E. V. Mostovshchikova

Anomalies in the optical properties of nanocrystalline copper oxides CuO and Cu2O near the fundamental absorption edge

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.

Nanocrystalline copper oxide for selective solar energy absorbers

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.

The influence of magnetic and electronic inhomogeneities on magnetotransmission and magnetoresistance of La0.67Sr0.33MnO3 films

The optical (absorption of light and magnetotransmission of IR radiation), magnetic, and transport properties of the epitaxial La0.67Sr0.33MnO3 films of different thickness grown by laser ablation on the (100) SrTiO3 and LaAlO3 substrates were investigated. The effect of magnetotransmission reaches 6% at the temperature of 350K while magnetoresistance reaches 7.6% at 354K in a magnetic field of 8kOe. The factors, which influence the values of magnetotransmission and magnetoresistance of manganite films, are discussed.

Effect of isovalent doping of manganite (La1−xPrx)0.7Ca0.3MnO3 films (0≤x≤1) on their optical, magnetooptical, and transport properties near the metal-insulator transition

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.

IR radiation modulator based on the effect of magnetotransmission in lanthanum manganite operating near room temperature

A prototype of the IR radiation modulator operating at T=303 K, using the giant magnetotransmission effect in a La0.82Na0.18MnO3+δ lanthanum manganite film, has been constructed and the optical characteristics of the setup have been measured. In a wavelength range from 1.4 to 11 μm, the IR modulation depth varies from 3.5 to 6.5%. The possibilities of increasing the modulation depth are considered.

Optical and magneto-optical properties of ferromagnetic La1 ? xBaxMnO3 single crystals

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).

Spin states and phase separation in La 1 − x Sr x CoO 3 ( x = 0.15 , 0.25 , 0.35 ) films: Optical, magneto-optical, and magnetotransport studies

Optical absorption and transverse Kerr effect spectra, resistivity, and magnetoresistance of

The evolution of the optical spectra of LaMnO3 under light n-and p-type doping and the separation of phases

{\mathrm{La}}_{1\ensuremath{-}x}{\mathrm{Sr}}_{x}{\mathrm{CoO}}_{3}(x=0.15,0.25,0.35)

Electronic structure and phase separation in LaxMnO3 films (0.83≤x≤1.10): Optical and magnetooptical data

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

Nanoscale phase separation in La0.7Ca0.3MnO3 films: evidence for texture-driven optical anisotropy

{\mathrm{Co}}^{3+}