Critical behaviour of electrical resistivity in 5 binary liquid systems

For five binary liquid systems CS₂+CH₃CN, CS₂+CH₃NO₂, CS₂+(CH₃CO)₂O, C₆H₁₂+(CH₃CO)₂O, n-C₇H₁₆+(CH₃CO)₂O, the electrical resistance has been measured near the critical solution temperatures. The behaviour is universal. Below T_c, the conductivities of the two phases follow ∣σ₁?σ₂∣～?^β, where ?=∣T?T_c∣T_c with β≈0.35. In the one phase region $\text{d}\text{R}\text{d}\text{T}\text{～?}{}^{\mathrm{-b}}$ with b≈0.35±0.1 and $\text{d}\text{R}\text{d}\text{T}$ is positive in some cases and negative in others.     

Magnetic correlation,excitation and slow dynamics in concentrated spin-glass alloys

Three kinds of neutron scattering experiments have been performed to clarify the role of magnetic clusters on the various properties of re-entrant spin-glasses. The presence of two kinds of spin-wave excitations, the limitations of magnetic phase diagrams and the mechanism of slow dynamics have been discussed based on the results of inelastic scattering, diffuse scattering and time-resolved small-angle scattering experiments, respectively.     

Field-induced magnetic transition in a Cu-Mn spin-glass alloy

The time-independent magnetization of a Cu-Mn alloy (9 at% Mn) as an isothermal function of field is found to describe an S-shaped curve indicative of a field-induced transition. The critical field for the transition decreases to zero as the temperature is raised to that of the susceptibility cusp.     

Quantum-mechanically induced asymmetry in the phase diagrams of spin-glass systems

The spin-1/2 quantum Heisenberg spin-glass system is studied in all spatial dimensions d by renormalization-group theory. Strongly asymmetric phase diagrams in temperature and antiferromagnetic bond probability p are obtained in dimensions d>or=3. The asymmetry at high temperatures approaching the pure ferromagnetic and antiferromagnetic systems disappears as d is increased. However, the asymmetry at low but finite temperatures remains in all dimensions, with the antiferromagnetic phase receding from the ferromagnetic phase. A finite-temperature second-order phase boundary directly between the ferromagnetic and antiferromagnetic phases occurs in d>or=6, resulting in a new multicritical point. In d=3, 4, 5, a paramagnetic phase reaching zero temperature intervenes asymmetrically between the ferromagnetic and reentrant antiferromagnetic phases. There is no spin-glass phase in any dimension.     

The soft X-ray spectra of concentrated binary alloys

The soft X-ray spectra of Al-Mg alloys are discussed within a simple model. Reasonable agreement with experiment is obtained. The results explain the main features of the spectra of any binary alloy with non-zero valence difference. Elementary consequences are discussed.     

NMR study of re-entrant spin-glass state in NiMn alloys

The temperature dependence of the average hyperfine field H̄_i and the nuclear spin-lattice relaxation time T₁ of ⁵⁵Mn on three different types (i = I, II and III) of Mn atoms in NiMn alloys containing 10 and 15 at % Mn have been measured. In 15 at % Mn alloy, H̄_III associated with Mn atoms having an antiparallel moment μ_III increases abruptly at 12K, while H̄_I and H̄_II associated with Mn atoms having parallel moments μ_I and μ_II do not with decreasing temperature. On the other hand T⁻¹₁ of ⁵⁵Mn of all three types of Mn atoms are largely enhanced at the same temperature, 12 K. This behavior was not observed in 10 at % Mn alloy.These effects observed in 15 at % Mn alloy are considered to be due to the freezing of the transverse component of the antiparallel moment μ_III due to the onset of the re-entrant spin-glass transition at 12 K.     

Silica based binary glass systems — refractive index behaviour and composition in optical fibres

Refractive index versus composition data are presented for three silica based binary glass systems SiO₂-B₂O₃, SiO₂-P₂O₅ and SiO₂-GeO₂. Using a near-field scanning method refractive index measurements were made on graded-index optical fibres, of known composition, fabricated by the chemical vapour deposition technique. The experimental data for each glass system is also compared with theoretical predictions of refractive index versus composition made from a single oscillator, Sellmeier model involving an oscillator energy and a dispersion energy term.     

Experimental study of the dynamic behaviour of non-azeotropic binary mixtures in heat pumps

The dynamic behaviour characteristics of some non-azeotropic refrigerant binary mixtures have been experimentally studied at various concentrations. The study was performed on a water/air heat pump during the heating mode under start-up conditions. The results presented in this study showed that the state of the non-azeotropic refrigerant mixture and its composition and concentration have a significant effect on the heat pump performance during start-up.In addition, the study demonstrated that non-azeotropic refrigerant mixtures could be potential CFC substitutes in heat pump applications.     

Signatures of spin-glass behaviour in PrIr2B2 and heavy fermion behaviour in PrIr2B2C

The magnetic and transport properties of PrIr(2)B(2) and PrIr(2)B(2)C have been investigated by dc and ac magnetic susceptibility, specific heat, electrical resistivity and magnetoresistance measurements. PrIr(2)B(2) forms in CaRh(2)B(2)-type orthorhombic crystal structure (space group Fddd). At low fields the dc magnetic susceptibility of PrIr(2)B(2) exhibits a sharp anomaly near 46 K which is followed by an abrupt increase below 10 K with a peak at 6 K, and split-up in ZFC and FC data below 46 K. In contrast, the specific heat exhibits only a broad Schottky type hump near 9 K which indicates that there is no long range magnetic order in this compound. The thermo-remanent magnetization is found to decay very slowly with a mean relaxation time τ = 3917 s. An ac magnetic susceptibility measurement also observes two sharp anomalies; the peak positions strongly depend on the frequency and shift towards high temperature with an increase in frequency, obeying the Vogel-Fulcher law as expected for a canonical spin-glass system. The two spin-glass transitions occur at freezing temperatures T(f1) = 36 K and T(f2) = 3.5 K with shifts in the freezing temperatures per decade of frequency δT(f1) = 0.044 and δT(f2) = 0.09. An analysis of the frequency dependence of the transition temperature with critical slowing down, τ(max)/τ(0) = [(T(f)-T(SG))/T(SG)](-zν), gives τ(0) = 10(-7) s and exponent zν = 8, and the Vogel-Fulcher law gives an activation energy of 84 K for T(f1) and 27.5 K for T(f2). While zν = 8 is typical for spin-glass system, the characteristic relaxation time τ(0) = 10(-7) s is very large and comparable to that of superspin-glass systems. An addition of C in PrIr(2)B(2) leads to PrIr(2)B(2)C which forms in LuNi(2)B(2)C-type tetragonal structure (space group I4/mmm) and remains paramagnetic down to 2 K. The specific heat data show a broad Schottky type anomaly, which could be fairly reproduced with CEF analysis which suggests that the ground state is a CEF-split singlet and the first excited state singlet is situated 15 K above the ground state. The Sommerfeld coefficient γ～300 mJ mol(-1) K(-2) of PrIr(2)B(2)C is very high and reflects a heavy fermion behaviour in this compound. We believe that the heavy fermion state in PrIr(2)B(2)C has its origin in low lying crystal field excitations as has been observed in PrRh(2)B(2)C.     

A Monte-Carlo study of meanders

We study the statistics of meanders, i.e. configurations of a road crossing a river through n bridges, and possibly winding around the source, as a toy model for compact folding of polymers. We introduce a Monte-Carlo method which allows us to simulate large meanders up to n=400. By performing large n extrapolations, we give asymptotic estimates of the connectivity per bridge R=3.5018(3), the configuration exponent , the winding exponent and other quantities describing the shape of meanders. Received 21 June 1999     

Unusual magnetic behaviour of Mn spin in magnetic PtFe alloys: Nuclear orientation study

The low temperature nuclear orientation of⁵⁴Mn in Pt₉₉Fe₁, Pt₉₉,₉Fe_0.1 and Pt₉₉,₉₅Fe_0.05 has been studied in the temperature rangé 5–60 mK and in the external magnetic field range 0–9 T. A considerable noncollinearity of Mn magnetic moments with respect to B_ext has been found even at rather high B_ext.     

A study on the electrochemical behaviour of polypyrrole films in concentrated aqueous alkali halide electrolytes

The electrochemical behaviour of polypyrrole films doped with dodecyl benzene sulfonate (PPy/DBS) in LiCl aqueous electrolytes has been investigated in order to find the electrolyte concentration suitable for the operation of PPy/DBS-based soft actuators. For this investigation, PPy/DBS films deposited on gold-coated quartz crystals by electropolymerization and simultaneous cyclic voltammetry and electrochemical quartz crystal microbalance techniques were used. During the first redox cycle, while large water movement is observed along with the counter ions in dilute electrolytes, such water transport in concentrated electrolytes is found to be very low. In dilute electrolytes, water molecules accompany counter ions as solvated molecules and due to osmotic effect. In concentrated electrolytes, water movement is less due to limited availability of free water as well as a smaller osmotic pressure difference. In highly concentrated aqueous electrolytes, the mass of the PPy/DBS film at the end of each redox cycle is found to drift, which can be controlled by changing the concentration of the electrolyte. The PPy/DBS films were also cycled at different scan rates in various alkali halide aqueous electrolytes of concentrations 0.1 and 1 M to determine the effective diffusion coefficients of alkali ions in the films. The effective diffusion coefficients were found to increase with the concentration of the electrolytes and decrease with the increase in size of cations.     

Corrosion behaviour of steel in concentrated phosphoric acid solutions

The corrosion rates of steel in concentrated phosphoric acid (1.0-11.0 M) were determined by the weight loss method, at three temperatures 298, 308 and 323 K. Results obtained show that corrosion rate increases with both acid concentration and temperature. The logarithm of corrosion rate was fitted against the acid concentration, values of Hammett H_o and Strehlow R_o(H) functions. The activation energies, enthalpies and entropies of the dissolution process were determined.     

Monte Carlo study on dynamical behaviour of spins and spin clusters in the 2D ± J Ising spin-glass

To investigate dynamical (time-dependent) behavior of spins and spin clusters in the two-dimensional ± J Ising spin-glass, we have evaluated the relaxation time τ_i of individual spins by the Monte Carlo simulation. An interesting finding is that, at least in the temperature range $\text{T ? 0.8J}$, most of τ_i are described by $\text{τ}{}_{\mathrm{i}}\text{∝}\text{exp}\text{{}\text{E}{}_{\mathrm{i}}\text{(T ? T}{}_0\text{}}$ with T₀?0.5J (E_i being a constant), which suggests that the system undergoes a glass transition obeying Fulcher's law.