Magnetization-odd nonreciprocal reflection of light from the magnetoelectric—ferromagnet LiFe5O8

Circular dichroism, which changes sign under magnetization reversal and exhibits a 120° periodicity, is observed in the reflection of light from the (111) plane of a noncentrosymmetric LiFe₅O₈ crystal in the transverse geometry k⊥M, where the linear Kerr effect is forbidden. It is shown that this phenomenon is due to the manifestation of optical magnetoelectric susceptibility and a Kerr effect of third order in the magnetization. The spectral dependences of the circular dichroism in the range 1.4–3.1 eV show that this phenomenon is of a resonance character. Pis’ma Zh. éksp. Teor. Fiz. 65, No. 1, 65–70 (10 January 1997)     

Dufour effect in superionic copper selenide

The Dufour effect has been observed in the superionic conductor copper selenide, Cu_2−x Se. This effect is the opposite of the Soret thermal diffusion effect which was previously only observed in gaseous and liquid systems. Fiz. Tverd. Tela (St. Petersburg) 40, 242–244 (February 1998)     

Detection of (<Emphasis Type="Italic">C</Emphasis> + <Emphasis Type="Italic">A</Emphasis>)-type dislocation self-blocking in magnesium

The self-blocking effect predicted theoretically and then observed in intermetallides is established for a pure metal, namely, for magnesium. This effect can be observed only for magnesium single crystals whose axis is parallel to the c axis and whose yield stress behavior σ _y (T) has a temperature anomaly. For such single crystals, the self-blocking of the (c + a)-type edge dislocations is established during pyramidal slip of type II. The self-blocking is proved by dislocation extension along the preferred direction without external stress. In this case, the á 1[`1]00 ñ \left\langle {1\bar{1}00} \right\rangle directions appear preferred. TEM images of (c + a) dislocations extended along the preferred directions are presented. It is demonstrated that two effects – temperature anomaly of σ _y (T) and dislocation self-blocking – have the common nature: a two-valley potential relief of the dislocation. A model of two-valley relief of the (c + a) dislocations in Mg is proposed.     

The invar effect and phase transitions in Cs2ZnI4 crystals

An in situ x-ray diffraction study of Cs₂ZnI₄ crystals performed in the 4.2–300 K temperature range is reported. The lattice parameter measurements have revealed three anomalies corresponding to phase transitions. The thermal expansion coefficient along the c axis was found to vanish in the region of incommensurate and commensurate modulated phases, 120–96 K (the invar effect). A possible crystallographic model relating modulated atomic displacements to the invar effect is discussed. Fiz. Tverd. Tela (St. Petersburg) 41, 137–142 (January 1999)     

Acoustic emission in the chalcogenide glass Ge0.18As0.28Se0.54

The effect of structural relaxations, which are caused by a temperature change as well as induced by external ultrasonic loading, on the velocity of elastic waves and on the acoustic noise spectrum in the chalcogenide glass Ge_0.18As_0.28Se_0.54 is investigated. The acoustically stimulated “softening” of the glass, observed for the first time, and acoustic emission signals, also observed for the first time, suggest that this method can be used to study structural changes in glass-like materials. Fiz. Tverd. Tela (St. Petersburg) 40, 1623–1626 (September 1998)     

Effect of free electron-hole pairs on the saturation of excitonic absorption in GaAs/AlGaAs quantum wells

The pump-probe experimental method is used to investigate the effect of photoexcited carriers on the dynamics of the exciton absorption spectra of GaAs / Al_xGa_1–x As-multilayer quantum wells. Use of the method of moment analysis for processing the results makes it possible to identify the simultaneous contribution of changes in oscillator strength and width of the exciton lines in the saturation of exciton absorption. It was found that the oscillator strength recovers its initial value in the course of the first 100–130 ps, whereas broadening and energy-shift of the exciton lines is observed for 700–800 ps. These are the first experimental measurements of the excitation densities at which the oscillator strength of the excitonic state saturates when the latter is perturbed only by free-electron-hole pairs, and when it is perturbed only by other excitons. Fiz. Tverd. Tela (St. Petersburg) 40, 1130–1133 (June 1998)     

Structural and magnetic phase transitions in La0.9Sr0.1MnO3

A study is made of phase transitions in doped La_0.9Sr_0.1MnO₃ compounds using combined x-ray, electrical, and magnetic measurements. Structural phase transitions are observed accompanied by a change in the cell volume at temperatures of 100–110 K and 300–340 K. These structural changes are found to be related to different contributions of the rhombic Jahn-Teller Q ₂ mode to the formation of the crystal lattice. The structural transition at 100–110 K is accompanied by distinctive magnetic and electrical properties. The data are analyzed in detail. Fiz. Tverd. Tela (St. Petersburg) 41, 1064–1069 (June 1999)     

Radio-frequency absorption study of the parameters of high-T c materials irradiated with fast reactor neutrons

The magnetic properties of YBa₂Cu₃O_7−x ceramics of various densities and Bi₂Sr₂CaCu₂O₈ quasicrystals irradiated with neutrons at fluences of 10¹⁶–10¹⁹ cm⁻² are investigated by a radio-frequency method (in the frequency range f=100–150 MHz). The electromagnetic absorption is used to estimate the parameters of a Josephson medium: the lower critical field, the critical current density, the grain size and intergranular distances, and the penetration depth of the magnetic field in the sample. The hysteresis of electromagnetic absorption in the indicated superconductors is investigated; the hysteresis effect can be used to obtain data on flux pinning processes and flux creep dynamics. It is shown that an increase in the critical current density is observed as a result of the injection of radiation-induced pinning centers. Fiz. Tverd. Tela (St. Petersburg) 39, 28–34 (January 1997)     

Excitons in ZnP2 crystals in the electric field of a Schottky barrier

A study is made of the effect of electric fields on the exciton states of β-ZnP₂ crystals (T=77 K) in structures with Schottky barriers formed by depositing semitransparent electrically-conducting InSnO₂ films on the crystal surface. The observed changes in the exciton optical reflection spectra when an electrical potential is applied to a barrier are explained by the shift and broadening of the exciton level caused by the Stark effect. The experimental data are compared with calculations based on a theory of exciton optical reflection from planar spatially nonuniform structures. Fiz. Tverd. Tela (St. Petersburg) 40, 884–886 (May 1998)     

Isotope effect in the vibrational spectra of water measured in experiments with a scanning tunneling microscope

The vibrational frequencies of adsorbed H₂O and D₂O molecules are measured under high-vacuum conditions by in-cavity scanning tunneling spectroscopy. An isotope effect is observed. Pis’ma Zh. éksp. Teor. Fiz. 66, No. 1, 37–39 (10 July 1997)     

Low-temperature (T<180 K) relaxation processes and possible “electronic phase separation” in RBa2Cu3O6+x (R=Y,Tm, Lu) single crystals

Low-temperature (120–180 K) relaxational effects are observed in oxygen-deficient RBa₂Cu₃O_6+x (R=Y, Tm, Lu) single crystals. Isothermal holding of the crystals after rapid cooling increases their resistance. The characteristic times and the activation energy of the relaxation process, E _a ≈0.46 eV, are determined. The possible relation between the observed effects and the appearance of “electronic phase separation” is discussed. Pis’ma Zh. éksp. Teor. Fiz. 63, No. 10, 788–791 (25 May 1996)     

Effect of a constant magnetic field on the photoconductivity of single-crystal C60

Magnetic fields with induction B<1 T are found to affect the photocurrent in single-crystal C₆₀. This effect does not reduce to the Hall effect. The effect of the field on the multiplicity of short-lived pairs consisting of mobile carriers and their traps is proposed as a possible explanation for the observed phenomenon. Fiz. Tverd. Tela (St. Petersburg) 41, 2097–2099 (November 1999)     

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.     

Size effect in isometric PbTiO3 crystals

The phase transitions Pm3m⇄P4mm and domain-structure formation in 5–500 μm isometric PbTiO₃ crystals were investigated. The phase transition is characterized by a high rate and by the formation of a single flat interphase boundary {023}. A size effect was observed: In crystals smaller than a critical size (about 20 μm), formation of 90° domains stops and, in agreement with a phenomenological theory, the temperature hysteresis of the phase transition doubles. Fiz. Tverd. Tela (St. Petersburg) 40, 1546–1547 (August 1998)     

Influence of magnetic scattering centers in the insulator component of the composite HTSC+Cu1−x NixO on its resistive properties

We present results of an experimental study of the effect of magnetic scattering centers (nickel) in the insulator component (cuprous oxide) of the composite HTSC+Cu_1−x Ni_xO on its transport properties. A suppression of the superconducting properties of this system is observed to take place with increasing nickel content. The results are analyzed within the framework of the model of strong electron correlations. Fiz. Tverd. Tela (St. Petersburg) 40, 1599–1603 (September 1998)     

Spin-lattice relaxation and Knight shift on protons in the hydrogen-doped superconducting system H0.2La1.8Sr0.2CuO4

Measurements of the spin-lattice relaxation rate and Knight shift on protons in hydrogen-doped superconducting H_0.2La_1.8Sr_0.2CuO₄ samples are performed in the temperature range 4.2–300 K. An anomalous behavior of the spin-lattice relaxation rate is observed at low temperatures T∼20 K. A model is constructed that explains the appearance of carrier-depleted regions in the bulk of the semiconductor on the basis of the formation of a charged defect (proton). Pis’ma Zh. éksp. Teor. Fiz. 63, No. 7, 533–538 (10 April 1996)     

Fluorescence of N,N-di(2-carboxyethyl)-<Emphasis Type="Italic">p</Emphasis>-anisidine in solution and crystalline states

The fluorescence properties of N,N-di(2-carboxyethyl)-p-anisidine (I) in solvents of various nature and in the crystalline state have been studied at room temperature (273 K) and at the boiling point of liquid nitrogen (77 K). Fluorescence in aqueous solutions of I with protonated (λ _ex /λ _fl ^max = 225/290 nm) and unprotonated (λ _ex /λ _fl ^max = 270/380 nm) amino nitrogen has been detected. On going from aqueous solutions to nonaqueous, the fluorescence band of unprotonated I experiences a blue shift and its intensity rises. The fluorescence intensity of the band in aprotic polar solvents is higher than that in protic solvents. A linear dependence of the fluorescence intensity of deprotonated I on Cu(II) concentration (ranging from 1.0 to 5.0 mg/dm³) in aqueous solution has been found. The fluorescence intensity of I in aqueous solutions at 77 K and pH 1–6 has been shown to increase in the presence of Zn(II) (1–170 mg/dm³) and Cd(II) (2–330 mg/dm³) although a similar dependence is not observed at 293 K.     

Hall effect in microscopically inhomogeneous magnetic alloys

A theory of the generalized conductivity for the normal component of the Hall effect is developed. It is shown that the normal Hall effect coefficient R ₀ of microscopically inhomogeneous magnetic alloys GdZn_xCu_1−x , which at low temperatures consist of ferro-, antiferro-, and paramagnetic phases, can be described satisfactorily on the basis of an effective-medium theory. The experimentally observed relationship between the coefficient R ₀(x) and the resistivity ρ(x) is obtained. Fiz. Tverd. Tela (St. Petersburg) 41, 98–102 (January 1999)     

Low-temperature electronic and magnetic transitions in the antiferromagnetic semiconductor Cr0.5Mn0.5S

Experimental-theoretical studies were carried out of the electrical and magnetic properties of the antiferromagnetic semiconductor Cr_0.5Mn_0.5S in the temperature range 4.2–300 K. A magnetic antiferromagnetic-ferrimagnetic phase transition was observed along with a semimetalsemiconductor electronic transition. Monte Carlo calculations indicate that the changes in the type of magnetic ordering and conductivity are due to the cooperative Jahn-Teller effect caused by the Cr₂₊ ions. Fiz. Tverd. Tela (St. Petersburg) 41, 1660–1664 (September 1999)     

Anomalous millimeter-wave absorption in the superconducting phase of La2−x SrxCuO4

Direct measurements of the complex conductivity spectra of thin-film La_2−2x Sr_xCuO₄ are made at frequencies of 5–40 cm⁻¹. Narrow, intense Drude-type excitation is observed in the superconducting phase. Pis’ma Zh. éksp. Teor. Fiz. 68, No. 5, 406–409 (10 September 1998)