Electron spin resonance and luminescence in Ga2−xEuxS3 single crystals

In present work electron spin resonance (ESR) and luminescence have been studied in Ga_2−xEu_xS₃ single crystals. The ESR and photoluminescence (PL) spectra of Ga_2−xEu_xS₃ were observed and the intensity of these spectra has increased linearly with the Eu concentrations in the samples. At the low temperature of 3.8 K in Ga_2−xEu_xS₃ single crystals, when the magnetic field has been applied as the perpendicular to the direction of [110], the hyperfine structure of ESR spectra has been observed. The exchange interaction of Eu²⁺ atoms in Ga_2−xEu_xS₃ single crystals have been determined as, g=4.2. The PL spectrum of pure Ga₂S₃ single crystals was recorded at 4.2 K and consisted of a narrow high-energy band at 2.53–2.38 eV and a low-energy band at 2.14–1.59 eV. Ga_2−xEu_xS₃ resulted in complete quenching of the impurity luminescence bands gave rise to a green europium band (2.38–2.14 eV) in the luminescence spectrum. Crystals of Ga_2−xEu_xS₃ emitted bright green electroluminescence (EL) spectrum when they excited with static and alternating electric fields at 77 K. We have also determined the field and frequency dependences of the EL.     

Electron paramagnetic resonance study of S− and S− 3

Abstract

Two new sulphur are reported in monocristalline rubidiumchloride doped with rubidium and sulphur, and irradiated with X-rays at room temperature. By an extensive comparison with other experimental data on chalcogen centres in alkali halides an interstitial RbCl:S^? and a substitutional RbCl:S^? ₃ model is proposed for these paramagnetic defects. Theoretical calculations confirm the S^? ion model for the former.     

Specific heat of Na1−x V2O5 single crystals

Temperature dependences of the specific heat C and the magnetic susceptibility χ of Na_1?x V₂O₅ single crystals (x=0, 0.01, 0.02, 0.03, and 0.04) are studied. In NaV₂O₅, the transition to the spin-gap state (T _c =34 K) is accompanied by a sharp decrease in χ, while C exhibits a λ-shaped anomaly. At low temperatures, the specific heat of NaV₂O₅ is approximated by the sum of phonon ～T ³ and magnon ～exp(?Δ/T) contributions, which makes it possible to estimate the Debye temperature Θ_D=336 K and the gap in the magnetic excitation spectrum Δ=112 K. With the departure from stoichiometry, the anomalies observed in the behavior of χ and C are spread and shifted to lower temperatures. The low-temperature specific heat of nonstoichiometric samples is determined by the sum of phonon and magnon components and the contribution due to the presence of defects. The values of magnetic entropy characterizing the phase transitions in Na_1?x V₂O₅ are calculated.     

Electrical properties and electronic structure of Cu1−xZnxInSe2 and Cu1−xZnxInS2 single crystals

Temperature dependence of the electrical conductivity of CuInS₂–ZnIn₂S₄ and CuInSe₂–ZnIn₂Se₄ solid solutions possessing n-type conductivity has been studied. It has been established that when the temperature decreases down to ~100 to 27 K, the hopping mechanism of electrical conductivity with a variable jumping length between localized states positioned in a narrow energy band near the Fermi level becomes dominant. The main parameters of the hopping conductivity have been determined. At higher temperatures (150–300 K), in the CuInSe₂–ZnIn₂Se₄ single crystals containing 15 and 20 mol% ZnIn₂Se₄ the thermally activated conductivity with activation energy of 0.018 and 0.04 eV, respectively, is detected. Among the CuInSe₂–ZnIn₂Se₄ single crystals, samples with 5 and 10 mol% ZnIn₂Se₄ were found to be close to degenerate semiconductors. Temperature dependences of the electrical conductivity of CuInS₂–ZnIn₂S₄ single crystals are described by a more complicated function that may indicate a competition of several conduction mechanisms in these compounds. For the CuInS₂–ZnIn₂S₄ solid solutions, X-ray photoelectron core-level and valence-band spectra have been measured for both pristine and Ar⁺ ion-bombarded surfaces. Our results indicate that the Cu_1−xZn_xInS₂ single-crystal surfaces are sensitive to Ar⁺ ion-bombardment. Additionally, for the Cu_1−xZn_xInS₂ crystal with the highest ZnIn₂S₄ content, namely 12 mol% ZnIn₂S₄, the X-ray emission bands representing the energy distribution of the Cu 3d, Zn 3d and S 3p states have been measured and compared on a common energy scale with the X-ray photoelectron valence-band spectrum.     

Characterization and magnetic properties of electrospun Co1−x Zn x Fe2O4 nanofibers

By the electrospinning and calcination techniques, we have prepared uniform nanofibers of Co_1−x Zn _x Fe₂O₄ (0.0≤x≤0.5) ferrites with diameters of 110–130 nm. The Co_1−x Zn _x Fe₂O₄ nanofibers are single-phase spinels and the lattice constant with Zn content deviates from the Vegard’s law for these Co_1−x Zn _x Fe₂O₄ nanofibers. The Co_1−x Zn _x Fe₂O₄ nanocrystal grains by which are built nanofibers increase with calcination temperature. Variations of coercivity and saturation magnetization with calcination temperature can be explained in terms of the grain-size (D) effect. The coercivity (H _c) of Co_0.5Zn_0.5Fe₂O₄ nanofibers varies as D ^0.65 and basically follows the predicted D ^2/3 dependence based on the random anisotropy model in a D range below the single-domain size around 40 nm. The saturation magnetization of Co_1−x Zn _x Fe₂O₄ nanofibers initially increases with increasing Zn content, reaches a maximum value at x=0.3 and then decreases with further increase of Zn content, while the coercivity exhibits a continuous reduction with the increase of Zn content.     

Heat capacity of La1−x SrxMnO3 single crystals in different magnetic states

The heat capacity of three single-crystal samples of La_1?x Sr_xMnO₃ (x=0, 0.2, and 0.3) is measured in the temperature range 4–400 K. It is found that the heat capacity undergoes abrupt changes due to the transitions from the antiferromagnetic phase to the paramagnetic phase (x=0) and from the ferromagnetic phase to the paramagnetic phase (x=0.2 and 0.3). The phonon contribution to the heat capacity and the Debye characteristic temperatures for the La_0.7Sr_0.3MnO₃ sample are determined over a wide range of temperatures. The electronic density of states at the Fermi level is evaluated. It is demonstrated that an increase in the strontium concentration x brings about an increase in the electronic density of states at the Fermi level. The contributions of spin waves to the heat capacity and the entropy are estimated under the assumption that the phonon spectrum remains unchanged upon doping with Sr.     

Magnetic susceptibility studies of Zn1−xFexSe and Zn1−xFexS

The magnetic susceptibility of diluted magnetic semiconductors Zn_1−xFe_xSe and Zn_1−xFe_xS has been calculated within a crystal field model and by applying the extended nearest-neighbour pair approximation. The results are compared with available experimental data. It appears that a good agreement between theory and experiment is obtained for Zn_1−xFe_xSe taking the long-range exchange comprising several nearer interionic distances, whereas in Zn_1−xFe_xS the exchange interaction with nearest-neighbours alone gives a better solution.     

On the magnetic susceptibility of Pd1−x Ag x in the range 0.5≦x≦1

The weak variation of the magnetic bulk susceptibility of Pd_1–x Ag _x with temperature T and silver mole fractionx within 0.5x1 has been investigated in the range 5KT400K. Experimental evidence can be given for an intersection point of the susceptibility isotherms (T=const,x) atx=0.55. The observed dependence of on T andx is interpreted by means of a semiphenomenological alloy susceptibility function (T,x).     

Heat capacity and thermal conductivity of Fe x Mn1 − x S single crystals

This paper reports on the results of investigations of the thermal properties and thermal conductivity of single crystals of homogeneous solid solutions Fe _x Mn_{1 ? x} S with a cubic NaCl structure, which have been prepared by the cation substitution for divalent manganese ions in manganese monosulfide. It has been revealed that the heat capacity and thermal conductivity exhibit anomalies in the range of the magnetic transition. The cation substitution is accompanied by an increase in the phase transition temperature.     

Electron spin resonance measurements on single crystals of the organic superconductor κ-(BEDT-TTF)2I3

Angularly and temperature-dependent electron spin resonance (ESR) measurements on single crystals of the organic superconductor κ-(bis(ethylenedithiolo)-tetrathiafulvalene)₂I₃ are reported. The results on the anisotropy of theg-value, the temperature dependence of the susceptibility as well as of the ESR linewidth are discussed.     

Investigation of the effect of annealing on the magnetic properties of Sn1−xEuxTe single crystals

A study of the effect of annealing on the magnetic properties of single crystals Sn_1−xEu_xTe is reported. The width of the electron paramagnetic resonance line of the crystal is found to decrease upon annealing but its g-value of 1.991 is nearly unaffected. Magnetization results indicate that the pair exchange interaction is weakly antiferromagnetic with a value of −0.67 K for the non-annealed sample and −0.29 K after annealed sample. Susceptibility measurements performed as a function of temperature also indicate the presence of EuTe clusters in the as-grown Sn_1−xEu_xTe crystals. Therefore it was deduced that the Eu²⁺ ions tend to form clusters, particularly pairs, in the as-grown crystal and these clusters disappear after annealing, as the Eu²⁺ ions occupy isolated sites in the SnTe host lattice.     

Anisotropy of normal resistivity in oxygen-deficient YBa2Cu3O7−x single crystals

Temperature dependences of the resistivity tensor components ρ_ab and ρ_c were measured for YBa₂Cu₃O_7?x single crystals with different oxygen contents. The resistivity anisotropy ρ_c/ρ_ab was found to grow exponentially with decreasing temperature. The results are compared with the predictions of different models describing transverse transport in the normal state of cuprate high-T _c superconductors.     

Electron spin resonance and cation distribution studies of the Co0.6Zn0.4MnxFe2−xO4 ferrite system

The ESR spectra of the ferrite system Co_0.6Zn_0.4Mn_xFe_2−xO₄ (x=0, 0.1, 0.2, 0.3, 0.4 and 0.5) were obtained at room temperature. The experimental values of the magnetic moment (μ_exp) were estimated from the ESR spectra and the cation distribution was consequently established from the values of μ_exp. The systematic decrease in ESR line width observed in our present study was attributed to the decrease of Fe²⁺ concentration with increasing Mn content. The resonance field decreases and reaches a minimum at high values of Mn content whereas the magnetic moment reaches a maximum at these values. The IR spectra were recorded in the range 200–1200 cm⁻¹. The bands at 569 (ν₁) and 389 cm⁻¹ were assigned to the tetrahedral and octahedral complexes, respectively. The band at 441 cm⁻¹ is due to the Mn–O bond vibration. The theoretical lattice parameter was calculated and was found to be larger than the experimental one a_exp due to the presence of Mn⁴⁺ ions.     

Resistivity and magnetic susceptibility of superconducting and non-superconducting ErBa2Cu3O7−y

The oxide ErBa₂Cu₃O_7−y has been obtained in the orthorhombic and the tetragonal forms by suitable heat treatments. The orthorhombic form is metallic and superconducting with T_c=88 K while the tetragonal form has high resistance and is non-superconducting. Magnetic studies on both types of compounds reveal that the rare earth ion moment is very close to its free ion value independent of the structure. In the tetragonal compound, deviations in the susceptibility from the Curie-Weiss behavior are noted at low temperatures which may be due to the effect of crystalline electric fields.     

Thermal conductivity of single crystals of the Ca1 − x Y x F2 + x solid solution

The thermal conductivity of single crystals of the solid solution of yttrium fluoride in calcium fluoride Ca_{1 ? x} Y _x F_{2 + x} with the fluorite structure (x ≤ 0.20) and the Ca_0.27Y_0.73F_2.73 phase with the tisonite structure has been studied by the absolute steady-state longitudinal heat flow method in the temperature range 50–300 K. It has been established that the thermal conductivity drops sharply with increasing yttrium trifluoride concentration, especially in the low-temperature region.     

Electron spin resonance and structure of the ionic radical, ·PO3 =

It is shown that the ionic radical, ·PO₃ ⁼, is formed by the action of γ-rays on disodium ortho-phosphite pentahydrate. The hyperfine coupling to the ³¹P nucleus has principal values of 1967, 1514 and 1513 Mc/s and is consistent with a pyramidal ion having OPO angles of 110°.     

On the magnetic susceptibility of the liquid Pd1−x Si x alloy system at 1825 K

The isothermal magnetic susceptibility (x) of the completely miscible liquid Pd_1–x Si _x alloy system shows a rapid monotonous decrease withx from strong paramagnetism to weaklyx-dependent diamagnetism. The measured susceptibility isotherm at 1825 K is analysed within 0x1 by using a semiphenomenological method of decomposing the magnetic susceptibility into its constituent parts. Because of the empirical similarity between liquid and glassy metals this interpretation also provides assertions about the magnetism of glassy Pd_1–x Si _x aroundx=0.2.     

Unique features of the magnetic susceptibility of Hg1−xMnxTe1−ySey

The magnetic susceptibility of the new semimagnetic solid solutions Hg_1–xMn_xTe_1–ySe_y (0Mn = f(T) are caused by the presence within the specimen of Mn-Te-Mn-Te, Mn-Se-Mn-Se, and Mn-Te-Mn-Se type clusters, in which indirect exchange action of an antiferromagnetic character occurs among the Mn atoms by means of the Te or Se atoms.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 60–62, April, 1991.     

Effect of pressure on electrical properties of SnS x Se1−x single crystals

The single crystals of tin monosulphoselenides in the form of a series SnS _x Se_1?x (where x?=?0, 0.25, 0.50,0.75 and 1) have been grown using the direct vapor transport technique (DVT). The analysis of the X-ray diffraction patterns reveals that all crystals belong to the orthorhombic crystal structure. Hall effect measurements were carried out on grown crystals at room temperature. The optical absorption measurements at room temperature have been carried out for all crystals. The values of the band gap were determined at atmospheric pressure and also calculated at high-pressure. Simultaneous thermoelectric power (TEP) and a.c. resistance measurements up to 8?GPa were carried out. The results of the effect of high-pressure on the electrical resistance of the grown crystals are reported in this paper.