Structure and morphology of epitaxial [Fe/Cr](30 )multilayers with ultrathin Fe layers (nominally 0.12 nm and 0.08 nm) have been investigated by X-ray reflectivity, synchrotron Mo center dot ssbauer spectroscopy at low temperature and grazing-incidence small angle X-ray scattering (GISAXS). The films demonstrate Kondo-like behavior of electrical resistivity. The GISAXS patterns reveal their cluster-layered structure. The observed side maxima give the information about the sizes and distances between lateral inhomogeneities. Mossbauer reflectivity spectra measured below the critical angle of the total reflection support the existence of the cluster-layered structure of the samples. Magnetic hyperfine field distributions show that largest number of 57Fe atoms is situated in interfaces of iron clusters and their number increases in the thinnest films.

The possibility of the existence of forbidden Bragg reflections in Mössbauer reflectivity, which are caused by the influence of interfaces on the specular reflection, is demonstrated. The calculations show that the measurement of Mössbauer spectra using forbidden reflections provides a fundamental opportunity to study interfaces selectively.

The magnetic properties of ultrathin single-crystal Y 57 FeO 3 orthoferrite films have been studied by Mössbauer reflectometry. Mössbauer spectra were measured using the ESRF synchrotron in the reflection geometry. As the temperature changes from 3.6 to about 773 K, the splitting of the Zeeman sextet in the spectra successively decreases and, simultaneously, a quadrupole doublet appears in them, which indicates the development of a magnetic phase transition. From the temperature dependences of the magnetic hyperfine field B hf for the main orthorhombic Y 57 FeO 3 phase, Néel temperatures equal to T N ≈ 593, 562, and 567 K and the critical parameter values equal to β ≈ (0.28–0.3) ± 0.02 are determined in films with thicknesses of 28, 6.5, and 4 nm, respectively. An analysis of changing ratio of the line intensities in the Zeeman sextet with temperature makes it possible to trace the successive rotation of the direction of the antiferromagnetic axes in Y 57 FeO 3 toward the surface plane with an increase in the temperature and a decrease in the film thickness.

Appearance of the refraction effects and Faraday rotation of the plane of polarization of linearly polarized X rays has been analyzed for transmission and reflection at grazing incidence angles for a resonant film including the X-ray magnetic or Mössbauer scattering. It is shown that, when the magnetization is oriented along the radiation beam direction, magnetic additives to the susceptibility do not affect the phase shifts between the waves reflected from the surface and the substrate; however, they induce “orthogonal polarization” in the reflected beam, which corresponds to rotation of the plane of polarization. Rotation of the plane of polarization is maximum for the critical angle of total external reflection; it is characterized by an oscillating dependence on the grazing angle, which can be used in future to vary the polarization state of X-ray beams.

This work demonstrates the use of polarization analysis of reflected radiation to reveal the contributions from magnetically ordered phases in poorly resolved Mössbauer spectra obtained with $$\pi$$ -polarized radiation from the Synchrotron Mössbauer Source. The study was carried out for the cluster-layered structure [ $${}^{57}$$ Fe (0.08 nm)/Cr (1.08 nm)] $${}_{30}$$ . As a result, it was shown that only 16 $$\%$$ of iron atoms are ferromagnetically ordered, while the remaining iron atoms are in the spin glass state.

Polarization analysis of the reflected radiation has been performed in Mossbauer reflectivity measurements with a Synchrotron Mossbauer Source (SMS). Effective pi ->sigma' polarization selection is attained with LiF crystal ((6 2 2) 90 degrees-reflection for 14.4 keV radiation, angular acceptance similar to 100 '') capable of high pi ->pi' suppression. Basic features of the reflectivity with the rotated pi ->sigma' polarization are revealed in the experiment with the [Fe-57(10 ML)/V(20 ML)](20) multilayer. Selection of pi ->sigma' polarization component in Mossbauer reflectivity allows to exclude nonresonant electronic scattering, besides Mossbauer pi ->sigma' reflectivity spectra (R-spectra) contain only contributions from magnetized along the beam ferromagnetic phases. The antiferromagnetic iron oxides do not contribute to pi ->sigma' R-spectra (dichroic component is compensated). Therefore, in the Mossbauer reflectivity experiment supplemented by polarization analysis the data interpretation becomes more certain and gives information about depth position for ferromagnetic layers selectively. With this new technique we locate antiferromagnetic iron phases in the very top layer of [Fe-57(10 ML)/V(20 ML)](20) multilayer and ascertain the ferromagnetic ordered iron layers in the remaining part of the structure. This new approach in Mossbauer reflectivity has interesting perspectives for investigations of hyperfine interactions for iron complexes on the surface, ultrathin layers and multilayers with complicated magnetic structures.

Mössbauer reflectivity spectra measured for the [Fe(3.0 nm)/Cr(1.2 nm)]10 structure in the half-order Bragg peak, which corresponds to the doubling of the period, have revealed the formation of a canted antiferromagnetic structure under the action of an external magnetic field of $${{B}^{{{\text{ext}}}}} = 0.06$$ Т applied perpendicular to the scattering plane. This result certainly follows from the appearance of the second and fifth lines in the Mössbauer sextet, which should be suppressed for any symmetric orientation of the magnetic hyperfine field in two 57Fe layers in one magnetic period. The experiment involves a polarization analysis of the reflected beam and shows that this new approach simplifies the form of angular dependences and reflectivity spectra, since it eliminates the interfering contribution of nonresonant scattering, and improves the reliability of the data interpretation.

An extension of the exact X-ray resonant magnetic reflectivity theory has been developed, taking into account the small value of the magnetic terms in the X-ray susceptibility tensor. It is shown that squared standing waves (fourth power of the total electric field) determine the output of the magnetic addition to the total reflectivity from a magnetic multilayer. The obtained generalized kinematical approach essentially speeds up the calculation of the asymmetry ratio in the magnetic reflectivity. The developed approach easily explains the peculiarities of the angular dependence of the reflectivity with the rotated polarization (such as the peak at the critical angle of the total external reflection). The revealed dependence of the magnetic part of the total reflectivity on the squared standing waves means that the selection of the reflectivity with the rotated polarization ensures higher sensitivity to the depth profiles of magnetization than the secondary radiation at the specular reflection condition.

The influence of electric field in the chemical synthesis of polyaniline on the surface of sulfonated cation-exchange membranes on their structure and properties has been investigated. By using standard contact porosimetry, it has been found that surface modification of heterogeneous membranes with polyaniline, both in static conditions and in an external electric field, does not significantly affect the distribution of water over the effective pore radii and binding energies. It has been shown that the structural heterogeneity of the ion-exchange membrane, rather than the aniline polymerization conditions, has a more significant effect on the morphology of the polyaniline layer on its surface and, hence, on the electrotransport properties. A decrease in the electrical conductivity of the composites obtained with an increase in the quantity of electricity passed during the synthesis of polyaniline on their surface has been revealed. Based on the analysis of the current–voltage characteristics of the samples and their electrical conductivity, the conditions for obtaining materials with the most pronounced asymmetry of the electrotransport properties have been determined.

Mössbauer reflectivity experiment with polarization selection are reported. The use of the LiF polarization analyzer allows us to get the π→σ’ peak on the reflectivity curve at the critical angle and Mössbauer π→σ’ reflectivity spectra of reasonable quality at the critical angle and also at the Bragg angles of superlattice. The impressive difference of the reflectivity spectra measured near the critical angle with and without polarizations analysis is observed for [57Fe10/V10]20 multilayer characterizing by the ferromagnetic interlayer coupling. The combined fit of the whole set of spectra measured at different angles reveals the existence of antiferromagnetic Fe oxide phases in the top three bilayers. The experiment demonstrates benefits of the Mössbauer reflectivity with polarization analysis in ultrathin surface layer investigations.

Grazing Incidence Small Angle X-ray Scattering (GISAXS) has been used for characterization of a cluster structure of the [Fe/Cr](30) multilayer with ultrathin iron layers. The experiment was performed at the "Langmuir" station of the Kurchatov Center of Synchrotron Radiation and Nanotechnology. Experimental GISAXS image has shown the side satellites and the Bragg peak revealing the existence of density inhomogeneities with an average lateral distance of similar to 19 nm periodically repeated along depth. The modelling of the obtained image has been done in the DWBA approximation. It has been shown that for the wavelength used in the experiment (0.0951 nm) it is not possible to distinguish if the inhomogeneities exist in the Fe or in the Cr layers due to the small optical contrast between Fe and Cr layers. However, as it has been demonstrated by model calculations, in the case of the enhanced optical contrast (e.g. for the wavelength corresponding to the L-3 edge of Fe) the x-ray standing waves allow ones to select the cases of inhomogeneities in the Fe or in the Cr layers: the simulated GISAXS patterns are rather different for these two cases.

Nuclear resonance reflectivity from a [Dy 19 Gd 19 ] × 20 superlattice has been measured utilizing the 25.652 keV nuclear level of 161 Dy. The measured time spectra of nuclear resonance reflectivity make it possible to reveal the variation of the hyperfine magnetic field B hf on dysprosium nuclei in the temperature range of 4–110 K and to determine the relaxation time of the hyperfine field, using the decay speed-up of the excited state of 161 Dy nuclei.

The dichroic effect (“rotated” polarization) in the reflectivity from a magnetically ordered sample is experimentally studied at the station PHASE of the Kurchatov Synchrotron Radiation Source. The experiments are performed for the Gd 0.23 Co 0.77 film, which has a compensation temperature T comp ≈ 433 K, using linearly polarized radiation of the photon energy of 7930 eV ( L 2 absorption edge of gadolinium) at room temperature. The developed theory of reflectivity accounted for the magnetic contributions to the scattering amplitude predicts the appearance of a peak for the orthogonal (to the incident polarization) polarization of the reflected radiation near the critical angle of the total external reflection. The experiment reveals the significant difficulties because of the incomplete σ polarization of the synchrotron beam, the beam instability, and so on. Therefore, a rotated-polarization peak has been detected near the critical angle but at the limits of the measurement accuracy. In principle, our experimental technique could be an alternative to circular polarization experiments, which are widely used at synchrotrons to study magnetic ordering. However, as we have shown, it makes high demands of the radiation source parameters.

We have studied the magnetization depth profiles in a [57Fe(dFe)/Cr(dCr)]x30 multilayer with ultrathin Fe layers and nominal thickness of the chromium spacers dCr 2.0 nm using nuclear resonance scattering of synchrotron radiation. The presence of a broad pure-magnetic half-order (1/2) Bragg reflection has been detected at zero external field. The joint fit of the reflectivity curves and Mossbauer spectra of reflectivity measured near the critical angle and at the "magnetic" peak reveals that the magnetic structure of the multilayer is formed by two spirals, one in the odd and another one in the even iron layers, with the opposite signs of rotation. The double-spiral structure starts from the surface with the almost antiferromagnetic alignment of the adjacent Fe layers. The rotation of the two spirals leads to nearly ferromagnetic alignment of the two magnetic subsystems at some depth, where the sudden turn of the magnetic vectors by ~180 deg (spin-flop) appears, and both spirals start to rotate in opposite directions. The observation of this unusual double-spiral magnetic structure suggests that the unique properties of giant magneto-resistance devices can be further tailored using ultrathin magnetic layers.

Mössbauer reflectivity spectra and nuclear resonance reflectivity (NRR) curves have been measured using the Synchrotron Mössbauer Source (SMS) for a [57Fe/Cr]30 periodic multilayer, characterized by the antiferromagnetic interlayer coupling between adjacent 57Fe layers. Specific features of the Mössbauer reflectivity spectra measured with π-polarized radiation of the SMS near the critical angle and at the `magnetic' maximum on the NRR curve are analyzed. The variation of the ratio of lines in the Mössbauer reflectivity spectra and the change of the intensity of the `magnetic' maximum under an applied external field has been used to reveal the transformation of the magnetic alignment in the investigated multilayer.

Nanostructured epitaxial [57Fe(1.2 Å)/Cr(10.5 Å)]30 multilayer with ultrathin Fe layers, demonstrated Kondo-like behavior, has been investigated by means of the nuclear resonance reflectivity at low temperatures (down to 4 K) in magnetic fields up to 4 T. We detected the beginning of the magnetic phase transition at 150 K which correlates with the minimum on the electrical resistivity curve. The determined magnetic hyperfine field distribution P(Bhf) indicates an inhomogeneity of the iron environments. When we apply the very high external magnetic field up to 4 T, it aligns Bhf(i) along the direction of the external field only partially. Also it has been noticed that Bhf(i) orientations depend on the magnetic pre-history.