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The possibility of forming thin-film two-phase compositions CdxPb1-xS/Cd1−δS using chemical bath deposition from aqueous media with adding various cadmium salts has been demonstrated. The crystal structure, chemical composition, morphology, and the band gap were studied by the X-ray diffraction, scanning electron microscopy, elemental analysis, Auger and Raman spectroscopy, and diffuse reflectance measurements. The formation of a CdxPb1−xS/Cd1−δS substitutional solid solution phase in well-faceted crystallites on the substrate of an X-ray amorphous CdS phase was experimentally shown. The observed difference in the composition of the films deposited with adding different cadmium salts is the result of the effect of the nucleophilicity of the anionic component of these salts on the kinetics of thiourea decomposition. The results demonstrate the possibility of forming thin-film two-phase compositions or heterostructures on the base of cadmium and lead sulfides in one technological stage using chemical bath deposition, which can be important for the creation of solar cells.

Herein, we describe the nonlinear processes for the formation of thin films of the PbS-CdS system using chemical bath deposition with a gradual change in the cadmium nitrate content in the reaction mixture. The morphology of films was studied via scanning electron microscopy and atomic force microscopy. The mechanism for the formation of thin-film compounds can be considered as cluster-particle aggregation (diffusion-limited aggregation). X-ray diffraction confirmed the formation of single-phase layers of substitutional B1-type CdxPb1-xS solid solutions (space group Fm3[combining macron]m) when the concentration of cadmium nitrate in the reaction bath increased up to [Cd(NO3)2] = 0.08 M. The maximum cadmium content in CdxPb1-xS solid solutions was determined to be x = 0.094. At the concentration of [Cd(NO3)2] = 0.10 M, a two-phase film was formed, where the film consisted of crystallites of cubic CdxPb1-xS with x = 0.071 (lower compared to the film obtained at [Cd(NO3)2] = 0.08 M) and fine-crystalline hexagonal B4-type Cd1-δS (space group P63mc). The texture of grains forming films was observed; where a predominant orientation with the (111) plane along substrate in PbS changed to the (200) plane in CdxPb1-xS films, the portion of (200) oriented grains increased with an increase in cadmium nitrate content up to [Cd(NO3)2] = 0.08 M, and at 0.10 M of cadmium nitrate, a radical change in the type of texture to the (111) type occurred. The concentration [Cd(NO3)2] = 0.10 M is called the critical concentration, where under this condition, the deposition process occurs due to the excess Gibbs energy. The higher cadmium content x in films determined by the energy-dispersive X-ray analysis and Auger spectroscopy compared with that estimated from the crystal lattice parameter is associated with the presence of an additional amorphous CdS phase formed as a sublayer distributed in intercrystalline spaces and island formations. Optical studies showed a nonlinear change in the band gap (Eg) of obtained films from 0.53 to 0.76 eV, whereas at the critical cadmium salt concentration (0.10 M), two crystalline phases with Eg equal to 0.73 and 2.47 eV were observed.

Polycrystalline films of PbS:Fe are obtained via hydrochemical deposition from an ammonia-citrate bath containing 10−5 to 7 × 10−3 M of FeCl2 doping additive. The films’ morphology is studied along with their structural and optical properties. An increase in the lattice parameter of PbS doped up to 5 × 10‒3 M testifies to the interstitial position of Fe2+ ions, while a subsequent reduction in the lattice parameter is due to some of the lead ions in the PbS crystal lattice being replaced with iron ions of a smaller radius. Doping with iron ions produces impurity absorption bands in the optical absorption spectra of PbS:Fe films. Rearrangement of the zone structure of lead sulfide near the edge of the band gap is observed in a film obtained from a solution containing 5 × 10−3 M FeCl2. The change in the zone structure is due to the lead ions in the PbS lattice being replaced with iron ions.

Evolution of the morphology, composition, structural characteristics (lattice constant, microstrains, texturing), and optical and photoelectric properties of PbS films produced by chemical bath deposition in the presence of ammonium iodide and strontium or barium chlorides at a concentration up to 5 mM is studied. According to the data of energy dispersive X-ray analysis, the content of strontium in the PbS films is 0.4–0.7 at %, whereas the content of barium is beyond the determination error. The size of the particles forming the films varies from ~200 to ~400 nm, and the size distribution of the particles is monomodal. The introduction of NH4I and SrCl2 or BaCl2 into the reactor retains the B1 cubic structure of lead sulfide, but gives rise to an unsteady change in the lattice parameter, which is due to the creation of vacancy-type or interstitial ion defects. The introduction of salts of strontium or barium does not influence the band gap, but changes the intensities of the impurity absorption bands deep in the band gap or near the bottom of the conduction band. The dependences of the volt–watt sensitivity of the films on the content of salts of strontium and barium are of an extreme character and show maxima at 0.05 and 0.1 mM, respectively.

This paper considers mechanophysical methods (shear under pressure and explosive loading) developed for producing high-density optical nanoceramics based on some oxide magnetic semiconductors and their optical properties. Advantages of these methods are the simplicity of implementation, a combination of nano-grinding and compaction of material in a single process, obtaining high-density (∼99%) stable materials, and the absence of external impurity. It is shown that copper oxide nanoceramics can be used as solar energy absorbers and iron-yttrium garnet nanoceramics as an optical element in electromagnetic radiation modulators.

The absorption spectra of cobalt-doped anatase TiO2 nanopowders in the infrared and visible ranges have been studied after various oxidative and reductive treatments. The annealing leads to the appearance of the Drude-like contribution in the infrared region and significant change in the absorption in an visible range due to the formation of defects of the oxygen-vacancy-type and Ti3+ ions. The observed additional contribution in the absorption spectra of TiO2:Co nanopowders as compared to the spectra of undoped powders is ascribed to the d–d transitions in ions Co2+. The change in the absorption related to cobalt after annealing is explained by a change in the local environment of Co ions from the octahedral to the tetrahedral environment.

Polycrystalline lead-sulfide (PbS) films doped with calcium are synthesized on sitall and glass substrates by chemical bath deposition with the use of thiocarbamide and a CaCl2 additive at concentrations of up to 5 mM. Introduction of the CaCl2 additive into the reaction solution greatly prolongs the induction period of the process of synthesis. The thicknesses of the PbS and PbS(Ca) films are, correspondingly, 200 and 150 nm at an average crystallite dimension of ~100 nm. The maximum calcium content in the films is 0.06 at % for layers on sitall substrates and 0.11 at % for layers on glass substrates. Doping with calcium does not influence the crystal structure of lead sulfide (the cubic B1 structure, space group Fm3 $$\bar {m}$$ ) but brings about an increase in the crystal-lattice period from a = 0.59343(2) nm to a = 0.59413(1) nm, an increase in microstrains, and partial ordering of the crystallites forming the film. Upon the introduction of calcium, the band gap decreases from Eg = 0.40 eV at 295 K (0.38 eV at 90 K) to Eg = 0.38 eV (0.37 eV). The introduction of up to 5 mM of CaCl2 into the reaction mixture increases the voltage–power sensitivity of the films by a factor of ~1.7, which is attributed to oxygen-containing compounds formed in the films as a result of the increase in the induction period of the process of synthesis.

Double manganite PrBaMn2O6 with ordered alternate stacking of PrMnO3/BaMnO3 layers attracts a special interest due to presence of two magnetic phase transitions close to room temperature; that makes it perspective magnetocaloric and magnetoresistive material. Besides the magnetic phase transition, the structural transition accompanied with the elongation of the a-axis and the contraction of the c-axis was experimentally detected. The origin of structural phase transition is studied by X-ray powder diffraction, X-ray photoelectron spectroscopy (XPS), IR absorption spectroscopy, magnetometry and dynamical mean-field theory (DMFT) for electronic structure calculations. It is found that the structural phase transition is caused by splitting of eg-doublet states due to the tendency towards orbital ordering at the metal-insulator phase transition.

The calcium-doped PbS films are produced by using the chemical bath deposition method (CBD) on glass and sitall substrates. The influence of the calcium doping on the structural, morphological and optical properties of these films is studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), optical spectroscopy, and energy dispersive X-ray spectroscopy (EDX). The lead sulfide films have cubic structure (B1). The inclusion of calcium in the crystal structure of PbS up to 0.11 at. % is confirmed by the elemental, radiographic and energy-dispersive analyzes. The band gap Eg in the undoped PbS film is estimated as 0.40 ± 0.01 eV at 295 K and 0.38 ± 0.01 eV at 90 K and decreases with calcium doping by ∼0.02 eV. It is shown that doping of lead sulfide films with calcium by adding CaCl2 up to 5.0 mmol/l results in the increase in the photoresponse to IR radiation in 1.7 times.

For double manganites PrBaMn2O6 with different degree of A-site ordering, magnetic and optical properties in near-IR range were studied. Full ordered manganite is characterized by antiferromagnetic state at low temperatures; magnetic phase transition from antiferromagnetic to ferromagnetic state occurs near TN = 262 K and to paramagnetic state near TC = 305 K. Partially disordered manganite consists of few fractions with different state of A-site ordering and shows the transition from ferromagnetic state to paramagnetic one at 190 K. For disordered manganite weak ferromagnetic contribution is observed below 130 K. The optical density spectra and the temperature dependences of light transmission indicate a change in behavior of the charge carrier system (metal–insulator transition) near the magnetic phase transitions. The magnetotransmission effect was measured for the first time in double manganites PrBaMn2O6. Spectral dependence of magnetotransmission lets associate this effect with an increase in the fraction of delocalized charge carriers when a magnetic field is applied.

Films of cubic substitutional CdxPb1−xS solid solutions have been synthesized by the chemical bath deposition with varying cadmium acetate salt Cd(CH3COO)2 in the reaction mixture within 0.01–0.08 mol/l on quartz substrates. The crystal structure, chemical composition and morphology were studied by the X-ray diffraction, scanning electron microscopy, elemental analysis, Auger spectroscopy, and Raman spectroscopy, as well as the evolution of the optical and photoelectric properties was determined. The thickness of the deposited films changes from ~ 0.4 to ~ 1.0 μm, and the content of cadmium x in the CdxPb1−xS solid solution varies from 0.036 to 0.090. All the CdxPb1−xS films have B1 crystal structure (NaCl type), but differ in the morphology (the size, form and predominant orientation of the particles forming the films). Forming the substitution solid solution is confirmed by the shift of the Raman lines at 72 and 134 cm−1 toward higher frequencies. The optical band gap determined from the absorption spectra varies from 0.46 to 0.70 eV. The dependences of the photoresponse value (volt-watt sensitivity) and the dark resistance on cadmium acetate concentration in the solution are represented.

Thin polycrystalline films of cubic lead sulfide doped with iron (II) PbS:Fe have been synthesized by chemical bath deposition from aqueous solutions of lead acetate, sulfidizing agent, and complexing and alkaline agents in the presence of FeCl2 salt in the concentration range from 10−5 to 7 × 10−3 M. At the iron (II) chloride concentration lower than [FeCl2] = 5 × 10−3 M, the crystal lattice parameter of PbS increases indicating the interstitial position of Fe2+ ions. At [FeCl2] = 5 × 10−3 M, the substitution of iron ions for lead ones is found. The absorption spectra show that on increasing FeCl2 concentration in the reaction bath up to 10−3 M, the band gap of the synthesized PbS:Fe films hardly changes (Eg∼0.4 eV); only the growth of the impurity bands near the absorption edge is observed. At [FeCl2] = 5 × 10−3 M, the blue shift of the absorption edge occurs, the band gap increases to 0.58 eV, and the impurity absorption band shifts toward the higher energies. Cooling the films in the magnetic field influences the intensity of the impurity absorption bands associated with iron when Fe2+ ions are located in interstitial position. The observed changes in the optical spectra are explained by the difference in the band structure and the position of the impurity levels when Fe2+ ions are at the interstices or in the Pb ions position.

The anisotropy of reflection spectra is studied for the single crystals of layered EuBaCo1.9O5.36 cobaltite within the temperature range of 80–295 K. The results involving the comparison with the magnetic and transport characteristics are analyzed. In the reflection spectra from the (001) and (120) planes measured at T = 295 K (below the temperature corresponding to the transition to the semiconducting state, T MI = 345 K), a contribution from itinerant charge carriers has been revealed. This contribution is associated with the existence of an inhomogeneous charge state. In the reflection spectrum from the (120) plane, the contribution from itinerant charge carriers holds down to T = 80 K. The difference between the reflection spectra from different planes and different characters of their changes with the temperature are attributed to the anisotropy of the clusters with itinerant charge carriers.

The magnetic, transport, optical, and elastic properties of the electron-doped manganites CaMn1-xMxO3 with Mn-site doping (M=Mo or W, x≤0.20) are studied and the results are compared with those of Ca-site substituted manganites with the same Mn3+ concentration. If Mn3+ concentration is lees than 10%, the charge carriers' localization due to lattice distortions in the Ca-site doped samples is stronger than the localization caused by magnetic dilution in the case of Mn-site substitution. At higher Mn3+ concentration, the magnetic dilution plays a key role.

Influence of the substitution of Hg by Cd on Kerr effect, magnetoreflection, and magnetotransmission of unpolarized light for Hg1-xCdxCr2Se4 (0≤x≤1) single-crystals is studied. The changes in the magnetooptical properties of the ferromagnetic spinels are shown to occur in compositions with x>0.1. The giant values of magnetooptical effects in Hg1-xCdxCr2Se4 spinels can be used in the magnetooptoelectronics.

The optical density spectra D(hω) of BiFe0.5Co0.5O3 films with thickness d = 230 and 1400 nm on LaAlO3 substrate were studied in the infrared range from 0.09 to 1.65 eV in unpolarized and linear polarized light at room temperature and at T = 80 K in the magnetic field of 4.5 kOe and without the field. The absorption bands at hω ~0.2 and ~0.7 eV are revealed in the D(hω) spectra recorded in unpolarized light and attributed to combination of two-phonon and two-magnon absorption and to d–d transitions in Fe or Co ions, respectively. In the D(hω) spectra of BiFe0.5Co0.5O3 film with d = 230 nm recorded in linear polarized light, the additional bands in the range of 0.3 eV–1.0 eV are found and explained by the nonuniform charge state due to the existence of weakly conductive electric domains and domain walls with higher conductivity and by the scattering of the light on the domains. The position of the bands in the optical density spectra in polarized light D ⊥(hω) and D ∣∣(hω) depends on the direction of the magnetic field relative to the film and on the temperature, which is explained by the change of the electric domain sizes. The revealed dependence of the optical properties on the magnetic field direction allows recommending BiFe0.5Co0.5O3 films as new functional magneto-optical material.

The magnetic, transport and elastic properties of CaMn 0.96 Mo 0.04 O 3 polycrystal are reported. The magnetic data of the paramagnetic region point to the magnetic polarons. The transition from the paramagnetic state into the antiferromagnetic state of G-type occurs near 93 K, the crystal orthorhombic structure being unchanged. The transition from the paramagnetic orthorhombic phase into the C-type antiferromagnetic monoclinic phase is revealed at about 130–140 K, the transition taking place in small regions of the sample.

Conventional magneto-optical Kerr and Faraday effects are widely used to solve many urgent problems in various fields of physics and technique. However, in view of the small magnitude of these effects (related to their relativistic origin), it is necessary to search for ways to enhance known magneto-optical effects and materials, as well as to reveal new (stronger) ones. In this study, we consider the effects of magnetotransmission and magnetoreflection of unpolarized light (of large magnitude), which were revealed in single crystals, films, and structures based on magnetic semiconductors. Some physical problems, calling for further study, are discussed, and a possibility of applying these effects to design different magneto-optical devices is demonstrated.

The reflectance, the optical density, and the optical conductivity spectra of CaMn1 − xMoxO3 (x ≤ 0.07) polycrystals are studied over a wide spectral region. The substitution of Mo6+ ions for Mn4+ ions leads to a strong decrease in the first high-energy phonon band, which is related to vibrations in the MnO6 octahedron. The appearance of band-type charge carriers is detected in CaMn1 − xMoxO3 with x ≤ 0.04, and carrier localization is observed in CaMn0.93Mo0.07O3. This localization increases at T < 160 K, i.e., during the transition from the paramagnetic to the antiferromagnetic state with orbital ordering and a monoclinic structure. The optical conductivity spectrum of CaMn0.93Mo0.07O3 exhibits a strong shift of fundamental absorption bands, which is associated with a change in the band structure because of a decrease in the splitting of the 3d levels of Mn in the crystal field.

The magnetic properties of nanopowders of Nd0.5Sr0.5MnO3 manganite, obtained by ball milling method, and IR magnetotransmission (the relative change in transmission of infrared radiation in a magnetic field) of composites based on the nanopowders are studied and compared with properties of Nd0.5Sr0.5MnO3 single crystal and coarse grain powder. The strong decrease of the magnetization at transformation of the single crystal to coarse grain powder is associated with the martensitic nature of the charge-ordered state (CO), TCO∼150 K. With a further decrease of particles size the magnetization decreases sharply above 150 K and is less significant in the region below 150 K, where a plateau in temperature dependence of magnetization and magnetotransmission takes place. The plateau is explained by modification of the manganite properties at milling and associated with competition of the ferromagnetic and antiferromagnetic contributions in cores and surface of the nanoparticles and change in the degree of localization of charge carriers in the magnetic field. The high value of the magnetotransmission (up to 9%) in a wide temperature range for nanocomposites are promising for creation of magnetically controlled infrared optoelectronic devices.

Magnetic, transport and optical properties of the Ca0.85Eu0.15MnO3 single crystal are studied and discussed in comparison with the properties of polycrystalline sample. The magnetic data show existence the two magnetic phase transitions under cooling: the transition near 150 K occurs from the paramagnetic orthorhombic to C-type antiferromagnetic monoclinic phase with the charge/orbital ordering in some part of the crystal; and at 90 K the transition from the paramagnetic to G-type antiferromagnetic phase takes place in another part of the crystal with the orthorhombic structure. The magnetoresistance of the Ca0.85Eu0.15MnO3 single crystal has features at temperatures of these phase transitions. Differences in the properties of single crystal and polycrystalline sample with the same content of Eu are associated with the ordering of oxygen vacancies that appear under the crystal growth. The reflection spectra in infrared range confirm the existence of the electron conductivity in a narrow band at room temperature.

Nd0.52Sr0.48MnO3 − δ manganite films on LaAlO3 substrate exhibit a large negative magnetotransmission [(tH − tH = 0)/tH = 0 ≈ −14%] at a wavelength of 8.8 μm in a magnetic field of H = 8 kOe and a large negative magnetoresistance [(ρH − ρH = 0)/ρH = 0 ≈ −50%] in a field of H = 10 kOe at a temperature T = 225 K. The influence of oxygen vacancies in the manganite lattice on the magnitude of observed effects is discussed. The high values of magnetotransmission and magnetoresistance allow Nd0.52Sr0.48MnO3 films to be recommended for use in magnetic-field-controlled optoelectronic devices and in spintronics.

We present the results of the study of middle infrared absorption (MIR) and X-ray absorption (XAS) spectra of nanostructured CuO and Cu2O ceramics prepared by the high pressure torsion method from coarse-grain oxide powders. We have found that the MIR bands at ~140 meV in CuO and Cu2O nanoceramics are associated with the presence of Cu+ and Cu2+ ions, respectively. X-ray absorption spectra indicate an appearance of extra Cu2+ and Cu+ ions in nanoCu2O and nanoCuO ceramics, respectively.

The work is devoted to a review of magnetic, electrical, and optical properties of electron-doped manganites Ca1 − x Ln x MnO3 (Ln stands for rare-earth ions) at the concentrations of the doping ions x from 0 to 0.2. The main attention is paid to the data obtained using single crystals containing vacancies in both the anion and cation sublattices. The features of the multiphase state of the Ca1 − x Ln x MnO3 manganites (x < 0.2) are discussed.

Optical absorption of orthorhombic and hexagonal manganites RMnO3 (R= Pr3+, Gd3+, Sm3+, Eu3+, Ho3+, Tm3+, Er3+, and Yb3+) were studied in polarized light in the near- and mid-infrared range for the temperature range 80 - 300 K. Several spectral features associated with 4f-4f transitions of R3+ ions were found in the transparency window of RMnO3. Anisotropy of the absorption spectra in the range of multiplet 4f-4f transitions and changes in populations of the multiplet levels with temperature were observed.

Features of the optical properties of nanostructured strongly correlated oxides CuO, Y3Fe5O12, and FeBO3 in a wide range of energies, which includes both the fundamental absorption region, low-energy electron excitations, and phonon modes have been investigated by methods of optical spectroscopy. Absorption and reflection spectra, Raman spectra, and ellipsometry measurements are carried out on the samples of oxide nanostructured ceramics. High-density nanoceramics were prepared by shock-wave loading and high pressure torsion methods from coarse-grain oxide powders. Strong smearing of the fundamental absorption edge is revealed for all nanoceramics. Anomalous red shift of the absorption edge Eg is found in CuO nanooxide. The features of the optical functions in nanooxides of 3d-metals may be attributed to high defectiveness of nanooxides, peculiarities in the electronic structure of strongly correlated oxides and their tendency to electronic phase separation.

IR absorption and magnetic data for the titanium dioxide nanopowders are studied. Additional absorption in IR range is revealed in nanocrystalline TiO2 and Co-doped TiO2 after reducing annealing and explained by appearance of the oxygen vacancies and delocalised charge carriers. Increasing of the absorption in IR range after annealing of Co-doped TiO2 in vacuum (or decreasing of this contribution after annealing in air) correlates with arising (or vanishing) of ferromagnetic contribution. © 2018 The Authors, published by EDP Sciences. This work was supported by the Russian Scientific Foundation, Grant No. 16-12-10004.

The magnetic, electrical, and optical properties of Ca1 − xCexMnO3 (x≤0.12) manganite single crystals are investigated with the aim of revealing the specific features of the multiphase electronic and magnetic state as a function of the cerium concentration and the atmosphere used for growing single crystals. It is found that the concentration dependence of the low-temperature magnetization M(x) of the single crystals is shifted toward the high-concentration range as compared to the corresponding dependence of the polycrystals, which is explained by the predominant cation deficiency. The electrical resistivity and the reflection spectra of the single crystals in the infrared spectral range indicate that charge carriers exhibit a band nature at temperatures close to room temperature. The temperature dependence of the electrical resistivity of the single crystal with x = 0.08, which has the maximum magnetization in the studied series of Ca1 − xCexMnO3 compounds, unlike polycrystals, exhibits a metallic behavior over the entire temperature range. The G-type antiferromagnetic phase with the Neel and Curie temperatures TN(G) = TC = 100 K is characterized by maxima of the electrical resistivity ρ and the magnetoresistance Δρ/ρ = |(ρ0 − ρH)/ρ0| = 38% in the magnetic field H = 90 kOe. The magnetoresistance Δρ/ρ of the single crystals at cerium concentrations x = 0.10 and 0.12 with variations in temperature exhibit three specific features: near the temperature of charge ordering Tco, near the temperature of the magnetic phase transition to the C-type antiferromagnetic phase TN(C), and near the temperature of the phase transition to the magnetic charge-ordered phase TN(MCO). An anomalous temperature dependence of the magnetization is revealed for a single crystal with x = 0.10 grown in oxygen at a pressure of 5 atm, which is explained by the presence of regions with hole conductivity due to cation deficiency. The inhomogeneous electronic and magnetic state is associated with the interrelation of the charge, orbital, and spin orderings.

High efficiency of the approach combining the study of IR transmission and resistivity for detecting phase separation in the electron subsystem of lanthanum manganites has been demonstrated. Comparison of the magnetotransmission, magnetoresistance, and Kerr effect makes it possible to reveal the phase separation in the magnetic subsystem of manganites.

We demonstrate that the colossal magnetoresistance (CMR) manganites doped with the monovalent cations of the large ionic radius A (A = Na+, K+, Ag+) reveal enhanced sensitivity of the electrical resistance to the magnetic field near the room temperature. The main obstacle to their practical application is severe difficulty of the synthesis, in particular, that of the thin films because of the high volatility or low thermal stability of the oxides of these doping elements. But the preparation of the films in two steps allows for the materials with the superior CMR characteristics. At the first step, epitaxial single phase precursor La1−xAyMnO3 (0.3 ≥ x > y) is formed on the single crystal substrate due to the epitaxial stabilization by the single source MOCVD (metalorganic chemical vapor deposition) using thd-complexes. The second step is the isopiestic annealing with the powder mixture determining the high concentration of the volatile oxide in the gas phase resulting in the saturation of La1−xAxMnO3 (x = y) films by the gas phase transport. The film transformations are studied with XRD and HREM. The high magnetoresistance MR and magnetotransmission MT with the linear magnetic field (H) dependence near the room temperature (dMR/dH up to 45%/T, dMT/dH up to 15%/T) are reported.

Optical absorption in the bi-layered manganites La2 − 2xSr1 + 2xMn2O7 (x = 0.3 and 0.4) was studied and metallic clusters were revealed in the temperature range TC < T

Reflection spectra, resistivity, thermopower and the Hall effect of Ca 1− x La x MnO 3 (0.03⩽ x ⩽0.12) single crystals are studied. It is shown that the optical spectra are described by the Drude model. Concentration of the charge carriers is determined to be equal to doping ∼10 21 cm −1 . In contrast to lightly hole-doped manganites, in Ca 1− x La x MnO 3 conductivity has a band character. The optical effective mass m * of electrons and effective mass of density of states of the conduction band m d * are found to be about 2 – 3 m 0 and ∼ 10 m 0 , respectively. The width of the conduction band is estimated as ∼1 eV. The revealed difference between optical effective mass and effective mass of density of states is attributed to the anisotropic dispersion law and multivalley character of the conduction band.

The magnetic, transport, and optical properties of electron-doped Ca 1− x La x MnO 3− δ single crystals with x ⩽0.12 were studied. The magnetic measurements show that in single crystals with x = 0 and 0.05 the G-type AFM phase with weak FM component is realized and in crystals with x = 0.10 and 0.12 the G- and C-type AFM phases coexist. The C-type magnetic structure arises at less concentration of La than in polycrystalline samples as a result of oxygen vacancies being additional source of electrons. Under magnetic transitions in the G- and C-type phases, resistivity and magnetoresistance of the doped single crystals have anomalies. Optical absorption in IR range indicates formation of a charge gap in crystals with x = 0.10 and 0.12 at appearance of the C-AFM and monoclinic phase with orbital/charge ordering. By comparing optical and transport properties, heterogeneous electronic state and its relation with heterogeneous magnetic state are shown.

The high-energy edge of the transparency window in nanocrystalline copper monoxide (CuO) can be shifted to 0.6 eV (against 1.45 eV in single crystals). This shift is related to a modification of the shape of the fundamental absorption edge of CuO without any change in the refractive index. The obtained nanocrystalline CuO is recommended for use as a selective solar energy absorber.

A 0.1–0.15-eV displacement of the fundamental absorption edge in the optical absorption spectra of nanocrystalline oxide n-CuO (relative to the position of the fundamental absorption edge in the spectra of CuO single crystals) towards lower energies (red shift) is observed against the background of strong blurring. Nanocrystalline n-Cu2O exhibits a displacement of the fundamental absorption edge towards higher energies (blue shift) by approximately 0.35 eV. The size of crystallites in n-CuO and n-Cu2O ranges from 10 to 90 nm. The blue shift of the fundamental absorption edge of n-Cu2O is typical of classical wide-gap semiconductors and can be explained by size quantization upon a change in the particle size. The anomalous red shift of the fundamental absorption edge of the strongly correlated nanocrystalline oxide n-CuO can be attributed to the highly defective structure of n-CuO, anomalies in the electronic structure of strongly correlated compounds based on 3d metals, and their tendency to electronic phase separation with the formation of metal-like inclusions.

The magnetic, electrical, and optical properties of Ca1 − x LaxMnO3 − δ(x ≤ 0.12) manganite single crystals have been studied. The state with a spatially inhomogeneous electron distribution has been found. Interrelations between the electric and magnetic subsystems are analyzed. The obtained magnetic data show evidence for the formation of a G-type antiferromagnetic (G-AFM) phase with a spin-canted structure in the crystal with x = 0.05, for which the Curie and Neel temperatures are T C = T N(G) = 115 K. On cooling from the paramagnetic state, the crystals with x = 0.10 and 0.12 exhibit transitions from the paramagnetic to a C-type antiferromagnetic (C-AFM) phase in a part of the volume at T N(C) = 150 and 200 K, and from the paramagnetic to the G-type antiferromagnetic (G-AFM) phase in the remaining volume at T N(G) = 110 and 108 K, respectively. The onset of the C-type magnetic phase nucleation in crystals is observed at lower dopant (La) concentrations than in polycrystalline samples, which is explained by the deviation of single crystals from the stoichiometry with respect to oxygen. The magnetic phase transitions are manifested by anomalies in the electric resistance and magnetoresistance of doped crystals. An analysis of the electrical and optical properties of the samples shows evidence of (i) the formation of a charge energy gap in the C-AFM phase with retained paramagnetic metallic regions and (ii) the presence of ferromagnetic “metallic” droplets in the insulating G-AFM phase. The multiphase state of Ca1 − x LaxMnO3 − δ manganite single crystals featuring the coexistence of two magnetic phases, the regions with orbital/charge ordering, and the FM “metallic” droplets is related to a competition of exchange interactions by the superexchange and double exchange mechanisms.

The optical, magnetooptical, and electric properties of epitaxial (La1−xPrx)0.7Ca0.3MnO3 films (0≤x≤1) grown by MOCVD on LaAlO3 and SrTiO3 substrates were studied. It is shown that the decrease in the average cation radius resulting from isovalent substitution of the Pr for La ions brings about a lowering of the Curie temperature, the metal-insulator transition temperature, and the temperatures of the maxima in magnetotransmission (MT) and magnetoresistance (MR). These temperatures depend only weakly on the substrate type. Substitution of La by Pr does not change the shape of the spectral response of the transverse Kerr effect. For concentrations x≤0.50, the maximum values of the Kerr effect and of the MT vary insignificantly, which should be assigned to the existence of a singly connected ferromagnetic metallic region at low temperatures. In films with x=0.75, the presence of ferromagnetic metallic drops in an antiferromagnetic insulating matrix was revealed. The totality of the experimental data obtained suggest that nanoscopic magnetic and electronic nonuniformities exist both in films with a singly connected metallic region and in an x=1 film, which is an antiferromagnetic insulator.

The variations in the electronic structure and the evolution of phase separation as a result of creation of vacancies or excess of lanthanum in lanthanum manganites are studied on the basis of analysis of optical and magnetic properties of LaxMnO3 epitaxial films (0.83≤x≤1.10) in the fundamental absorption range. The Kerr effect, the temperature dependences of resistivity, optical density, and magnetoabsorption of light indicate the charge and magnetic phase separation in the films. The fine structure observed in the spectrum is attributed to spectral overlapping of electron transitions with charge transfer and geometrical resonances reflecting an inhomogeneous nanoscopic structure of the films, which strongly depends on stoichiometry and stresses emerging during film deposition. It is shown that, in contrast to bulk polycrystals, the gradient of stresses over the film thickness significantly affects the phase separation in the films.

The optical absorption spectra of LaMnO3 single crystals, pure and slightly doped with Ce and Sr (7%), were studied in the middle IR region. Ellipsometry measurements were performed in the visible region to determine real and imaginary permittivity parts. The energies of the onset of indirect transitions in LaMnO3 at 293 and 80 K were found to be 0.30 and 0.40 eV, respectively. Impurity absorption bands corresponding to transition in hole and electron clusters were observed. The anomalous temperature dependence of IR absorption was explained by the existence of conducting droplets in the insulated doped crystal matrices at temperatures below the temperature of the appearance of a ferromagnetic contribution. The existence of such a contribution was proved by studying the equatorial Kerr effect. Because of the separation of phases, manganites slightly doped by a nonisovalent admixture can be treated as optically nonuniform media whose properties are similar to those of a composite system with metallic inclusions.

A new approach to the study of phase separation in lanthanum manganites is proposed based on the combined investigation of their optical and magnetooptical characteristics providing information about the conducting and ferromagnetic regions, respectively. Effects of the 18O isotope substitution for 16O in the epitaxial films of (La0.5Pr0.5)0.7Ca0.3MnO3 (grown on SrTiO3 or LaAlO3 substrates) upon the IR absorption spectra and the equatorial Kerr effect measured in the 1.5–3.8 eV range were studied. A giant drop in the temperature of maximum resistance of the film grown on SrTiO3 and disappearance of the metal-insulator transition in the film on LaAlO3, observed upon the isotope exchange, are accompanied by a decrease in the contribution of free charge carriers to the absorption spectra, by the appearance of bands due to localized states, and by a decrease in magnitude of the equatorial Kerr effects. Measurements of the Kerr effect and the temperature variation of the optical transmission show evidence of the presence of ferromagnetic metal regions in the 18O-isotope-substituted (La0.5Pr0.5)0.7Ca0.3MnO3/LaAlO3 film at low temperatures, with a general semiconductor character of the resistivity behavior in the entire temperature range studied. Changes observed in the absorption spectra are explained based on a model of the pseudo-Jahn-Teller polar centers and phase separation. The optical and magnetooptical data show evidence of a percolation nature of the giant isotope effect in manganites.

The optical spectra (reflection and absorption) of La0.85Sr0.15MnO3 (LSM) and La0.85Ba0.15MnO3 (LBM) single crystals are studied in the infrared range, where the interaction of charge carriers with light dominates. In paramagnetic state, the small lattice polarons dominate the optical properties of LBM single crystal but in the optical spectra of LSM crystal the polarons manifest themselves weaker. The activation energy of polaron hopping Ea is determined.

Optical absorption spectra, transverse Kerr effect, resistivity and magnetoresistance of polycrystalline films La1−xSrxCoO3 (x=0.15;0.25;0.35) are studied. The temperature dependences of optical and magneto-optical properties were found to have specific features which can be caused by changes in spin state of Co3+ ions. The results obtained support the phase separation scenario in doped cobaltates. Magnetic interaction between different phases is controlled by the number of Co3+ (intermediate-spin state, S=1) ions in the orbital ordered state.

The investigation of optical and magnetooptical properties of La x MnO 3 (0.83⩽ x ⩽1.10) films revealed the changes of spectra and of electronic structure caused by the deviation from the stoichiometry and by strain in the films. Transversal Kerr effect data, temperature dependencies of magnetotransmission and magnetoresistance give the evidence for existence of charge and magnetic phase separation. The experimental results are discussed within the theoretical model of effective medium.

The features observed in the frequency and temperature dependences of the optical spectra of doped manganites can be accounted for by assuming the latter to have inhomogeneous phase composition. The spectral response of the optical conductivity of the La1−xSrxMnO3 system was calculated in the effective-medium approximation over a broad range of x variation.

The charge and magnetic states of LaMnO 3 single crystal with electron doping by Ce (7%) have been studied and compared with undoped manganite and a Sr-doped compound. Extensive study including investigation of magnetic, transport properties, infrared optical absorption, electron-spin resonance, and neutron scattering have been performed. The substitution of La by donor impurity of Ce results in a partial compensation of holes induced by cation vacancies. Results are explained by charge segregation and “modulated” canted antiferromagnetic state.

The optical and magneto-optical properties of ferromagnetic La(1-x)Ba(x)MnO(3) single crystals with x=0.15, 0.20 and 0.25 are studied. The components of the permittivity tensor are obtained by spectral ellipsometry techniques and transverse Kerr effect measurements. The Kerr effect spectra depend substantially on the Ba content. The plasma frequency is estimated. In the paramagnetic semiconductor state, the small polarons contribute to conductivity in La(0.85)Ba(0.15)MnO(3), in La(0.75)Ba(0.25)MnO(3) no evidence for polarons is found even in the semiconductor state. For La(0.85)Ba(0.15)MnO(3) (T(C)=214 K), the metallic phase is estimated to occupy less than 1% of the total volume at T=190 K. It is shown that in La(0.75)Ba(0.25)MnO(3), the energy gap vanishes and the metal-semiconductor transition occurs somewhat below T(C) rather than at T=T(C).

The absorption spectra, temperature dependence of light transmission, and dc resistivity of ${\mathrm{La}}_{0.92}{\mathrm{Ca}}_{0.08}\mathrm{Mn}{\mathrm{O}}_{3}$ single crystal are investigated. The volume of the metallic phase in insulating matrix is evaluated by analyzing the temperature dependence of the light absorption and dc conductivity. Using the data published, we also calculate the metallic phase volume in ${\mathrm{La}}_{1\ensuremath{-}\mathrm{x}}{\mathrm{Sr}}_{\mathrm{x}}\mathrm{Mn}{\mathrm{O}}_{3}$, $x=0.07$ and 0.10. It is shown that in the lightly doped manganites, the metallic droplets lie in the ferromagnetically ordered regions, but only a small part of the ferromagnetic phase has metallic conductivity.

Optical absorption and transverse Kerr effect spectra, resistivity, and magnetoresistance of ${\mathrm{La}}_{1\ensuremath{-}x}{\mathrm{Sr}}_{x}{\mathrm{CoO}}_{3}(x=0.15,0.25,0.35)$ films have been studied. The temperature dependences of the optical and magneto-optical properties of the films exhibit features which can be attributed to the transition of the ${\mathrm{Co}}^{3+}$ ions from the low-spin state $(S=0)$ to the intermediate-spin state $(S=1)$ and to orbital ordering of the ${\mathrm{Co}}^{3+}$ ions in the latter state. The evolution of the properties influenced by doping with Sr is interpreted on the basis of the phase separation model.