Europium chalcogenides EuX (X = O, S, Se, and Te) represent a unique class of intrinsic magnetic semiconductors in which light can be used to directly control magnetic order on ultrafast time scales. This review synthesizes a series of pioneering magneto-optical phenomena in these materials, driven by their electronic structure: a valence band of highly localized 4f7 spins and a conduction band of empty 5d states. Optical excitation across the bandgap dramatically enhances the exchange interaction between 5d electrons and the 4f spin lattice, triggering remarkable effects. We demonstrate how femtosecond laser pulses can initiate magnetization precession through the optical orientation effect, generate colossal magnetic polarons with moments exceeding 105 [Formula: see text], and enable coherent control over spin dynamics. These findings elucidate the fundamental principles behind ultrafast light–spin coupling, elevating europium chalcogenides to a model system for this class of phenomena. The uncovered mechanisms inform the search for material platforms where magnetism can be controlled at the high speed.

The ability of light to manipulate fundamental interactions in a medium is central to research in optomagnetism and applications in electronics. A prospective approach is to create composite quasiparticles, magnetic polarons, highly susceptible to external stimuli. To control magnetic and transport properties by weak magnetic and electric fields, it is important to find materials that support photoinduced magnetic polarons with colossal net magnetic moments. Here, we demonstrate that magnetic polarons with a record-high magnetic moment, reaching and exceeding a hundred thousand Bohr magnetons, can be optically generated in EuO, an archetypal ferromagnetic semiconductor. The phenomenon is established employing the photoinduced Faraday effect studied in EuO films by a two-color pump-probe technique. The giant magnetic polarons are generated just above the Curie temperature once EuO is exposed to photons of an energy exceeding the bandgap. Picosecond temporal dynamics of magnetic polarons follows relaxation processes in the spin-split 5d conduction band occupied by the photoexcited electron. The study is expected to provide a platform for implementation of an efficient optical control over the magnetic state in solids.

ABSTRACT We present a sample of 950 edge-on spiral galaxies found with the use of an artificial neural network in the Hubble Space Telescope COSMOS field. This is currently the largest sample of distant edge-on galaxies. For all galaxies we analysed the 2D brightness distributions in the F814W filter and measured the radial and vertical exponential scales (h and hz correspondingly) of the brightness distribution. By comparing the characteristics of distant galaxies with those of nearby objects, we conclude that thin stellar discs with h/hz ≥ 10 at z ≈ 0.5 should be rarer than today. Both exponential scales of the stellar disc show evidence of luminosity-dependent evolution: in faint galaxies the h and hz values do not change with z, in bright (and massive) spiral galaxies both scales, on average, grow towards our epoch.

We have applied the method of star counts with Wolf diagrams to determine the interstellar extinction in five Galactic cirri in Sloan Digital Sky Survey (SDSS) Stripe 82. For this purpose, we have used the photometry of stars in the GALEX NUV filter and the photometry of red dwarfs in five SDSS bands and four SkyMapper Southern Sky Survey DR2 bands. We have identified the cirri as sky regions with an enhanced infrared emission from the Schlegel+1998 map. The extinction in them has been calculated relative to the nearby comparison regions with a reduced emission. The results for different filters agree well, giving the range of distances and the extinction law for each cirrus. The distances in the range 140–415 pc found are consistent with the 3D reddening maps. In the range between the $$B$$ and $$V$$ filters the extinctions found are consistent with the estimates from Schlegel+1998 for the Cardelli+1989 extinction law with $$R_{\mathrm{V}}=3.1$$ . However, the extinctions found for all of the filters are best described not by the Cardelli+1989 extinction law with some $$R_{\mathrm{V}}$$ , but by the inverse proportionality of the extinction and wavelength with its own coefficient for each cirrus. In one of the cirri our results suggest a very slight decrease in extinction with wavelength, i.e., a large contribution of gray extinction. In the remaining cirri a manifestation of gray extinction is not ruled out either. This is consistent with the previous measurements of the extinction law far from the Galactic midplane.

We present a new version of our analytical model of the spatial interstellar extinction variations within the nearest kiloparsec from the Sun. This model treats the three-dimensional (3D) dust distribution as a superposition of three overlapping layers: (1) the layer along the Galactic midplane, (2) the layer in the Gould Belt, and (3) the layer passing through the Cepheus and Chamaeleon dust cloud complexes. In each layer the dust density decreases exponentially with increasing distance from the midplane of the layer. In addition, there are sinusoidal longitudinal extinction variations along the midplane of each layer. We have found the most probable values of 29 parameters of our model using four data sets: the 3D stellar reddening maps by Gontcharov and Mosenkov (2017), Lallement et al. (2019), and Green et al. (2019) and the extinctions inferred by Anders et al. (2022) for 993 291 giants from the Gaia Early Data Release 3. All of the data give similar estimates of the model parameters. The extinction for a star or a point in space is predicted by our model with an accuracy from $$\sigma(A_{\textrm{V}})=0.07$$ to 0.37 for high and low Galactic latitudes, respectively. The natural fluctuations of the dust medium dominate in these values. When ignoring the fluctuations of the medium, the average extinction for an extended object (a galaxy, a star cluster, a dust cloud) or a small region of space is predicted by our model with an accuracy from $$\sigma(A_{\textrm{V}})=0.04$$ to 0.15 for high and low Galactic latitudes, respectively. Green et al. (2019) and Anders et al. (2022) give in unison an estimate of $$A_{\textrm{V}}=0.12^{m}$$ for the extinction at high latitudes across the whole Galactic dust half-layer above or below the Sun with the natural fluctuations of the medium $$\sigma(A_{\textrm{V}})=0.06^{m}$$ . If such a high estimate is subsequently confirmed, then it will require to explain how a substantial amount of dust ended up far from the Galactic midplane. Our model is a step in this explanation.

Aims. The origin and maintenance of spiral structure in galaxies, the correlation between different types of spiral structure and several proposed mechanisms for their generation, and the evolution of spiral arms of galaxies with time are questions that are still controversial. In this note we study the spiral structure in a sample of distant galaxies in order to infer the evolution of spiral arm characteristics with redshift. Methods. We considered a sample of 171 face-on spiral galaxies in the Hubble Space Telescope COSMOS (The Cosmic Evolution Survey) field. The galaxies are distributed up to z ≈ 1 with a mean value of 0.44. For all galaxies, we determined the pitch angles of the spiral arms and analysed their dependence on redshift; a total of 359 arms were measured. Results. Analyses of our measurements combined with the literature data suggest a possible evolution of the pitch angles of spiral galaxies: by the modern epoch the spiral pattern, on average, becomes more tightly wound. This may be a consequence of the general evolution of the structure of galaxies as galaxies become more massive over time and their bulges grow. In addition, the distribution of the cotangent of pitch angle of galaxies indicates the possibility that the dominant mechanism of spiral pattern generation changes over time.

Light-induced magnetization response unfolding on a temporal scale down to femtoseconds presents a way to convey information via spin manipulation. The advancement of the field requires exploration of new materials implementing various mechanisms for ultrafast magnetization dynamics. Here, pump-probe measurements of EuO-based ferromagnets by a time-resolved two-colour stroboscopic technique are reported. Epitaxial films of the pristine semiconductor and metallic Gd-doped EuO demonstrate photo-induced magnetization precession. Comparative experimental studies of both systems are carried out varying temperature, magnetic field, and polarization light helicity of the pump beam, followed by numerical estimates. The study establishes optical spin orientation by the electronic transition 4f75d0 → 4f65d1 as a mechanism triggering collective magnetization precession in these materials. The results suggest applications of EuO-based systems in optoelectronics and spintronics.

We have investigated the pitch angle ( $$\psi$$ ) of the spiral arms of galaxies in the Hubble Space Telescope (HST) COSMOS field. The sample consists of 102 face-on galaxies with a two-armed pattern at a mean redshift $$\langle z\rangle\approx 0.5$$ . The typical values of $$\psi$$ in the arms of distant galaxies are shown to be close to those for nearby spiral galaxies. Within one galaxy the scatter of $$\psi$$ for different arms is, on average, half the mean pitch angle. In the $$z$$ range from 1 to 0 we have found a tendency for $$\psi$$ to decrease. Our analysis of the $$\psi$$ distributions in galaxies at different redshifts is consistent with the assumption that in most of the galaxies at $$z\leq 0.5$$ the spiral arms are tidal in origin or they arose from transient recurrent instabilities in their disks.

We measured the slope of width growth with radius for spiral arms in 184 galaxies from the HST COSMOS field. The galaxies are viewed in an orientation close to face-on, and observed out to redshift z ≈ 1. The spiral arms are measured using an approximation of slices perpendicular to the arm originally proposed in Savchenko et al. (2020). It is shown that the typical values of the a parameter, which defines the increase of the arm width with the galactocentric distance, are, on average, significantly smaller for distant galaxies from the COSMOS field than for local ones. The average value is ⟨a⟩ = 0.06. It is shown that for the most galaxies, the width still increases with distance, and the opposite trend is observed for 25% of the cases. In the range of redshifts from 1 to 0, we observe a slight tendency for the parameter a to decrease.

Layered nanofilms based on Fe, Co, and Cu were grown on Si(001)2x1-Cu wetting layers with thicknesses of 1 and 2 ML and studied using the AES, EELS, and LEED methods in an ultrahigh vacuum chamber. After unloading into air, the samples were studied by AFM and MOKE methods. It was found that an increase in the thickness and annealing of the Si(001)2x1-Cu wetting layer increase the agglomeration of nanofilms and, as a consequence, their magnetization and coercive force. Although, annealing the Cu wetting layer reduces the degree of squareness of the magnetic hysteresis loop.

The influence of light exposure on the magneto-optical Kerr effect in the ferromagnetic semiconductor europium sulfide EuS has been studied. It has been experimentally established that when a sample is exposed to the light with a photon energy greater than the band gap, photoinduced magnetization occurs, which is associated with the formation of magnetic polarons with a large magnetic moment of about 3000 μB. The polarons are excited in a narrow temperature range of 12–18 K and form a superparamagnetic ensemble with an average polaron lifetime of 13 μs. A method for observing photo-induced magnetization using optical pump-probe technique has been described.

A quadratic magneto-optical Kerr effect (QMOKE) of exceptionally high value, strong polar and longitu-dinal linear Kerr effects have been demonstrated in thin films of ferromagnetic (Eu,Gd)O and the parent compound EuO epitaxially grown on yttria-stabilized zirconia. At a photon energy of 1.85 eV, the effect reaches 1 deg in Eu0.97Gd0.03O exceeding the reported values of giant QMOKE by an order of magnitude. It is demonstrated that the QMOKE in (Eu,Gd)O enables detailed optical studies of the in-plane magnetic anisotropy of the film. The observed giant QMOKE may be employed for the development of vectorial sensors of weak magnetic fields. (C) 2020 Elsevier Ltd. All rights reserved.

We have produced a sample of 58 edge-on spiral galaxies at redshifts z ~ 1 selected in the Hubble Ultra Deep Field. For all galaxies we have analyzed the 2D brightness distributions in the V606 and i775 filters and measured the radial (hr) and vertical (hz) exponential scale lengths of the brightness distribution. We have obtained evidence that the relative thickness of the disks of distant galaxies, i.e., the ratio of the vertical and radial scale lengths, on average, exceeds the relative thickness of the disks of nearby spiral galaxies. The vertical scale length hz of the stellar disks of galaxies shows no big changes at z = 1. The possibility of the evolution of the radial scale length hz for the brightness distribution with redshift is discussed.

We present a simple semiclassical model to sustain that in europium chalcogenides (EuX), Faraday rotation (FR) in the transparency gap is proportional to the magnetization of the sample, irrespective of the material’s magnetic phase, temperature, or applied magnetic field. The model is validated by FR and magnetization measurements in EuSe in the temperature interval 1.7–300 K, covering all EuSe magnetic phases (paramagnetic, antiferromagnetic type I or type II, ferrimagnetic, and ferromagnetic). Furthermore, by combining the semiclassical model with the explicit electronic energy structure of EuX, the proportionality coefficient between magnetization and FR is shown to be dependent only on the wavelength and the bandgap. Due to its simplicity, the model has didactic value; moreover, it provides a working tool for converting FR into magnetization in EuX. The possible extension of the model to other intrinsic magnetic semiconductors is discussed.

We demonstrate that light resonant with the band gap forces the antiferromagnetic semiconductor EuSe to enter ferromagnetic alignment in the picosecond timescale. A photon generates an electron-hole pair, whose electron forms a supergiant spin polaron of magnetic moment of nearly 6000 Bohr magnetons. By increasing the light intensity, the whole of the illuminated region can be fully magnetized. The key to the novel large photoinduced magnetization mechanism is the huge enhancement of the magnetic susceptibility when both antiferromagnetic and ferromagnetic interactions are present in the material and are of nearly equal magnitude, as is the case in EuSe.

We explore a thermal mechanism of changing the anisotropy by femtosecond laser pulses in dielectric ferrimagnetic garnets by taking a low symmetry (YBiPrLu)3(FeGa)5O12 film grown on the (210)-oriented Gd3Ga5O12 substrate as a model media. We demonstrate by means of spectral magneto-optical pump-probe technique and phenomenological analysis, that the magnetization precession in such a film is triggered by laser-induced changes of the growth-induced magnetic anisotropy along with the well-known ultrafast inverse Faraday effect. The change of magnetic anisotropy is mediated by the lattice heating induced by laser pulses of arbitrary polarization on a picosecond time scale. We show that the orientation of the external magnetic field with respect to the magnetization easy plane noticeably affects the precession excited via the anisotropy change. Importantly, the relative contributions from the ultrafast inverse Faraday effect and the change of different growth-induced anisotropy parameters can be controlled by varying the applied magnetic field strength and direction. As a result, the amplitude and the initial phase of the excited magnetization precession can be gradually tuned.