Intrinsic and extrinsic magnetic susceptibilities of some TCNQ complexes

The magnetic susceptibilities (χ) of quinolinium·(TCNQ)₂, N-methyl phenazinium·TCNQ and Li·TCNQ were measured from 2 to 300 K and are discussed in connection with the low-temperature specific heats (C) measured by other authors, χ is decomposed into three parts: χ_d the temperature-independent part, χ_c, Curie-Weiss type paramagnetism, and χ_p, the remainder. Correspondingly, C is composed of three terms, γT, H/T² and αT³. The electronic state of these substances is discussed in terms of each type of susceptibility.The model, on which the above separation of χ and C is based, defines two types of electrons: localized electrons associated with a magnetic moment and band electrons. Though this model is useful phenomenologically, it is shown that the analysis of χ on the basis of this model indicates less band electrons and more localized electrons or stronger magnetic interactions than does that of C.     

Optical absorption in a heavily doped semiconductor with a narrow forbidden band

The coefficient of interband absorption in a heavily doped, strongly compensated semiconductor with a narrow forbidden band was calculated for emission frequencies ?ω which are smaller than the width? _g of the forbidden band. If the width of the forbidden band is smaller than the characteristic energy w₀ of the random field produced by randomly distributed impurities, the optical absorption gap is missing and the coefficient of absorption increases with the frequency, with the increase being basically proportional toω.     

Polarized photoluminescence from bound magnetic polarons in (Cd,Mn) Se

Luminescence from Cd_1-xMn_xSe, with x～10^-1, shows strong circular polarization in the presence of a weak magnetic field. The polarization saturates at fields much smaller than does the magnetization. The carrier-Mn²⁺ exchange interaction is responsible for the field and temperature dependence of the polarization. At high temperatures, the polarization is similar to that inferred from band splittings; at lower temperatures, it is modified by bound magnetic polaron effects and a spin diffusion bottleneck.     

Diamagnetic properties of tetrahedrally coordinated Ge1-xSx and Ge1-xSex amorphous alloys

Measurements of the diamagnetic susceptibility χ at room temperature are reported for Ge_1-xS_x and Ge_1-xSe_x amorphous alloys as a function of composition. The composition dependence of χ is shown to reflect the corresponding changes in the average gap E_g and it is concluded that the dia diamagnetic enhancement observed in tetrahedrally bonded amorphous semiconductors is caused by a decrease in the interband matrix element in the Van-Vleck paramagnetic susceptibility term with bond angle distortion rather than changes in E_g.     

Magnetic absorption of hexagonal crystals CdSe in strong and weak fields: Quasi-cubic approximation

The spectra of ultrathin free samples of hexagonal CdSe in a magnetic field up to 8 T are studied at 1.7 K. The fan-shaped diagram contains information on weak (the Zeeman effect and diamagnetic shift), as well as strong fields (transitions between Landau levels). As a result of the application of two theoretical models for combined interpretation of strong-and weak-field experimental data, two sets of (band and polaron) parameters are calculated for hexagonal CdSe in the quasi-cubic approximation. The values of the obtained polaron/band parameters are: the electron effective mass m _e =0.125/0.116m ₀, the Luttinger parameters γ₁=1.5/1.72, γ=0.29/0.37, κ=?0.63, and the effective electron g-factor g _e =0.7.     

Conductivity in a disordered medium and carrier localization in weakly doped lanthanum manganites

The dc and 9.2-GHz electrical resistivities and magnetoresistance observed in La_1?xA_xMnO₃ crystals (A=Sr, Ce, x≤0.1) in the temperature interval 77–300 K are accounted for by the contributions due to carriers, both nonlocalized and localized in the valence-band tail and near the Fermi level. The localized-state tail extends to a depth of 0.15–0.25 eV inside the band gap, and the hopping activation energy varies from 0.06 to 0.15 eV, depending on the sample composition. Within the temperature region where magnetic ordering sets in, the variations of the electrical resistivity and magnetoresistance with temperature and magnetic field are caused by variations in the carrier mobility and concentration.     

Elastic-stress relaxation in compacted nanocrystalline CuO

The magnetic properties of two types of nanocrystalline antiferromagnetic CuO samples, namely, dense nanoceramics and loose powders, were studied. For nanomaterials with smaller particles, the magnetic susceptibility χ was shown to increase with a decrease in temperature T < T_N. The increase in χ in both series of samples is related to the disordering of Cu²⁺ spins at the surfaces of nanoparticles. The magnetic properties of nanopowders characterize the properties of isolated nanoparticles. In a dense nanoceramic, the size effect is compensated for by the interaction between nanoparticles. The magnetic properties of nanoceramics are determined by elastic stresses induced by an external action. Elastic-stress relaxation results in the recovery of magnetic order and decreases the magnetic susceptibility.     

Response of commercial window glass to gamma doses

This work reports experimental results of an effort undertaken to identify and characterize the radiation-induced defects created during gamma (γ)-irradiation of commercial glass on the basis of optical absorption measurements performed before and after irradiation. It is assumed that the induced absorption band formed after γ-irradiation of soda-lime-silica (SLS) glasses are created by some hole-type color centers related with non-bridging oxygen ions (NBO⁻) located in different surroundings.Results have been discussed taking into consideration the presence of iron as impurity in the glass structure. It is well known that the absorption bands of Fe³⁺ in the visible range is at 420-440 nm, in this study the band at 430 nm was followed. Also, the optical gap variations (ΔE_opt) induced by γ-irradiation were investigated.Moreover, the study illustrated that the optical absorption sensitivity and the mechanism of fading either at room or elevated temperature has been discussed in relation to successive irradiation doses, dose rate and thickness. The results are discussed on the basis of the annihilation mechanisms of induced irradiation defects.     

Non-stoichiometry and temperature-dependent magnetic susceptibility of CoO

Magnetic susceptibility χ of several CoO samples has been measured in the temperature range of 4.2–350 K. Below about 140 K, and additional contribution to χ, different for different samples, is observed. It is proposed that this excess susceptibility is due to an uncompensated moment resulting from deviations from stoichimetry. The estimated χ values for a stoichiometric CoO at T_N and absolute zero agree with Tachiki's calculations.     

The heat capacity of Th and Th4H15 in the temperature range above 2 K

Heat capacity C of pure Th and Th₄H₁₅ was measured in the temperature range above 2 K. In the case of Th₄H₁₅ the superconducting anomaly was observed in the temperature slope of C at T < 7.6 K. For Th₄H₁₅ the γ-co-efficient of electronic heat capacity is smaller and the Debye-temperature larger than that of pure Th, respectively.     

Specific heat anomaly of single phase YBa2Cu3O7-δ at superconducting transition temperature

The specific heat of single phase YBa₂Cu₃O_7-δ has been measured using non-adiabatic method between 4.2K and 120K. There is a specific heat anomaly Δc at 90K (about 3.2% of total specific heat) approximately, due to superconducting transition. From the measured value of ΔC and transition temperature T_c, the electronic density of state at Fermi level N(E_F) and Sommerfeld parameter γ calculated are 2.55±0.30states/eV.Cu-atom and 2.77±0.30 mJ/mole.K², respectively. The experimental result of N(E_F) is consistent with that of the band calculation by Mattheiss. The Debye temperature above T_c in this material deduced from Debye function is about 340K. Below 20K, the relation C=γ'T+βT³ is satisfied. But the value of γ' is smaller. That means, most of the electrons have formed superconducting Cooper pairs which give no contribution to specific heat below 20K.     

Comparison between the magnetic susceptibilities of Pd1−xAgx and single phase PdHn

The rapid decrease of the isothermal magnetic susceptibility χ of single phase PdH_n with n ( = atomic ratio H/Pd) above the critical temperature T_c = 564 differs from that of the magnetically similar single phase system Pd_1−xAg_x (x: silver mole fraction) at the same temperature and at equal valence electron concentrations (n = x), i.e. χ (PdH_n)−χ(Pd_1−xAg_x) <0. By use of a semiphenomenological susceptibility ansatz related to the nonideal solution behaviour of H (Ag) in Pd the susceptibility difference is interpreted as an electronic excess effect.The analysis of the steep descent of the magnetic susceptibility also applies to the Pd-rich side of PdH_n in the subcritical temperature region (so-called α-phase) and can be supported by ¹⁰⁵Pd Knight shift data at 348 K.     

Effect of spin-fluctuations on the temperature dependence of electrical resistivity in transition alloys

Two recent theories of spin-fluctuations in metals are generalized to concentrated transition binary alloys. It is shown that in these alloys the effect of spin-fluctuations can give to a negative T-coefficient of resistance d?/dT.     

On the pressure dependence of the effective ionic charge of cesium halides

The importance of temperature effects in the use of the second Szigeti relation to calculate the volume dependence of the effective ionic charge of cesium halide crystals is studied. The effect obtained is larger than the one for alkali halide crystals of the NaCl structure. Positive values of (? ln s/? In v) are obtained using low temperature experimental data with the Grüineisen parameter γ_t(T → 0K) calculated using the generalized first Szigeti relation. Values of γ_t are also obtained with a rigid ion model and they differ little from the previous ones.     

The level structure of the 153Gd nucleus studied in the 150Sm(α, n)153Gd reaction

The level structure of ¹⁵³Gd has been studied by means of the ¹⁵⁰Sm(α, n)¹⁵³Gd reaction. The experiment included measurements of γ-γ coincidences, γ-angular distributions, γ-ray yield at 17 MeV and 19 MeV beam energy, and γ-ray multiplicities. Favoured and unfavoured members of the positive-parity i_13,2, band were identified. States belonging to the h_9,2 and f_7,2 band structures have been located.Surprisingly low multiplicity numbers were deduced for ₁₅₃Gd γ-rays. This may indicate that the (α, n) reaction is not a pure compound reaction. The level structure of ¹⁵³Gd has been compared to the known structure of other odd-mass N = 89 nuclei, and a close similarity is found.The positive-parity band structure has been compared to calculations with the pairing-plus-recoil model. Good agreement is obtained without any ad hoc Coriolis attenuation.     

On the dynamic conductivity for an electron-impurity system

The correlation function formula for the dynamic conductivity of a system of non-interacting electrons in the field of impurities is analyzed in terms of proper connected diagrams. By selecting those diagrams appropriate in the region of weak coupling and low impurity concentration, a set of coupled equations for the energy broadening γ (ω, ε, n_s) and the energy shift Δ(ω, ε, n_s) is derived, where both γ and Δ depend on the frequency ω of a probing field, the energy ε of the electron, and the concentration, n_g, of impurities. With the assumption of a finite range potential, these equations are solved. It is found that γ (ω, n_s) is smaller than that extrapolated value which the conventional expression γ₀ for the low-concentration collision frequency would predict, in the entire region studied, that the difference γ₀-γ becomes appreciable when the ratio of the average time between scatterings, τ_c, to the average duration of a scattering, τ_d, is 100 or less, that γ (ω, n_s) decreases monotonically from its static value γ (0, n_s), and becomes vanishingly small in the region ω≈1/τ_d, and that in the static limit (ω=0), γ=γ₀[1?(2/π) (γ₀τ_d)+…], that the energy shift Δ is positive, and increases from 0 and reach a peak of magnitude γ₀ as ω is raised from 0. By using the γ and Δ obtained, the dynamic conductivity σ(ω, n_s) for degenerated electrons is calculated. The deviation, σ-σ₀, from the conventional expression σ₀=(?i) (n_ee²/M) [ω-iΓ₀]^?1, (n_e]=number density of electrons), for 0°K, is appreciable when the ratio τ_c/τ_d is 100 or less. The field-term correction, which arises from the modification of the scattering due to the probing field, is found to be negligible in the entire region studied.     

Das Konversionselektronenspektrum von196Pt nach Neutroneneinfang

The superconducting conversion electron analyser SULEIKA has been used to measure the electron spectrum of¹⁹⁶Pt after neutron capture in¹⁹⁵Pt. The experimental arrangement is described. Energies and intensities of 20K-, 10L- and 3M-lines are reported and, using known γ-data as well asK toL ratios, multipolarities are determined.     

Specific heat of pure graphite in the ultra-quantum limit region

We calculate the electronic specific heat of pure graphite in the ultraquantum limit region for fields between 60 and 200 kG, at very low temperatures, using the Slonczewski-Weiss band model with values of the energy-band parameters which are in agreement with recent magneto-reflection experiments. The effect of trigonal warping of the Fermi surfaces associated with the parameter γ₃ is neglected in the calculation. Our results show that, for most of the range of fields considered, the electronic specific heat C is very nearly proportional to both the magnetic field strength H and the temperature T, according to the relation C ≈ αHT with a coefficient α of about 0.091 μJ/g-at. K²kG. The results also indicate that, at the upper end of the magnetic field range, the C(H) curves, at a given T, depart progressively, though slightly, from linearity with increasing H.     

χ particle production in π−p collisions at 38 GeV/c

The production of χ particles in the reaction π^?p → χ + … has been studied near threshold. The measurements have been performed at the 70 GeV IHEP proton synchrotron using the hodoscope spectrometer GAMS-2000. The χ particles have been identified through their decay χ → J/ψ + γ, J/ψ → e⁺e^?. In the region X_F ?0.4 the fraction of obsered J/ψ particles which is obtained via the decay of χ states is 0.44 ± 0.16. The χ longitudinal and transverse momentum distributions are similar to those obtained for J/ψ. The inclusive production cross section of χ particles (³P₁ and ³P₂ states) at 38 GeV/c is σ_XF>0 (π^?p → χ + …) = (28±11) nb.     

An anomaly in the magnetic susceptibility of the Mg1−x CuxO solid solutions with 0.01≤x≤0.20

The problem of localized superconductivity has motivated the preparation of Mg_1−x Cu_xO solid solutions with NaCl structure and 0.01≤x≤0.20, as well as a study of the magnetization and magnetic susceptibility χ in the 2–400 K temperature range and in magnetic fields of up to 5 T. The temperature dependence of χ is described for all compositions by the Curie-Weiss law, χ = C/(T − θ), where the constant C is close to the value calculated for each composition for μ_eff = 1.7–1.9μ_B, and θ is close to zero. For T < 30 K, χ(T) deviates for all compositions toward lower χ, which can be attributed to magnetic ordering of exchange-coupled clusters in the solid solution. At T∼320–330 K, an anomaly of a diamagnetic type, i.e., a decrease of χ by 6–30% of its paramagnetic value, has been observed for all compositions against the background of the generally paramagnetic χ(T). A discussion is presented of alternative reasons for this anomaly and of its possible connection with localized superconductivity. __________ Translated from Fizika Tverdogo Tela, Vol. 42, No. 4, 2000, pp. 701–703. Original Russian Text Copyright ? 2000 by Samokhvalov, Arbuzova, Viglin, Naumov, Smolyak, Korolev, Lobachevskaya.