Temperature dependence of magnetooptic effects in rare-earth magnetic semiconductor γ-Dy<Subscript>2</Subscript>S<Subscript>3</Subscript>

Temperature dependences of the Faraday effect (FE), which is linear in a magnetic field B; of the nonreciprocal linear birefringence (NB) associated with magnetic field-induced spatial dispersion; and of the Cotton-Mouton effect (CME), which is quadratic in a magnetic field B, have been studied in the transmission region of the γ-Dy₂S₃ cubic magnetic semiconductor (T _d symmetry class) at wavelength λ = 633 nm in the temperature range T = 25–294 K. As the temperature is lowered, the magnitudes of the FE and of the two main NB components, α₀₀₁ and α₀₁₁, increase in proportion to the magnetic susceptibility χ. This behavior implies that the magnitude of these effects is determined by the magnetic moment m of the Dy³⁺ ion induced by the magnetic field B. The CME component \(\beta _{001} (k||[1\bar 10],B||[001])\) grows in proportion to the magnetic susceptibility squared, χ²; i.e., β₀₀₁ ～ m². By contrast, the component \(\beta _{111} (k||[1\bar 10],B||[111]))\) exhibits a weaker temperature dependence, which indicates the manifestation of microscopic mechanisms in the CME component β₁₁₁ that differ from those for β₀₀₁.     

Special features of linear magnetic birefringence in an α-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>:Ga single crystal

Experimental investigations of the field dependence of the linear magnetic birefringence (LMB) in an α-Fe₂O₃:Ga single crystal are presented. It is established that during crystal magnetization in the basal plane near directions perpendicular to the С₂ axes in the region of magnetic field saturation, the LMB changes nonmonotonically. The observed special feature of the field LMB dependence is due to the reorganization of the magnetic α-Fe₂O₃:Ga structure during magnetization.     

Influence of Morphological Defects on Thermophysical Properties of γ-Gd<Subscript>2</Subscript>S<Subscript>3</Subscript>

The temperature dependences of the heat capacity (C _p ) and the thermal conductivity (κ) in the temperature range from 300 to 773 K of polycrystalline gadolinium sulfide samples (γ-GdS _y ) with the deviation of the composition from the integer stoichiometric were studied. It was found that the thermal conductivity of gadolinium sulfides decreases monotonically and reaches 0.74 W/(m K) at T = 773 K for the composition y = 1.479, which is much lower than for the known single-crystal samples. The influence of morphological defects (boundaries of crystallites and dislocations) on the intensity of scattering of phonons is studied. It has been established that ceramic samples of gadolinium sulphides have a large heat capacity and a lower thermal conductivity, in comparison with monocrystalline samples of the same composition.     

Photoinduced phenomena in amorphous As<Subscript>4</Subscript>S<Subscript>3</Subscript>Se<Subscript>3</Subscript>–Sn films

We investigate the kinetics of photodarkening and recording of holographic diffraction gratings in amorphous As₄S₃Se₃ thin-film structures doped with tin (Sn) in concentrations of 0–10 at %. It is established that an increase in the Sn concentration leads to a decrease in the photodarkening rate and degree. The photodarkening kinetics is approximated by a stretched exponential function. It is found that an increase in the Sn concentration leads to a decrease in the transmission (photodarkening) variation in the investigated As₄S₃Se₃–Sn films. It is determined that, in the recording of holographic diffraction gratings at a Sn concentration of 3–8 at %, the As₄S₃Se₃–Sn films exhibit the maximum sensitivity and diffraction efficiency of the recorded gratings. It is shown that the dependence of diffraction efficiency on the As₄S₃Se₃ film thickness has the maximum at a film thickness of 4 µm.     

Electrical switching in the MoO<Subscript>3</Subscript>–WO<Subscript>3</Subscript>–P<Subscript>2</Subscript>O<Subscript>5</Subscript> and MoO<Subscript>3</Subscript>–P<Subscript>2</Subscript>O<Subscript>5</Subscript> glasses

High field electrical switching on blown films of MoO₃(60%)–P₂O₅(40%), MoO₃(50%)–WO₃(10%)–P₂O₅(40%), and MoO₃(45%)–WO₃(15%)–P₂O₅(40%) having different thicknesses was studied and compared. Switching was observed using two terminal samples. S-type current–voltage characteristic (current-controlled negative resistance—CCNR) with memory was observed in molybdenum–phosphate glasses, but N-type characteristic (voltage-controlled negative resistance—VCNR) with threshold in tungsten–molybdenum–phosphate glasses was observed. The important observation was that with the addition of WO₃ to binary MoO₃–P₂O5 led to a change of I–V characteristic from CCNR with memory to VCNR with threshold. The measurements of density and molar volume showed linear relation between MoO₃ content and density which decreased with the increase of MoO₃ content. The samples’ thickness had no significant effect on threshold voltage. The attained results also indicated that the electrode material had no effect on switching property of devices. The switching behavior of the devices did not show any dependence on the polarity of the applied voltage. In terms of the effect of heat on the switching behavior of molybdenum–phosphate glasses, it was found that threshold voltage decreases with increasing of temperature. Finally, the switching phenomenon was explained by thermal (formation of crystalline filaments) and electronic models.     

Specific heat of the [NH<Subscript>2</Subscript>(CH<Subscript>3</Subscript>)<Subscript>2</Subscript>]<Subscript>2</Subscript>ZnCl<Subscript>4</Subscript> crystal in the temperature region 80–300 K

The specific heat of [NH₂(CH₃)₂]₂ZnCl₄ was measured calorimetrically in the temperature region 80–300 K. As the temperature T decreases, the C _p (T) dependence indicates a phase transition sequence, with the phase transition at T₆=151 K observed for the first time. The thermodynamic characteristics of the crystal were refined. The transformation occurring at T₂=298.3 K is shown to be an incommensurate-commensurate phase transition.     

Long-range magnetic order in copper nitrate monohydrate Cu(NO<Subscript>3</Subscript>)<Subscript>2</Subscript> · H<Subscript>2</Subscript>O

The magnetic phase diagram of copper nitrate monohydrate Cu(NO₃)₂ · H₂O and the basic parameters of its magnetic subsystem have been determined by measuring the thermodynamic properties of this compound. This compound becomes antiferromagnetically ordered at T _N = 3.6 K, undergoes the spin-flop and spin-flip transitions at H _C1 ～ 0.06 T and H _C2 ～ 1.1 T, respectively, at low temperatures. The magnetization of Cu(NO₃)₂ · H₂O at T _SR = 2.7 K exhibits an additional anomaly, which is likely attributed to the spin-reorientation transition.     

Magnetic and magnetoresistive properties of Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–Sr<Subscript>2</Subscript>FeMoO<Subscript>6–δ</Subscript>–Al<Subscript>2</Subscript>O<Subscript>3</Subscript> nanoheterostructures

A method has been developed for fabricating nanoporous matrices based on anodic aluminum oxide for the deposition of ferromagnetic nanoparticles in them. The modes of deposition of strontium ferromolybdate thin films prepared by the ion-plasma method have been worked out, and the magnetic and magnetoresistive properties, structure, and composition of the films have been investigated. It has been revealed that the microstructure and properties of the strontium ferromolybdate films deposited by ionplasma sputtering depend on the deposition rate and the temperature of the substrate. Based on the measurement of the electrical resistivity of nanoheterostructures in a magnetic field, it has been found that the magnetoresistance reaches 14% at T = 15 K and B = 8 T, which is due to the manifestation of tunneling magnetoresistance.     

Phase formation in the BaCO<Subscript>3</Subscript>–PbO–Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>–Nb<Subscript>2</Subscript>O<Subscript>5</Subscript> system

Features of the formation of lead-ferroniobate compounds in the xBaCO₃–(1 – x)PbO–Fe₂O₃–Nb₂O₅ system by solid-phase synthesis are investigated. For perovskite-type lead-ferroniobate solid solution, a single-phase concentration region is revealed at 1233 K. The crystalline structures of the synthesized compounds are refined using Rietveld analysis and the Pm3?m and R3m space groups. Ceramic samples of lead ferroniobate are studied by scanning electron microscopy.     

Penetration of a magnetic field into the YBa<Subscript>2</Subscript>Cu<Subscript>3</Subscript>O<Subscript>7−δ</Subscript> high-temperature superconductor: Magnetoresistance in weak magnetic fields

The penetration of a magnetic field into superconducting grains and weak links of YBa₂Cu₃O_7?δ ceramic high-temperature superconductors is investigated using measurements of the transverse and longitudinal magnetoresistances at T=77.3 K and 0≤H≤～500 Oe as a function of the transport current in the range ～0.01≤I/I _c ≤～0.99. The effects associated with the complete penetration of Josephson vortices into weak links of the high-temperature superconductor in magnetic fields H_c2J, the onset of penetration of Abrikosov vortices into superconducting grains in magnetic fields H_c1A, and the first-order transition from the Bragg glass phase to the vortex glass phase in fields H_BG-VG are revealed and interpreted. The I-H phase diagrams YBa₂Cu₃O_7?δ high-temperature superconductors are constructed for I ⊥ H and I ‖ H.     

Phase transition in the vortex structure of granular YBa<Subscript>2</Subscript>Cu<Subscript>3</Subscript>O<Subscript>7 − δ</Subscript> HTSCs in weak magnetic fields

This study aims at establishing the interrelation between the current-carrying capacity and peculiarities of magnetoresistance of granular YBa₂Cu₃O_{7 ? δ} HTSCs (T _c = 92.5 K). The transverse magnetoresistance of several batches of YBa₂Cu₃O_{7 ? δ} HTSC samples with noticeably different values of critical supercurrent density j _c is measured in magnetic fields H _ext up to H _ext ^max ≈ 500 Oe in a wide range of transport currents (5 mA ≤ I ≤ 1600 mA) at T = 77.4 K. Samples with relatively high values of j _c (H _ext = 0) ≥ 100 A/cm² do not exhibit any anomalies in their field dependences. Magnetoresistance jumps δρ_BG-VG/ρ_273K are observed for samples with low values of j _c ≥ 20 A/cm² in fields H _BG-VG ≈ 200–260 Oe. The width ΔH _BG-VG of the anomalous resistance region increases upon an increase in I. The magnetoresistance jumps decrease with increasing I in increasing field H _ext(0 → H _ext ^max ) and increase in decreasing field H _ext(H _ext ^max → 0). It is found that these peculiarities of the field dependences of magnetoresistance are associated with a first-order phase transition (in magnetic field) in the vortex structure of YBa₂Cu₃O_{7 ? δ} HTSCs of the Bragg glass-vortex glass type.     

Origin of the structural local transition in the molecular impurity ion MnO<Stack><Subscript>4</Subscript><Superscript>2−</Superscript></Stack> in the K<Subscript>3</Subscript>Na(CrO<Subscript>4</Subscript>)<Subscript>2</Subscript> ferroelastic

A new model is proposed for a local transition in a Jahn-Teller impurity center in a crystal with a ferroelastic (ferroelectric) phase transition. This model is based on direct interaction of the order parameter of the phase transition in the matrix with the Jahn-Teller impurity degrees of freedom. It is shown that, under these conditions, the order parameter field can induce lifting of degeneracy of the electronic states active in the Jahn-Teller effect, which is accompanied by a transition from the Jahn-Teller effect to the pseudo-Jahn-Teller effect with its subsequent suppression. As a result, a decrease in temperature gives rise to a structural local transition in the region of the low-symmetry ferroelastic (ferroelectric) matrix phase from the many-well local adiabatic to a single-well potential. The model proposed allows interpretation of experimental data obtained in an EPR study of the molecular impurity ion MnO ₄ ^2? in the K₃Na(CrO₄)₂ ferroelastic.     

Trapping of a magnetic flux in granular YBa<Subscript>2</Subscript>Cu<Subscript>3</Subscript>O<Subscript>7 − δ</Subscript> high-temperature superconductors under the action of an external magnetic field and transport current

Magnetic flux trapping (MFT) in granular YBa₂Cu₃O_{7 − δ} high-temperature superconductors (HTSCs) is studied. At T = 77.36 K, the dependence of the hysteresis of the transverse magnetoresistance on transport current I and the maximum value of external magnetic field H _ext is found in the measurement cycle 0 → H _ext^max → 0. The dependences of the parameters characterizing MFT, namely, residual magnetoresistance, field H _min at which the magnetoresistance is minimal, and the magnetoresistance at H _ext = H _min, on I and H _ext^maxare determined. MFT is found to occur in HTSC granules under the action of an external magnetic field exceeding the lower critical field of superconducting granules H _c1A, and the transport current only weakly affects the magnitude of MFT.     

Raleigh and Mandelshtam-Brillouin light scattering in chalcogenide glasses of the (As<Subscript>2</Subscript>S<Subscript>3</Subscript>)<Subscript>x</Subscript>I<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript> system

Raleigh and Mandelshtam-Brillouin light scattering has been investigated in chalcogenide glasses of the (As₂S₃)_xI_1−x system for x = 1.00−0.80. Longitudinal hypersound velocities, adiabatic elastooptical constants (p₁₂)_ad at frequencies of ∼15 GHz, and Landau-Placzek ratios R_LP are found and scattering losses are calculated. Significant iodine additives are shown to result in the appearance of different features in the behavior of concentration dependences of the investigated parameters. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 75, No. 6, pp. 814–818, November–December, 2008.     

Synthesis and characterization of CoFe<Subscript>2</Subscript>O<Subscript>4</Subscript>–Ba<Subscript>0.9</Subscript>Sr<Subscript>0.1</Subscript>TiO<Subscript>3</Subscript> magnetoelectric composites with dielectric and magnetic properties

Composite structures consisting of (001)-oriented SrTiO₃ (STO)/La_0.7Sr_0.3MnO₃ (LSMO) films of 30 nm thickness, grown on an (001) Pb(Mg_1/3Nb_2/3)TiO₃– 28 mol.% PbTiO₃ piezoelectric relaxor-ferroelectric single-crystalline wafer were investigated by means of Wide-Angle X-ray Diffraction (WAXRD) in situ under influence of a d.c. electric field with strength E up to ±18 kV/cm. The WAXRD measurements of the films and substrate reflection profiles resulted in a determination of the strain s in the films and the substrate separately. The strained state of the STO/LSMO films is effectively controlled by a huge converse piezoelectric effect of the PMN-PT substrate. The coefficients of coupling between electric-field-induced out-of-plane strain in the films and in the substrate for the composite system STO/LSMO/PMN-PT are obtained.     

Influence of Matrix Nature on the Structural Characteristics of In<Subscript>2</Subscript>O<Subscript>3</Subscript>–CeO<Subscript>2</Subscript> and SnO<Subscript>2</Subscript>–CeO<Subscript>2</Subscript> Composites Fabricated by the Impregnation Method

The structural characteristics, valence states, and distribution of cerium ions between the components in In₂O₃–CeO₂ and SnO₂–CeO₂ nanocomposites fabricated using the impregnation method were studied. X-ray photoelectron spectroscopy (XPS) and energy-dispersive X-ray spectroscopy (EDX) were used to show that, during impregnation, cerium ions are not included into In₂O₃ crystals and are disposed only on their surface in the form of nano-sized crystallites or amorphous clusters. On the other side, under the contact of CeO₂ clusters with a surface of SnO₂ matrix crystals, cerium ions penetrate into the surface layer of these crystals. In contrast to an In₂O₃–CeO₂ system, where the addition of CeO₂ does not affect the conduction activation energy, where cerium oxide is added to SnO₂, the observed increase in the resistance of a SnO₂–CeO₂ composite is accompanied by a sufficient increase in activation energy. These data and the XPS spectra confirm the modification of the surface layers of conductive SnO₂ crystals as, a result of the penetration of cerium ions into these layers.