Magnetic Specific Heat of Heavily p-Type Doped (Zn,Mn)Te:P

The magnetic contribution to the specific heat of bulk crystals of Zn_1?x Mn _x Te ( x = 0.03) heavily (up to 10¹⁹ cm^?3) p-type doped with P is studied over the temperature range 0.5–15 K and magnetic field range 0–3 T. The magnetic specific heat observed at zero magnetic field indicates that a substantial part of the magnetic ions has the degeneracy of their magnetic ground state lifted by d–d and p–d exchange interactions. The effect increases for doped and annealed samples with higher concentration of conducting holes. We have also carried out a theoretical analysis that takes into account the contributions due to small magnetic clusters, single magnetic ions in crystal field of distorted crystal lattice, and low energy excitations of the p–d exchange-coupled system of local moments and carriers.     

Specific Heat Jump at Tc of High Tc Superconductors: Effect of Van Hove Singularity

In the BCS framework, exact expressions for the ratio between the jump in the specific heat at T _c and the normal phase specific heat are derived within the Van Hove singularity scenario. Analytical results are obtained for an isotropic s-wave and anisotropic d-wave pairing symmetries. Graphical solutions of the ratio as functions of _D /T _c and E _F /T _c , where _D is the cutoff energy and E _F is the Fermi energy, show significant deviations from the BCS value of 1.43.     

Spin Carrier Exchange Interactions in (Ga,Mn)N and (Zn,Co)O Wide Band Gap Diluted Magnetic Semiconductor Epilayers

(Ga,Mn)N and (Zn,Co)O wide band gap diluted magnetic semiconductor epilayers have been investigated by magneto-optical spectroscopy. In both cases, absorption bands observed below the energy gap allow us to study the nature of the valence and spin state of the incorporated magnetic element. Exchange interactions between magnetic ions and carriers can be observed by analyzing the magnetic circular dichroism in transmission or the exciton Zeeman splitting in reflection for (Zn,Co)O. A first estimation of the exchange integrals can be given for both materials.     

Photoinduced Magnetization Rotation and Precessional Motion of Magnetization in Ferromagnetic (Ga,Mn)As

Dynamics of photoinduced magnetization have been studied in ferromagnetic semiconductor (Ga,Mn)As thin films by time-resolved polar Kerr rotation. Ultrafast (150 fs) magnetization rotation has been realized using both chirality of excitation light and p–d exchange interaction. We also report on the occurrence of photoinduced magnetization precession in longer time domain. This is initiated by a change in hole concentration and resultant change in magnetic anisotropy. The overall behaviors of these photoinduced magnetization dynamics are discussed.     

Influence of Codoping on the Magnetoresistance of Paramagnetic (Ga,Mn)As

We studied the correlation between magnetoresistance (MR) effects and the type of conducti- vity in paramagnetic Ga_1–x Mn _x As with x < 0.5%. Series of samples of (Ga,Mn)As with different codoping levels of Te have been prepared by metal-organic vapor-phase epitaxy (MOVPE). With increasing Mn-content from doping levels to x = 0.5% in paramagnetic Ga_1–x Mn _x As, the MR at 1.6 K changes continuously from positive to strongly negative. This manifests the complex interplay between p–d exchange induced valence band splitting and the metal–insulator transition. Codoping with Te leads eventually to a dominant conduction band transport. It is characterized by a small negative contribution at low magnetic fields to the parabolic MR similar to that found in highly n-doped diamagnetic semiconductors. It shows that the Mn-induced conduction band splitting is much smaller than the valence band splitting, i.e., |N₀| |N₀|.     

Magnetic and Electrical Properties of Random and Digital Alloys of GaSb:Mn

We have investigated the effect of Sb/Ga flux ratio on the magnetic and electronic properties of Mn-incorporated GaSb random and digital alloys grown by low-temperature molecular beam epitaxy. The magnetic and magnetotransport properties of Ga_1–xMn_xSb random alloys are strongly dependent on Sb/Ga flux ratio. Clear square-like hysteresis loops were observed for Sb/Ga flux ratios between 4.60 and 5.25. The coercive field and negative magnetoresistance increase with decreasing Sb/Ga flux ratio, while the Curie temperature remains constant at approximately 23 K, with no systematic dependence on the hole density. In contrast, the Curie temperatures for the GaSb:Mn digital alloys with different Mn surface coverages depend significantly on the Sb/Ga flux ratio, and it is also directly correlated with the hole density.     

The Thermal Conductivity, Thermal Diffusivity, and Specific Heat of Liquid n-Pentane

The thermal conductivity and thermal diffusivity of liquid n-pentane have been measured over the temperature range from 293 to 428 K at pressures from 3.5 to 35 MPa using a transient hot-wire instrument. It was determined that the results were influenced by fluid thermal radiation, and a new expression for this effect is presented. The uncertainty of the experimental results is estimated to be better than ±0.5% for thermal conductivity and ±2% for thermal diffusivity. The results, corrected for fluid thermal radiation, are correlated as functions of temperature and density with a maximum uncertainty of ±2% for thermal conductivity and ±4% for thermal diffusivity. Derived values of the isobaric specific heat are also given.     

Hc2 of MgCNi3 Determined from the Specific Heat and Resistivity Measurements

H _c2 of MgCNi₃ has been determined from the specific heat C and resistivity measurements in the same sample. The results from are nearly identical with those determined from the anomaly in C. Furthermore, utilizing the relation (H) H and the value of d/dH, the obtained value of H _c2 is the same as that by the WHH model, if the spin paramagnetic effect and the spin–orbit interaction are taken into account. The results of this comparison have strong implications on the order parameter of MgCNi₃.     

Temperature Peculiarities of Magnetic Anisotropy in (Ga,Mn)As: The Role of the Hole Concentration

It is demonstrated by SQUID measurements that (Ga,Mn)As films can exhibit perpendicular easy axis at low temperatures, even under compressive strain, provided that the hole concentration is sufficiently small. In such films, the easy axis assume a standard in-plane orientation when the temperature is increased towards the Curie temperature. The findings are shown to corroborate the predictions of the mean-field Zener model for strained (III,Mn)V ferromagnetic semiconductors.     

Magnetic properties of RRh3B2(R=La,Ce, Nd,Gd) compounds

The¹¹Bnmr results on RRh₃B₂(R=La, Ce, Nd and Gd) are reported. For CeRh₃B₂, specific heat and electrical resistivity are reported. From a comparative study of the¹¹Bnmr Knight shifts and the spin lattice relaxation times of these compounds it is shown that in CeRh₃B₂, there is strong hybridization of 4f states with the conduction electrons. A local moment on Ce with admixture of 4f and 5d–6s orbitals is suggested.     

Synthesis and characterization of a novel poly(N-vinyl)-3-[p-nitrophenylazo]carbazolyl-CdS nanocomposites through chemical hybridization

A novel bi-functional photorefractive (PR) poly(N-vinyl)-3-[p-nitrophenylazo]carbazolyl with carbazolyl fragments and chromophoric azophenyl was synthesized by a post azo coupling reaction and characterized by ¹H NMR, elemental analysis, UV–Vis absorption and FTIR spectroscopy. Then chemical hybridized poly(N-vinyl)-3-[p-nitrophenylazo]carbazolyl-CdS nanocomposites with different molar ratio of CdS to poly(N-vinyl)-3-[p-nitrophenylazo]carbazolyl were prepared. It was confirmed that the CdS particles had a nanoscale size and quantum confinement effect adopting transmission electron microscopy and UV–Vis absorption spectroscopy. The generation of photocurrent on illumination and photoconductive properties of the nanocomposites were studied. Significant enhancement in photoconductivity induced by the chemical doping of CdS in poly(N-vinyl)-3-[p-nitrophenylazo]carbazolyl has also been demonstrated.     

Volumetric and Thermodynamic Properties of Liquid Mixtures of 2-n-Butoxyethanol with Water

p–V–T data for six compositions of 2-n-butoxyethanol (BE) and water have been obtained in the form of volume ratios at several temperatures in the range 278.15 to 353.13 K at pressures from atmospheric to 347 MPa or higher. One of the compositions is in the region where two phases exist at certain temperatures, while two compositions are near the boundary of that region. Densities at atmospheric pressure in a temperature range similar to that for the p–V–T data are also reported. Isothermal compressibilities, isobaric expansivities, and changes in the isobaric heat capacity have been calculated from the volumetric data for pressures up to 300 MPa. The values of normalized volume fluctuations obtained from the data at 0.1 MPa approach those of water for conditions which are close to those for phase separation in this system. Such behavior is not observed at 100 MPa, where such separation is suppressed.     

Influence of doping on the electronic structure of (La, Sr)2CuO4

High-statistics (>4 × 10⁸ counts), room-temperature measurements of the electron-positron momentum density of La_2–x Sr _x CuO₄ have been performed for samples with Sr concentrations of x=0.0, 0.1, 0.13, and 0.2. These spectra have been analyzed in conjunction with theoretical calculations of the electron-positron momentum density. The metallic samples show features consistent with the presence of a Fermi surface, but its evolution with increasing Sr concentration does not follow the predictions of band theory. These results may indicate the effects of electron-electron correlation on the electron momentum distribution in the Cu-O plane.     

Is the tetragonal overdoped phase (La, Sr)2CuO4 superconductive?

Comparative studies of Meissner and shielding processes have been performed on variously sized samples of the solid solution (La_1–x Sr _x )₂CuO₄: (polycrystalline, powder, and single-crystalline) under various magnetic fields in the range 0.03–10 Oe. Considering the kinetics of the two processes, this systematic approach has indicated that the observed Meissner signal can be significantly low with the sample still being wholly superconductive. Based on this comparative study, the tetragonal region of (La_1–x Sr _x )₂CuO₄ withx greater than 0.105 has been concluded to be superconductive, suggesting the nonessential involvement of the buckling of the Cu-O-Cu-O bond in the CuO₂ layer in the manifestation of superconductivity.     

Transport in Vortex State of d-Wave Superconductors at Zero Temperature: Wiedemann–Franz Violation

We show that the Wiedemann–Franz law is violated at zero temperature in the vortex state of a d-wave BCS superconductor with isotropic impurity scattering. We use a semiclassical approach to include the Doppler shift experienced by the quasiparticles due to the circulating supercurrents and consider as well the Andreev scattering from an array of vortices assumed to be randomly distributed. We also show that the vertex corrections to the electric conductivity, which can be large when there is significant anisotropy in the impurity scattering, become unimportant as the magnetic field is increased. For the thermal conductivity, the corrections remain negligible as in the absence of a magnetic field.     

Origin of Spin-Glass Behavior of Zn1 ? xMnxO

Alternating current susceptibility has been studied for polycrystalline Zn_{1 – x} Mn _x O. Stoichiometric samples demonstrate Curie–Weiss behavior, which indicates mostly antiferromagnetic interactions. Magnetic susceptibility can be described by a diluted Heisenberg magnet model developed for semimagnetic semiconductors. High-pressure oxygen annealing induces spin-glass like behavior in Zn_{1 – x} Mn _x O by precipitation of ZnMnO₃ in the paramagnetic matrix.     

Microstructures and thermoelectric properties of p-type pseudo-binary AgxBi0.5Sb1.5−xTe3 (x = 0.05–0.4) alloys prepared by cold pressing

The p-type pseudo-binary Ag_xBi_0.5Sb_1.5−xTe₃ (x = 0.05–0.4) alloys were prepared by cold pressing. The thermal conductivities (κ) were calculated from the values of heat capacities, densities and thermal diffusivities measured, and range approximately from 0.66 to 0.56 (W K^− 1 m^− 1) for the Ag_xBi_0.5Sb_1.5−xTe₃ alloy with molar fraction x being 0.4. Combining with the electrical properties obtained in the previous study, the maximum dimensionless figure of merit ZT of 1.1 was obtained at the temperature of 558 K.