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  • 1
    Electronic Resource
    Electronic Resource
    Effect of doping on the magnetic properties of the low-dimensional antiferromagnet CuO (1998)
    Springer
    Physics of the solid state 40 (1998), S. 1702-1705 
    Details
    ISSN: 1063-7834
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The effect of doping with Li+, Zn2+, Ni2+, and Ga3+ ions on the magnetic susceptibility of the low-dimensional antiferromagnet CuO (T N=230 K) has been studied within a broad temperature range of 77–600 K. The solubility of impurity ions in the CuO lattice is low, ⩽3%. Impurity ions, similar to intrinsic defects, distort antiferromagnetic coupling and can shift the long-and short-range magnetic-order regions toward lower T.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1134/1.1130638
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  • 2
    Electronic Resource
    Electronic Resource
    Polar-center phase nuclei in He+-irradiated CuO single crystals (1998)
    Springer
    Physics of the solid state 40 (1998), S. 383-388 
    Details
    ISSN: 1063-7834
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Irradiation of various single-crystal CuO faces [ac,bc,(110)] with 4.6-MeV He+ ions has been found to result in reduction of CuO to Cu2O and Cu on the irradiated and unirradiated sides, lifting of forbiddenness from optical transitions in the [CuO4]7− electron center in the 0.7–0.95-eV energy range, a change in dichroism near the bands corresponding to transitions in the hole centers, [CuO4]5−, and electron centers, [CuO4]7−, as well as in a resonant increase of absorption at 0.95–1.30 eV with an unusual polarization dependence. The results of He+ irradiation of CuO single crystals are discussed in terms of a model of the nucleation of the phase of polar (electron and hole) centers in copper-oxygen systems.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1134/1.1130329
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  • 3
    Electronic Resource
    Electronic Resource
    Role of surface phenomena in the magnetoresistivity of polycrystalline manganites La1−x CaxMnO3 (1998)
    Springer
    Physics of the solid state 40 (1998), S. 1706-1709 
    Details
    ISSN: 1063-7834
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The dc electrical resistivity and magnetoresistivity of polycrystalline manganites La1−x CaxMnO3 (x=0–0.3) are investigated as functions of the temperature, magnetic field and electric field, along with the microwave surface resistance. The investigations show that the dc electrical resistivity and magnetoresistivity are governed by the surface properties of the intergranular boundaries. The dc electrical resistivity is observed to decrease substantially (tenfold) for a comparatively small electric field (E⋟100 V/cm). Estimates are obtained for the internal electrical resistivity of the granules, the thickness of the contact layer (which depends on the temperature and the magnetic field), and the height of the potential barrier between the interfaces separating the surface layer and inner layer of a granule.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1134/1.1130639
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  • 4
    Electronic Resource
    Electronic Resource
    Paramagnetism in copper monoxide systems (1998)
    Springer
    Physics of the solid state 40 (1998), S. 268-271 
    Details
    ISSN: 1063-7834
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract This paper describes the problem of high-temperature superconductivity related to investigations of the magnetic susceptibility, electron paramagnetic resonance, and O Kα x-ray emission spectra of samples from the following systems based on copper monoxide: CuO-Cu, CuO-Cu2O and CuO-MgO. In all these systems, thermal processing results in a paramagnetism which is not observed in the individual components of these systems before they are processed. O Kα spectra of the interface of a Cu-single-crystal CuO film structure indicate the presence of not only Cu2+ but also Cu1+ ions in the layer of CuO in close contact with Cu. Possible reasons for the appearance of paramagnetism in these systems are discussed. It is proposed that a paramagnetic layer at the contact between the antiferromagnetic copper monoxide and the other copper-oxide phases or with copper could be the cause of the impurity metastability observed previously in the high-T c superconducting phase.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1134/1.1130290
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  • 5
    Electronic Resource
    Electronic Resource
    Influence of electron irradiation on the fundamental absorption edge of a copper monoxide CuO single crystal (1998)
    Springer
    Technical physics letters 24 (1998), S. 127-129 
    Details
    ISSN: 1090-6533
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract As a result of irradiation of a CuO single crystal with 5 MeV electrons, the fundamental absorption edge has an “Urbach” appearance and characteristic features appear near the edge. These changes are explained using a model of polar-center phase nuclei.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1134/1.1262021
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  • 6
    Electronic Resource
    Electronic Resource
    Heating of magnons by hot charge carriers and electrical properties of HgCr2Se4 (1997)
    Springer
    Physics of the solid state 39 (1997), S. 580-583 
    Details
    ISSN: 1063-7834
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Strong variations of the conductivity and the Hall coefficient as a function of the magnetic and electric field strengths are discovered in the ferromagnetic semiconductor HgCr2Se4. The nature of these phenomena is discussed in connection with its electronic structure and the strong interaction between the electric and magnetic subsystems in this magnetic semiconductor. The results can be interpreted within a model of ordinary semiconductors with consideration of the strong electron-magnon interaction specific to magnetic semiconductors, the heating of magnons by hot charge carriers, and the trapping of charge carriers (the formation of ferrons) due to the s-d exchange interaction.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1134/1.1129934
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  • 7
    Electronic Resource
    Electronic Resource
    Contribution of carriers to optical conductivity spectra of lanthanum manganites (1999)
    Springer
    Physics of the solid state 41 (1999), S. 426-432 
    Details
    ISSN: 1063-7834
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract To study the band structure and carriers in lanthanum manganites, measurements have been made of the reflectance spectra of single crystals and polycrystals in the 0.04–1.6-eV range and of the optical conductivity σ opt calculated by the Kramers-Kronig method as functions of the concentration and species of divalent ions in the paramagnetic (PM) and ferromagnetic (FM) regions. The optical gap for single-crystal La0.9Sr0.1MnO3 is ∼0.17 eV, and the polaronband energy is 0.12 eV. In the PM region, σ opt spectra do not indicate a band-carrier contribution, and conduction is dominated by polaron hopping and activation to the mobility edge. In the FM region, the variation in the σ opt and absorption spectra of La0.7Sr0.3MnO3 epitaxial films indicate the appearance of band carriers and a red shift of the absorption edge. The two band-carrier contributions, with weak and strong dependences on photon energy, are related to conduction in the antiferromagnetic matrix and the ferromagnetic regions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1134/1.1130796
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  • 8
    Electronic Resource
    Electronic Resource
    Angular dependences of the peak effect in Yba2Cu3Ox single crystals (1997)
    Springer
    Physics of the solid state 39 (1997), S. 369-373 
    Details
    ISSN: 1063-7834
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Angular dependences of the magnetization hysteresis loops have been studied at T=77 K on YBCO single crystals exhibiting the peak effect. The peak effect is shown to be related to the pinning of longitudinal vortices along the c axis at twin boundary-type ordered defects. The behavior of the peak effect at intermediate angles is explained by anisotropic magnetic field penetration into quasi-two-dimensional superconductors. In thin crystals with a dilute ordered-defect structure this can result in an enhanced peak effect due to formation of a vortex kink structure and to “internal” pinning of transverse vortex segments at Cu-O sheets.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1134/1.1130135
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  • 9
    Electronic Resource
    Electronic Resource
    Magnetic and electrical properties of Mg1−x CuxO solid solutions and magnetic shielding in Cu-Mg1−x CuxO structures (1999)
    Springer
    Physics of the solid state 41 (1999), S. 262-264 
    Details
    ISSN: 1063-7834
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Mg1−x CuxO solid solutions having an NaCl structure with 0⩽x⩽0.20 are synthesized and Cu-Mg1−x CuxO structures are prepared for superconductivity studies. The magnetic susceptibility χ, electron paramagnetic resonance (EPR), and electrical conductivity of the solid solutions are studied at temperatures of 5–550 K. It is shown that χ −1(T) obeys the Curie-Weiss law with a paramagnetic Curie temperature Θ close to zero and an effective magnetic moment μ eff=1.9 µ B, close to the 1.73 µ B of a Cu2+ ion with spin S=1/2. The width ΔH of the EPR line depends weakly on temperature and increases as x is raised. The volume narrowing of the EPR linewidth ΔH is used to estimate the exchange interaction parameter, 3×10−4 eV. The g-factor is close to 2 and is temperature independent. The electrical conductivity of Mg1−x CuxO at T=300 K is ≈10−11–10−12 Ω−1 cm−1 for x=0 and increases to 10−5–10−6 Ω−1 cm−1 for x=0.15–0.20. The conductivity is p-type. Magnetic shielding is observed in Cu-Mg1−x CuxO structures with x=0.15 and 0.20. The possible connection of this phenomenon with interference superconductivity in the contact layer of the structure is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1134/1.1130764
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  • 10
    Electronic Resource
    Electronic Resource
    An anomaly in the magnetic susceptibility of the Mg1−x CuxO solid solutions with 0.01≤x≤0.20 (2000)
    Springer
    Physics of the solid state 42 (2000), S. 719-721 
    Details
    ISSN: 1063-7834
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The problem of localized superconductivity has motivated the preparation of Mg1−x CuxO solid solutions with NaCl structure and 0.01≤x≤0.20, as well as a study of the magnetization and magnetic susceptibility χ in the 2–400 K temperature range and in magnetic fields of up to 5 T. The temperature dependence of χ is described for all compositions by the Curie-Weiss law, χ = C/(T − θ), where the constant C is close to the value calculated for each composition for μeff = 1.7–1.9µB, and θ is close to zero. For T 〈 30 K, χ(T) deviates for all compositions toward lower χ, which can be attributed to magnetic ordering of exchange-coupled clusters in the solid solution. At T∼320–330 K, an anomaly of a diamagnetic type, i.e., a decrease of χ by 6–30% of its paramagnetic value, has been observed for all compositions against the background of the generally paramagnetic χ(T). A discussion is presented of alternative reasons for this anomaly and of its possible connection with localized superconductivity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1134/1.1131278
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