecular beam epitaxy using a one- or two-stage growth protocol. The advantages of a two-stage protocol are shown. The surface morphology, structural and magnetic properties of films were studied using atomic force microscopy, reflected high-energy electron diffraction, three-dimensional X-ray diffraction reciprocal space mapping, powder X-ray diffraction, magneto-optical, and magnetometric methods. Annealed BaFe12O19/Al2O3 (1–102) structures consist of close-packed islands epitaxially bonded to the substrate. The hexagonal crystallographic axis and the easy axis (EA) of the magnetization of the films are deflected from the normal to the film by an angle of φ~60°. The films exhibit magnetic hysteresis loops for both in-plane Hin-plane and out-of-plane Hout-of-plane magnetic fields. The shape of Mout-of-plane(Hin-plane) and Min-plane(Hin-plane) hysteresis loops strongly depends on the azimuth θ of the Hin plane, confirming the tilted orientation of the EA. The Mout-of-plane(Hout-of-plane) magnetization curves are caused by the reversible rotation of magnetization and irreversible magnetization jumps associated with the appearance and motion of domain walls. In the absence of a magnetic field, the magnetization is oriented at an angle close to φ.

A model for micromagnetic simulation of the magnetization of a ferrimagnetic film consisting of an alloy of ferromagnetic and rare-earth metals is proposed and discussed. It is shown that the model qualitatively replicates the experimentally observed temperature dependencies of the saturation magnetization of various ferrimagnetic alloys for different percentages of the rare-earth element and that it exhibits a similar magnetic hysteresis loop. The results of the study are of interest for the theoretical analysis of the magnetization behavior of ferromagnetic–heavy-metal film nanostructures, as well as for solving problems of applied materials science and magnetism.

Thin films of BaM hexaferrite (BaFe12O19) were grown on α-Al2O3(0001) substrates by laser molecular beam epitaxy. Structural, magnetic, and magneto-optical properties were studied using medium-energy ion scattering, energy dispersive X-ray spectroscopy, atomic force microscopy, X-ray diffraction, magneto-optical spectroscopy, and magnetometric techniques, and the dynamics of magnetization by ferromagnetic resonance method. It was shown that even a short time annealing drastically changes the structural and magnetic properties of films. Only annealed films demonstrate magnetic hysteresis loops in PMOKE and VSM experiments. The shape of hysteresis loops depends on thickness of films showing practically rectangular loops and high value of remnant magnetization (Mr/Ms~99%) for thin films (50 nm) and much broader and sloped loops in thick (350–500 nm) films. The magnitude of magnetization 4πMs ≈ 4.3 kG in thin films corresponds to that in bulk BaM hexaferrite. Photon energy and sign of bands in magneto-optical spectra of thin films correspond to ones observed earlier in bulk samples and films of BaM hexaferrite. FMR spectra of 50 nm films at 50 GHz consist of a number of narrow lines. The width of main line ΔH~20 Oe is lower than has been reported up to now.

The single crystal of ferromagnetic magnetostrictive spinel MnFe2O4 was grown by the zone-floating method. The magnetic, magneto-elastic, optical, and magneto-optical properties of the MnFe2O4 ferrite-spinel were investigated in the infrared spectral range. A strain-magneto-optical phenomenon, which demonstrate the connection between magnetoreflection of non-polarized light and magnetostriction of MnFe2O4, was revealed. A maximum magnetoreflection of up to 1 % was observed at room temperature in a magnetic field of 2 kOe. Using the Kramers-Kronig method, the magnetorefractive effect and magnetooptical conductivity of MnFe2O4 were also calculated. The observed correlation between magnetoelastic and magneto-optical properties of MnFe2O4 was attributed to the significant contribution of linear magnetostriction to the magnetic anisotropy constant (Delta K/K1 -8 %) in the MnFe2O4 crystal. Additionally, a criterion of Delta K/K1 -1 % was proposed to evaluate the potential use of magnetostrictive materials in strain-magneto-optics.

Magnetic circular dichroism (MCD) spectroscopy was used to study the features of the electronic structure of an epitaxial La0.7Ca0.3MnO3 film in the range of 1.2 - 4 eV. The study of the temperature behavior of the MCD spectra made it possible to establish a correlation between the magnetooptical and transport properties of the sample. The data obtained were analyzed in comparison with MCD data for polycrystalline manganite films of various RE1-xAxMnO3 compositions. The MCD spectra of the films were compared with the spectra of the off-diagonal component of the permittivity tensor calculated from the data of the magneto-optical Kerr effect for films of the same composition. A unified set of ground and excited electronic states characteristic of RE1-xAxMnO3 manganites in the visible and near infrared ranges has been identified. These results are important for a qualitative theoretical description of the electronic structure of strongly correlated magnetic oxides.

We study the electronic structure of the ferromagnetic spinel HgCr_{2}Se_{4} by soft-x-ray angle-resolved photoemission spectroscopy (SX-ARPES) and first-principles calculations. While a theoretical study has predicted that this material is a magnetic Weyl semimetal, SX-ARPES measurements give direct evidence for a semiconducting state in the ferromagnetic phase. Band calculations based on the density functional theory with hybrid functionals reproduce the experimentally determined band gap value, and the calculated band dispersion matches well with ARPES experiments. We conclude that the theoretical prediction of a Weyl semimetal state in HgCr_{2}Se_{4} underestimates the band gap, and this material is a ferromagnetic semiconductor.

Nonreciprocity, i.e. inequivalence in amplitudes and frequencies of spin waves propagating in opposite directions, is a key property underlying functionality in prospective magnonic devices. Here we demonstrate experimentally and theoretically a simple approach to induce frequency nonreciprocity in a magnetostatically coupled ferromagnetic bilayer structure with a nonmagnetic spacer by its geometrical asymmetry. Using Brillouin light scattering, we show the formation of two collective spin wave modes in Fe81Ga19/Cu/Fe81Ga19 structure with different thicknesses of ferromagnetic layers. Experimental reconstruction and theoretical modeling of the dispersions of acoustic and optical collective spin wave modes reveal that both possess nonreciprocity reaching several percent at the wavenumber of 22 × 104 rad cm-1. The analysis demonstrates that the shift of the amplitudes of counter-propagating coupled modes towards either of the layers is responsible for the nonreciprocity because of the pronounced dependence of spin wave frequency on the layers' thickness. The proposed approach enables the design of multilayered ferromagnetic structures with a given spin wave dispersion for magnonic logic gates.

Optical and magneto-optical properties of the La0.65Ba0.35MnO3 /SrTiO3(0 0 1) thin film with CMR and the paramagnetic-to-ferromagnetic transition at T = 310 K have been investigated in the infrared spectral range. It is shown that magnetotransmission and magnetoreflection of unpolarized light in the film reach up to 10 % at the magnetic field of 4 kOe. The possible physical mechanisms responsible for negative magnetotransmission and positive magnetoreflection in the mid-infrared range are interpreted in the framework of the theory of magne-torefractive effect in manganites. High optical response of the La0.65Ba0.35MnO3 film to an external magnetic field (up to -25 %/kOe in the magnetoreflection) could be used in the design of optical magnetic field sensor, switches and modulators.

Autoresonance is a new non-linear method for excitation of spin subsystem in magnetics by an extremely low magnetic field. Here, we consider the autoresonance (autophasing) process in a model of yttrium iron garnet (YIG) film possessing out-of-plane uniaxial anisotropy. As a result of simulation in MuMax3 software, the parameters of exciting field are determined and a model is proposed for successful auto-phase locking at GHz frequencies. The numerical data obtained for the model with material parameters close to ones for low-damping yttrium iron garnet films are in good agreement with theoretical predictions. It is shown that the process of phase locking leads to a soliton-like character of the excited magnetic oscillations with a high-amplitude of precession. The maximum angle of magnetization deflection reaches up to 150° at the exciting field of 1 mT sweeping with the rate 4.3 × 1016 s−2. It is presented the stability of the autoresonance in the case of low damping in the developed model. Besides, the damping could be used for adjusting the parameters of the autoresonance, which paves the way for potential experimental testing.

From the various aspects of spintronics the review highlights the area devoted to the creation of new functional materials based on magnetic semiconductors and demonstrates both the main physical phenomena involved and the technical possibilities of creating various devices: maser, p-n diode with colossal magnetoresistance, spin valve, magnetic lens, optical modulators, spin wave amplifier, etc. Particular attention is paid to promising research directions such as ultrafast spin transport and THz spectroscopy of magnetic semiconductors. Special care has been taken to include a brief theoretical background and experimental results for the new spintronics approach employing magnetostrictive semiconductors—strain-magnetooptics. Finally, it presents top-down approaches for magnetic semiconductors. The mechano-physical methods of obtaining and features of the physical properties of high-density nanoceramics based on complex magnetic oxides are considered. The potential possibility of using these nanoceramics as an absorber of solar energy, as well as in modulators of electromagnetic radiation, is shown.

We collate the drift directions of medium-scale irregularities (MSI) and the orientation of the cross-field anisotropy of small-scale irregularities (SSI) in the F region of the mid-latitude ionosphere. Experimental data were obtained in May–December 2009 in quiet geomagnetic conditions by two independent methods, namely, ionospheric transmission radio sounding from spacecraft (ground-based receiver at the Lomonosov Moscow State University) and radar (DPS-4 ionosonde at IZMIRAN). Using the new LocalDrift program, which permits calculating the direction and velocity of drift in any selected area of the sky map, the drift characteristics are determined in exactly those spatially bounded areas where small-scale irregularities have been studied by transmission radio sounding. It is shown that small-scale field-aligned irregularities are transversely anisotropic. In most cases, they are elongated in a plane perpendicular to the geomagnetic field along the drift direction of medium-scale irregularities. These statements are valid if the experimental data are obtained simultaneously and in the same local region of the ionosphere.