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We report a comprehensive study on hysteresis behaviour of current-voltage characteristic and impedance spectroscopy of granular semicrystalline poly(vinyl alcohol) (PVA) film. The charge carrier conduction mechanism and charge traps of granular PVA film by measuring and analyzing the temperature dependent current-voltage characteristic indicate a bi-stable electronic state in the film. A sharp transformation of charge carrier conduction mechanism from Poole-Frenkel emission to space charge limited current mechanism has been observed. An anomalous oscillatory behaviour of current has been observed due to electric pulse effect on the molecular chain of the polymer. Effect of microstructure on charge transport mechanism has been investigated from impedance spectroscopy analysis. An equivalent circuit model has been proposed to explain the result.

The frequency-dependent properties of Mn-doped (3–5 at.%) aligned zinc oxide (Mn–ZnO) nanorods, synthesized by hybrid wet chemical route onto glass substrates, were investigated by bias-dependent impedance spectroscopy. No peak of Mn cluster/secondary phases was detected in the X-ray diffraction traces of the samples. XPS studies show the presence of oxygen vacancies in Mn–ZnO nanorods and Mn in Mn2+ and Mn4+ charge states. Although X-ray diffraction/X-ray photoelectron spectroscopy does not give any indication of the presence of metal clusters in the samples, bias-dependent impedance spectroscopy demonstrates significant sensitivity to the formation of Mn clusters in Mn–ZnO nanorods.

We report enhancement of magnetization below the antiferromagnetic ordering temperature T N in nanoparticles of two antiferromagnets, viz CoRh2O4 and Cr2O3. The enhancement of magnetization below T N is systematic, being larger for sample with smaller particle size. Scaling analysis showed that such enhancement of magnetization in CoRh2O4 nanoparticles is due to the superparamagnetic type contribution of surface (shell) spins. The present work shows that similar analysis can also be applied in Cr2O3 nanoparticles.

The magnetization of the D 0 3 type Heusler alloy (Fe 1− x V x ) 3 Al with compositions 0.18≤ x ≤0.33, has been measured at temperatures from 2 to 600 K. The Curie temperature decreases to zero as the composition approaches the x =1/3 value. The effective moment calculated from both the high temperature portion of the data utilizing a Curie–Weiss fit and from the saturation moment decreases to very near zero as the x =1/3 composition is approached. This behavior is explained by the existence of magnetic clusters of Fe atoms. Fe atoms on the V site in Fe 2 VAl cause the eight neighboring Fe atoms to become magnetically active thereby forming clusters of nine magnetic Fe atoms.

The perovskite-based system (La1−xPrx)Ba2Cu2NbO8 has been synthesized for 0≤x≤1 and characterized using x-ray diffraction and magnetization measurements. Lattice parameters determined by Rietveld refinement are given as a function of composition. Antiferromagnetic ordering of the Pr sublattice is observed for x≥0.5, the Neel temperature (TN) is observed to increase linearly with Pr content, and the previously reported TN of 12 K for PrBa2Cu2NbO8 is confirmed. These results are interpreted in terms of established Pr magnetism in PrBa2Cu2NbO8 and similar magnetism in other well-documented high-Tc cuprate structures.

We report the first investigation of two-dimensional magnetic polarons formed from excitons localized in very thin nonmagnetic CdTe quantum wells confined by Cd1−xMnxTe diluted-magnetic-semiconductor barriers. Analysis of the Stokes shift of the exciton luminescence peak under resonance excitation, which is a dramatically decreasing function of temperature and magnetic field, allows us to determine the magnetic polaron energy. The polaron energy measured as a function of quantum well width is found to be 25 meV in a 6 A thick quantum well and to vanish in wells thicker than 30 A.

The transition from two- to three-dimensional character of the exciton wave function is demonstrated in CdTe/Cd 0.75 Mn 0.25 Te single quantum wells or superlattices by resonance reflectivity measurements of the heavy-hole exciton oscillator strength as a function of the well width or period. A strong increase of the oscillator strength by a factor of 30 is found for 2D-excitons confined to 15 A thick quantum wells. In thinner wells the oscillator strength decreases as a result of substantial penetration of the exciton wave function into the barrier layers. A similar nonmonotonic behaviour is observed in superlattices (SL) which indicates the formation of the electron miniband in periods less than 60 A. A pronounced effect of an external magnetic field on the oscillator strength of Zeeman patterns is found in the short-period SLs signaling for the low-energy component a trend towards a type II SL transition.

A comparison has been made of the Raman scattering from YBa2Cu3O7 crystals that were grown in gold and zirconia crucibles and that contain 0.74 atomic-% gold and ∼0.009 atomic-% zirconium, respectively. Differences exist in the absolute values of the phonon line widths in the two types of crystals. However, gold substitution is found to 3ave littel effect on the temperature dependence of the line widths of the Ag phonons since nearly the same trends are observed in both types of crystals. In particular, the 340-cm−1 phonon becomes significantly more symmetric and sharper below Tc, in distinct disagreement with the results of other researchers. The line widths of the Ag phonons support a superconducting energy gap bounded between 440 and 500 cm−1 (2Δ = 6.8 − 7.7kBTc).

We report the first experimental observation of free magnetic polarons in diluted magnetic semiconductor quantum wells. CdTe/Cd 0.78Mn0.22Te multiple quantum well structures with quantum well widths up to 100 A were investigated by reflection, photoluminescence and photoluminescence excitation spectroscopy at low temperatures and in magnetic fields. Free and bound magnetic polaron energies were determined by the suppression of polaron formation with increasing temperature and in external magnetic fields.

The effects of hydrostatic pressure to 21 kbar on a series of thirteen ternary compounds in the system (Er 1−x Ho x )Rh 4 B 4 are presented. For all compositions, both the superconducting and magnetic interactions are strengthened by the application of external pressure. Maximum sensitivity to pressure of both critical temperature is attained at the critical concentration (x cr ≈ 0.89) for the disappearance of superconductivity.

Temperature dependent 151Eu Mossbauer spectroscopy experiments on the high Tc≧90K superconductor EuBa2Cu3O7 in the range of 4.2K < T < 300K display evidence of Eu3+ site only. No evidence of Eu2+ sites is observed. Variation of isomer-shift σ(T) and recoil-free-fraction f(T) shows that the mean square displacement (lnf) and mean square velocity (σ) of the Eu3+ site are both characterized by a Debye temperature θD=280(5)K. No discernible evidence of a phonon mediated structural transition as a precursor to Tc is observed in the temperature range examined.

A pronounced lambda-type specific heat anomaly in the superconducting state is reported for Gd-rich pseudoternary compounds (La1-xGdx)1.0Mo6Se8. The anomaly is very similar to that previously reported for the compound Gd1.2Mo6Se8. Both the temperature of the lambda anomaly (≈ 3.5 K) and the Curie-Weiss temperature were found to be nearly independent of x. In addition, evidence for the occurence of magnetic ordering at 0.8 K in Gd1.2Mo6Se8 is presented. These observations support our earlier conjecture that the lambda anomaly at 3.5 K does not arise from magnetic ordering of the Gd3+ ions. The anomaly appears instead to be due to a different type of phase transition which is associated with the presence of the localized 4f electrons of the Gd3+ ions, but the exact nature of the transition remains to be established.

The superconducting transition temperature and its dependence on hydrostatic pressure to 22 kbar have been determined for a series of (La, Ce)Ru2 alloys. The variations of these quantities with composition are found to be generally related; however, specific irregularities in the curve of dTc/dp versus composition are not reflected in the smooth variation of the transition temperature Tc. Some features of dTc/dp may be correlated with the occurrence of a cubic-tetragonal transformation at low temperatures.

It is shown that the normal collisions, which are much rarer than the electron-impurity scattering, affect qualitatively the momentum transfer from the electrons to the metal surface that may lead to a temperature minimum in resistivity. In a sample with the thickness greater than electron-impurity mean free path, the isotropy of the Fermi surface and scattering processes is sufficient for the minimum to appear. In a thin wire of an arbitrary shaped cross-section, the minimum is possible if the normal electron-phonon collisions predominate over the electron- electron ones. The expressions derived here essentially differ from earlier theoretical results and permit a qualitative explanation of the temperature minimum in K.

The pressure dependence of the superconducting transition temperature, T c , is determined for eight metallic glasses in the series (Nb 1−x Ta x ) 55 T 45 , where T Rh, Ir. From these data we estimate the Gruneisen parameter, γ G , and the volume dependence of the electron-phonon coupling constant, λ. Pressure is observed to affect T c through both γ G and λ.