High Frequency Transport Properties of YBCO: Extrinsic Versus Intrinsic d-Wave Properties

In good superconducting YBCO films, the surface impedance Z(T,ω,B)=Z_int(T,ωB)+Z_res(T,ωB) is dominated for T T _c/2 and B～0 by intrinsic properties, which are difficult to improve. Below T _c/2, Z _res usually dominates over Z, and below 0.9 T _c, Z(T,ω,B) increases with field, both are, up till now, explained by extrinsic properties related to extrinsic and intrinsic surfaces. The latter are named weak or strong links (WSL), into which around B _c1J for ω₀ ^J » ω₀ ^A Josephson fluxons (JF) enter, where B_c1J « B_c1 holds with B_c1 the lower critical field of Abrikosov fluxon (AF) with ω₀ ^A ～ MHz their nucleation or pinning frequency. Below fields ?B _C1 and below the pinning or nucleation frequency ω₀ ^J ～ THz hysteresis losses increase Z=R+iX nonlinearly with r(T,ω)=δ X/δ R～2 with the surface resistance R and the surface reactance X. The nonlinearities decrease toward B _c1J to (small) oscillation of JF yielding r(T,ω) δ ω₀ ^J (T)/ω . Those Z nonlinearities yield harmonics or intermodulation products IMD(T). Below B _c1J new types of nonlinearities relate to d-wave properties of HTS. Either nonlinear Meissner effect (NME) and anomalous Meissner effect (AME) at internal or external surfaces are proposed with r ? 1, observed by harmonic generation and by specific IMD(T, B) dependencies being identified recently. New developments in theory and experiment and procedures to separate extrinsic from intrinsic properties will be analyzed.     

Fish-Tail Effect and Its Evolution Under Neutron Irradiation in Li-Doped YBa2Cu3O7−x

The evolution of the critical current density of Li-doped YBa₂Cu₃O_7?x polycrystalline samples submitted to neutron irradiation is investigated as function of magnetic field (0 ≤ B ≤ 6 T) temperature (5 ≤ T ≤ 85 K) and neutron fluence (0 ≤ Φ ≤ 9.98 × 10¹⁷ cm^?2). At fluences lower than 10¹⁷ cm^?2, a second peak in j _s vs. B dependence is present (fish-tail effect). Its magnitude decreases with increasing the fluence. Above 10¹⁷ cm^?2, the second peak of current density completely disappears; instead, the logarithmic susceptibility shows a second peak at a certain field B _infl. A dependence of B _infl on fluence is proposed.     

From Manipulation of Giant Magnetoimpedance in Thin Wires to Industrial Applications

We present results on our studies of soft magnetic properties and Giant magnetoimpedance, GMI, effect in thin microwires at elevated frequencies paying special attention to tailoring the GMI effect and achievement of high GMI effect with low hysteretic behavior. We measured magnetic field, H, dependence of real part, of the longitudinal wire impedance up to frequency, f, 4 GHz in Co-rich microwires. Amorphous microwires of appropriate composition exhibit extremely soft magnetic properties with low coercivity (generally below 10 A/m) with well defined magnetic anisotropy field, H _k . We report a number of interesting for sensor applications phenomena such as stress-impedance effect and stress sensibility of overall hysteresis loop shape. Field dependence of the off-diagonal voltage response of pulsed GMI effect in nearly-zero magnetostriction (λ _s≈?3×10^?7) microwires exhibits anti-symmetrical shape, suitable for industrial applications. We observed that the magnetic field dependence of GMI ratio can be tailored either controlling magnetoelastic anisotropy of as-prepared microwires or by heat treatment. Composite character of such microwires results in the appearance of additional magnetoelastic anisotropy. We found that if the surface anisotropy is not circumferential, then the magnetization, and consequently, the MI curve Z(H) present hysteresis. This hysteresis can be suppressed by application of sufficiently high DC bias current I _B that creates a circumferential bias field H _B.     

The Influence of Vanadium on Magnetism and Magnetocaloric Properties of Fe 8 0 − x V x B12Si8 (x = 8, 10, and 13.7) Amorphous Alloys

Amorphous soft magnetic Fe_80?x V _x B₁₂Si₈ ribbons (0 ≤ x ≤ 14) have been fabricated by melt spinning technique, and their magnetic and magnetocaloric properties have been studied. The value of magnetocaloric effect has been determined from the measurements of magnetization as a function of temperature and an external magnetic field. The addition of vanadium to the ternary Fe₈₀B₁₂Si₈ alloy results in a decrease of the Curie temperature of amorphous alloys, T _C, from 473.5 to 335 K. With an increasing V content, the average magnetic moment of Fe atom and the magnetic entropy change also decrease. Fe_66.3V_13.7B₁₂Si₈ alloy exhibits the highest refrigeration capacity of 93.7 J kg^?1 and moderate peak magnetic entropy of 1.034 J kg^?1 K^?1 (T _C = 335 K) under the maximum applied field of 2 T. The results from this work showed that V containing amorphous alloy 13.7 at. % is an interesting material and potential candidate for magnetic refrigerants working near room temperature. The observed ?ΔS_M ^max values compare favorably with other amorphous Fe-based alloys.     

Electrical transport in copper chromite catalyst

The electrical conductivity, σ, and thermoelectric power, S, of copper chromite (CuCr₂O₄) are reported in the temperature range 295 to 815 K. A break (T _B) in the slope of the plot of log σ against T ^?1 was observed around 556 K. Apart from this break, the curves are linear, and their slopes correspond to activation energies of 0.60 eV (T _B<556 K) and 1.22 eV (T _B>556 K). A break (T′ _B) in the slope of the -S against T ^?1 plot was also observed round 556 K. Apart from the break at this temperature, the S against T ^?1 curves are linear. At T′ _B>556, S can be expressed by the relation $$S = - \left[ {\left( {\frac{{0.65 eV}}{{{\text{2}}eT}}} \right) + (0.42) mV K^{ - {\text{1}}} } \right]$$ The mechanism involved in the electrical transport is the hopping of holes from Cr⁴⁺ centres to neighbouring Cr³⁺ ions. The typical hopping mobility of the holes is of the order of 10⁶ m² V^?1 sec^?1. The mobility activation energy of the holes in CuCr₂O₄ decreases with temperature due to the smoothing of the potential barriers between Cr⁴⁺ and Cr³⁺ sites.     

Dependence of Superconductivity and Its Weakly Linked Behavior in Bulk LaO1?x F x FeAs on F Doping

Samples of oxypnictide compound LaO_1?x F _x FeAs, with x=0.15 and 0.2 corresponding to over- and highly over-doped compositions, respectively, were prepared by solid-state reaction. We present their characterization by XRD and HRTEM, as well as resistivity ??(T), magnetization M(B) and microwave modulated absorption (MMA) response between 4.2?C300?K and applied fields B=0?C8?T. With change in?x, both the superconducting and magnetic behavior of the samples shows an interesting pattern. The ??magnetic anomaly?? at T??130?K, observed in M(T) for x=0, instead of getting totally suppressed shows a tendency to reappear in x=0.2 sample. Both samples typically show ??(300?K)>2.8×10^?3????cm and critical current density J _c(5?K, 1?T)<2×10⁷?A/m². The superconducting transitions as measured by ??(T) at B=0 are found broad for both x=0.15 and 0.2 samples with transition widths ??2.5 and 6?K, respectively. The slope |dB _c2/dT| (where B _c2 is upper critical field) determined by resistive onsets, for the x=0.15 and 0.2 samples, has values ??7.5 and 3.5?T/K, respectively. The superconducting state characteristics as reflected by ??(T,B), M(T), magnetic J _c(B) and MMA response are typical of the presence of weakly linked inter-grain regions in both the samples. Our HRTEM images of the x=0.15 sample show the presence of high angle (??43^°) grain boundaries, which are well known to limit the J _c in cuprate-based high T _c bulk materials.     

Bulk modulus and hardness of chalcopyrite structured solids

The bulk modulus and microhardness can be represented by an empirical linear relation that is a simple function of melting temperature T_m, atomic volume Ω and product of ionic charges (Z₁Z₂Z₃). Values of bulk modulus B and microhardness H of A^IB^IIIC₂^VI and A^IIB^IVC₂^V chalcopyrite semiconductors exhibit a linear relationship when plotted against the k_BT_m/Ω (k_B = Boltzmann's constant), but fall on two straight lines according to the product of ionic charges of the compounds. This correlation is similar in form to other correlations in the literature for diffusion data of materials that indicate the significance of the melting temperature as a scaling or lattice dynamic properties of materials. The calculated results are compared with available experimental data and previous calculations based on phenomenological models.     

Disorder Tuned Superconductor Insulator Transition in La2−x (Sr/Ce) x CuO4 & NbN Superconducting Thin Films

In studying the magneto-resistivity ρ(B) in high pulsed magnetic fields up to 55 T, it is often observed that the ρ(B) curves for different temperatures in the vicinity of the critical temperature cross at the same field value, B=B _CP . We show how the crossing field changes as a function of the hole (or electron) doping x in La_2?x (Sr/Ce) _x CuO₄. The resistivity ρ and the magnetic field B at different temperatures may be scaled as R/R _CP and |B?B _CP|/T ^γ , respectively. This kind of scaling resulted in a conventional critical exponent γ=1/ν z=1.35 (ν z～0.74) in our La_2?x (Sr/Ce) _x CuO₄ thin films, and a much higher value of γ=4.35 (ν z～0.23) in the case of our disordered NbN films.     

Magnetic Transport Properties in GdBa2Cu3?x Ru x O7?δ Superconducting Phase

Bulk superconducting samples of type GdBa₂Cu_3?x Ru _x O_7?δ phase, Gd-123, with?x ranging from 0.0 to 0.15 were prepared by the conventional solid-state reaction technique. X-ray powder diffraction (XRD) and the electrical resistivity measurements were performed in order to investigate the effect of Ru⁴⁺ ions substitution on Gd-123 phase. Enhancement of the phase formation and the superconducting transition temperature T _c for GdBa₂Cu_3?x Ru _x O_7?δ phase up to x=0.05 was observed. The effect of magnetic field up to 4.4?kG on the electrical resistivity behavior of the prepared samples was studied to investigate the flux motion of this phase. The derived flux pinning energy?U, based on the thermally activated flux creep TAFC model, decreased with increasing the magnetic field?B. The flux pinning energy followed the exponent behavior as U(B)～B ^?β . The superconducting transition width ΔT increased as the magnetic field increased, showing the scaling relation as ΔT～B ⁿ . Using Ambegaokar and Halperin AH theory, the magnetic field and temperature dependence of U was found to be U(B,T)～ΔTB ^?η , η=β+n. The critical current density J _c (0) enhanced up to x=0.05, beyond which it decreased with further increase in Ru-content.     

Non-linear Flux Flow Resistance of Type-II Superconducting Films

We analyze the flux-flow (FF) regime in type-II superconducting films exhibiting quite strong pinning. By driving the vortex lattice (VL) up to high dissipative states, the moving VL undergoes an instability, leading to an abrupt change from the FF to the normal state, which is displayed in the current-voltage characteristics as a voltage jump at a critical vortex velocity v ^?. The temperature and magnetic field dependence of v ^? is investigated in different materials, and an unpredicted low field behavior of v ^?(B) is found. Moreover, for velocities lower than v ^?, a non-linear FF resistance is observed, with a ??peak?? in the current dependence of the dynamic resistance. This is a remarkable feature of a dynamic transition from disordered to ordered VL occurring in the FF state. We suggest that both unusual effects observed in v ^?(B) and R _FF(I) can be accounted for intrinsic pinning.     

Progress Toward Redetermining the Boltzmann Constant with a Fixed-Path-Length Cylindrical Resonator

A single, fixed-path-length cylindrical-cavity resonator was used to measure c ₀ = (307.825 2 ± 0.001 2) m · s^?1, the zero-density limit of the speed of sound in pure argon at the temperature of the triple point of water. Three even and three odd longitudinal modes were used in this measurement. Based on the ratio M/?? ₀ = (23.968 644 ± 0.000 033) g · mol^?1, determined from an impurity and isotopic analysis of the argon used in this measurement and the measured c ₀, the value k _B = 1.380 650 6 × 10^?23J · K^?1 was obtained for the Boltzmann constant. This value of k _B has a relative uncertainty u _r(k _B) = 7.9 × 10^?6 and is fractionally, (0.12 ± 8.1) × 10^?6 larger than the value recommended by CODATA in 2006. (The uncertainty is one standard uncertainty.) Several, comparatively large imperfections of our prototype cavity affect the even longitudinal modes more than the odd modes. The models for these imperfections are approximate, but they suggest that an improved cavity will significantly reduce the uncertainty of c ₀.     

Crystal structure of Rb3[UO2(CH3COO)3]2[UO2(CH3COO)(NCS)2(H2O)]

The structure of Rb₃[UO₂(CH₃COO)₃]₂[UO₂(CH₃COO)(NCS)₂(H₂O)] was studied by single crystal X-ray diffraction. The compound crystallizes in the monoclinic system with the unit cell parameters (at 100 K) a = 18.387(3), b = 16.398(3), c = 12.460(2) Å, β = 92.837(5)^°, V = 3752.4(11) ų, space group C2/c, Z = 4, R = 0.0390. The uranium-containing structural units of the crystals are isolated mononuclear groups [UO₂(CH₃COO)₃]^? and [UO₂(CH₃COO)(NCS)₂(H₂O)]^?, belonging to crystal-chemical groups AB ₃ ⁰¹ and AB⁰¹M ₃ ¹ (A = UO ₂ ²⁺ , B⁰¹ = CH₃COO^?, M¹ = NCS^? and H₂O) of uranyl complexes, respectively. The uranium-containing complexes are linked in a framework by hydrogen bonds and by electrostatic interactions with Rb⁺ cations.     

Abnormal Behavior of the Angular Dependence of Resistivity in?YBCO?Thin Films

Careful investigation of the angular dependence of resistivity ??(??) (?? is the angle between the magnetic field and the ab-planes) as a function of the temperature within the superconducting transition in an applied magnetic field B up to 1 T for a series of YBa₂Cu₃O_7??? (YBCO) thin films revealed a large variation in the shape and width of the minimum displayed in the vicinity of ??=0??, from a flat to a very sharp behavior. The series of films studied included both optimally doped and underdoped samples of different T _c , critical current density?J _c , film thickness, and preparation techniques. ??(??) measured for B close to ??=0?? (B parallel to ab-planes) for both B??J and B??J (J is the applied current density) showed two classes of samples; class of samples where ??(??) is independent of the direction of B relative to J and the other class where ??(??) depends on the orientation B relative to?J. This unusual unique behavior motivated us to investigate its origin by looking at the scaling of ??(??) as a function of the reduced field. Scaling of ??(??)) with the reduced field B(?? ^?2cos?² ??+sin?²)^1/2 allowed a quantitative determination of the value of ?? (intrinsic anisotropy) which varies between 7 and 400, and is independent of film thickness and J _c . Analysis of the microstructure though XRD of the films studied showed that the anisotropy is related to microstrain of the films.     

Synthesis and structure of Cs3[UO2(CH3COO)3]2(NCS)·H2O

The compound Cs₃[UO₂(CH₃COO)₃]₂(NCS)·H₂O (I) was synthesized and studied by IR spectroscopy and single crystal X-ray diffraction. Compound I crystallizes in the monoclinic system with the following unit cell parameters: a = 7.8286(9), b = 19.892(2), c = 20.050(2) Å, β = 94.527(2)°, space group P2₁/c, Z = 4, R = 0.0387. The uranium-containing structural units in crystals of I are mononuclear complexes [UO₂(CH₃COO)₃]^? belonging to crystal-chemical group AB ₃ ⁰¹ (A = UO ₂ ²⁺ , B⁰¹ = CH₃COO^?) of uranyl complexes.     

Constant-Volume Gas Thermometry with Different Helium-3 Gas Densities at NMIJ/AIST

Constant-volume gas thermometer (CVGT) measurements are conducted using ³He of three different densities as the working gas to obtain the thermodynamic temperature T _CVGT and the second virial coefficient of ³He, B, at temperatures down to 3 K, using the triple point of Ne as a reference temperature. Densities of 127 mol ?? m^?3 and 278 mol ?? m^?3 are used in addition to the density of 168 mol ?? m^?3 used in the measurement reported previously, where T _CVGT was obtained using the virial coefficient adopted by the International Temperature Scale of 1990 (ITS-90), B _ITS-90. T _CVGT is obtained by two methods, by the single- and multi-isotherm fitting of B to the three densities and by the method used in the previous work using one of the three densities and B _ITS-90. B obtained from the isotherm fitting agrees with B _ITS-90 within the uncertainty of the data used to derive B _ITS-90. Moreover, B obtained from a multi-isotherm fit agrees with that of recent theoretical ab initio calculations within 0.05?cm³ ?? mol^?1 at 5 K and above, and within 0.3?cm³ ?? mol^?1 down to 3 K. The values of T _CVGT obtained from the multi-isotherm fits assuming different forms for the temperature dependence of B agree with each other within 0.1?mK. T _CVGT obtained from the multi-isotherm fitting agrees with that obtained from the method in the previous report within 0.22?mK. The tendency of the difference between T _CVGT and the ITS-90 temperature reported in the previous work is confirmed in the present work.     

Effect of magnetic barrier on the plasma parameters in a Trimix-M galatea

The parameters of plasma trapped in a Trimix-M galatea with increased values of the magnetic barrier and the energy of a hydrogen plasma bunch injected in the trap have been determined. For a barrier magnetic field of B _b ～ 0.1 T, the plasma confinement time in the trap is τ_p ≈ 300 μs (which agrees with estimates obtained using formulas describing the classical transfer), the maximum electron density is n _e ～ 5 × 10¹³ cm^?3, and the electron and ion temperatures are T _e ≈ 20 eV and T _i ～ 2T _e, respectively. The energy of trapped plasma is ～110 J, and the ratio of the gaskinetic to magnetic pressure in the plasma is β₀ ～ 0.2.     

The Influence of Lithium Halides on the Superconducting Properties of YB2Cu3O7−x

The effects of addition to YBa₂Cu₃O_7?x of lithium halides (YBa₂Cu₃O_7?x (LiF) _y , and YBa₂Cu₃O_7?x (LiCl) _y ) on the structural, electric, magnetic, and transport properties are analyzed. Both structural and superconducting properties depend weakly on the lithium content up to y= 0.10. The critical temperature keeps on a value well above 91 K for a small amount of lithium halide (reaching 93.48K. for y= 0.02 in YBa₂Cu₃O_7?x (LiF) _y and 91.30 K in YBa₂Cu₃O_7?x (LiCl) _y ), but for higher concentration of Li it rapidly decreases (81.68K for y= 0.20). The same behavior is exhibited in the lower intragranular critical field. The intragranular critical current density depends on the magnetic field as a power law:j _c∝B ^?α, with a lithium-concentration-dependent α. The voltage–current characteristics follow a law typical for granular superconductors, V∝(I?I _c(B,T)) ^n(B,T). The dependence of the intergranular critical current, I _c, and of the exponent, n, on temperature, magnetic field, and concentration is analyzed.     

Antisymmetry of the logarithm of the compressibility factor z (ϱ) of real gases

We have considered analytic expressions, say z_exp, (_pT) of experimental values of the compressibility factor z ≡P/? RT of nitrogen, oxygen, ethane, propane, n-butane, n-pentane, ethylene, propylene, methane and xenon. In the high-density region ? ?[2?_c, 3.5?_a] we found that from about the critical temperature upwards, the isothermal dependence of Inz_exp(?, T) starts to exhibit a higher and higher degree of antisymmetry around a certain, slightly temperature dependent density, say ?_as(T). For the real gases considered this marked antisymmetric behaviour of Inz_exp(?, T) is mainly exhibited for densities higher than that of the experimental data represented by z_exp(?, T). In the case of N₂ gas in the high density region ? ?[2?_c, 3.4?_c] the experimental values of z(?, T) are availble for isotherms T ?[2.5T_c, 5.4T_c] and there In z_exp(?, T) would be completely antisymmetric around the density line ?_as = 2.7?_c were the values of z_exp(?, T) modified by only up to 0.3%, ie by a change of z_exp(?, T) comparable to the inaccuracy of experimental data and to their fit by z_exp(?, T). As a consequence, for N₂ gas the assumption that ?6² Inz(? = 2.7?_{c, T)Δ??² = 0} for all temperatures is not incompatible with the available experimental data.     

A single crystal X-ray diffraction study of Na4(UO2)4(i-C4H9COO)11(NO3)·3H2O

Synthesis and the results of IR and single crystal X-ray diffraction study of Na₄(UO₂)₄(i-C₄H₉COO)₁₁·(NO₃)·3H₂O are reported. The crystals are monoclinic; the unit cell parameters at 100 K are as follows: a = 13.697(2), b = 20.285(3), c = 15.991(3) Å, β = 103.760(3)°, space group P2₁, Z = 2, R = 0.0650. The uraniumcontaining structural units are mononuclear moieties [UO₂(i-C₄H₉COO)₃]^? and [UO₂(NO₃)(i-C₄H₉COO)₂]^?, belonging to crystal-chemical group AB ₃ ⁰¹ (A = UO ₂ ²⁺ , B⁰¹ = i-C₄H₉COO^? and NO ₃ ^? ) of uranyl complexes. The IR data are consistent with the results of the single crystal X-ray diffraction study. The influence of the carboxylate ligand volume on the structure of Na[UO₂L₃]·nH₂O crystals (L = acetate, n-butyrate, isovalerate ion) is analyzed.     

Elastic moduli and brittleness of diamondlike and zinc blende structured solids

In this paper, semiempirical formulae for both bulk modulus (B in GPa) and shear modulus (G in GPa) of diamondlike and zinc blende (A^NB^8−N) covalent solids are elaborated in terms of nearest neighbour distance (d in Å), covalent fraction (f_c) and product of ionic charges (Z_aZ_c) of the bonding. The resulting expressions can be applied to a broad selection of covalent materials and their modulus predictions are in good agreement with the experimental data and those from ab initio calculations. Furthermore, the correlation between the ratio G/B and the aforementioned bonding parameters was investigated. The analysis of this relationship demonstrates that compared to the nearest neighbour distance (d in Å), covalent fraction (f_c) and product of ionic charges (Z_aZ_c) are predominant parameters responsible for the brittle features of covalent materials.