Constitution and magnetic properties of Ni-Mn-Sn alloys - solid and liquid state

Ternary Ni₅₀Mn_50-xSn_x alloys have been studied by means of the magnetothermal analysis. The high temperature phase of the Ni₂MnSn Heusler alloy is obtained directly from the melt (structure of B2 type). From the paramagnetic behaviour of the Heusler alloy in the liquid as well as solid states, the same magneton number $\text{n′}{}_{\mathrm{<mtext>eff</mtext>}}\text{? 5}$ per Mn atom results. At lower temperatures this phase forms the L2₁ structure and shows a resulting ferromagnetic magneton number $\text{n}{}_{\mathrm{rmf}}\text{? 4}$, a value which is well known.     

Effects of composition on the upper critical field of V-Ga

Measurements of the temperature dependence of the upper critical field, H_c2(T), for a series of V_100?xGa_x materials are presented for 20.5 ≤ × ≤ 29.6. Fits of the data to conventional theory for a paramagnetically limited, dirty, type II superconductor show: 1) a maximum in T_c and H_c2(0) for x ? 25; 2) a constant ( for x ≤ 25; 3) a slowly increasing value of λ_so with increasing x up to x ～ 25; and 4) good agreement with stoichiometric ordered and thermally disordered V₃Ga. Above $\text{x ? 25}$ broader transitions are observed. For x = 25, T_c = 15.3 K, (, λ_so = 0.3 and H_c2(0) = 23.4 tesla. The effects of inclusion of strong-coupling in the theory are discussed briefly.     

Silver-compensated germanium center in α-quartz

A synthetic germanium-doped crystal of α-quartz was subjected to an electro-diffusion process $\text{ca. 600}\text{V}\text{cm}$, 625°K), in which Ag⁺ ions were introduced along the crystal's optic axis (c). A 9800MHz electron paramagnetic resonance spectrum at room temperature, taken after room temperature x-irradiation, revealed the presence of a silver-compensated germanium center A_Ge?Ag with large, almost isotropic ¹⁰⁷Ag and ¹⁰⁹Ag hyperfine splittings (26.078, 30.112 mT for magnetic field B∥c). Measurement of the spin-Hamiltonian (i.e. matrices $\text{g}$, $\text{A}{}^{73}{}_{\mathrm{<mtext>Ge</mtext>}}$, $\text{A}{}^{107}{}_{\mathrm{<mtext>Ag</mtext>}}$ and $\text{A}{}^{109}{}_{\mathrm{<mtext>Ag</mtext>}}\text{)}$ discloses that a suitable model for the observed center utilizes germanium, substituted for silicon, with the accompanying silver interstitial in a nearby c-axis channel, and with electronic structure in which an appreciable admixture Ge⁴⁺?Ag⁰ to Ge³⁺?Ag⁺ exists. Estimates of the unpaired electron orbital are presented.     

Magnetization and exchange constants in Zn1−xMnxSe

Magnetization of Zn_1?xMn_xSe ($\text{x}\text{≤ 0.1}$) was measured for magnetic field up to $\text{B}\text{= 15}\text{T}$ in the temperature range 2.2 – 30 K. The obtained data were described by Brillouin-like function. The direct comparison of magnetization data with the previous magnetooptical data enabled us to determine the s-d exchange constants in $\text{Zn}{}_{\mathrm{<mtext>1?</mtext><mtext>x</mtext>}}\text{Mn}{}_{\mathrm{x}}\text{Se}\text{:}\text{N}{}_{\mathrm{<mtext>o</mtext>}}\text{α = 0.26}\text{eV}$, $\text{N}{}_{\mathrm{<mtext>o</mtext>}}\text{β = ?1.31}\text{eV}$.     

Glass formation and vibrational properties in the (Ge,Sn) system

The glass forming tendency and infrared reflectance spectra are investigated in the (Ge, Sn) system. It is found that the glass formation of the SnSe system is much more difficult than that of the Ge system. This is mainly ascribed to the ionicity difference between GeSe and SnSe bonds. Infrared spectra in the glassy Ge_1-xSe_x system at the composition 0.67<x<1.0 indicate the presence of clusters within which the atomic connectivity is similar as in the glassy GeSe₂. The vibrational modes caused by the $\text{SnSe}{}_{\mathrm{<mtext>4</mtext><mtext>2</mtext>}}$ tetrahedron are found in the glassy (Ge, Sn)-Se system. It is suggested that tin atoms are mainly incorporated into the clusters. Importance of the medium range order is discussed in the formation of the glasses.     

Ni-Zr amorphous alloys: Low temperature specific heat and superconductivity

The specific heat (C_p) of the amorphous alloys Ni_100-xZr_x for x = 75, 65, 55 and 35 was measured from 0.8K to 40K and the composition trends of the transition temperature T_c, the enhanced density of states at the Fermi level N_γ(_F) and the Debye temperatures θ_D(0), θ_D(T) established. For the three superconducting compositions (x=75, 65, 55) N_γ(E_F increases rapidly with increasing [Zr] in agreement with the trend in amorphous Cu-Zr alloys. However, for the Zr-Ni alloys the bare density of states $\text{N}{}_0\text{(E}{}_{\mathrm{F}}\text{) =}\text{N}{}_{\mathrm{\gamma }}\text{(E}{}_{\mathrm{F}}\text{)}\text{(1 + λ}{}_{\mathrm{p}}\text{)}$ increases strongly with [Zr] in contrast to the Zr-Cu alloys where it is reported to be almost constant. We conclude that for the Ni-Zr alloys the electron-ion matrix element <I²> decreases with increasing [Zr]. Other results are related to recent photoemission studies of these alloys.     

The renormalization of the string operator in QCD

We shall observe that the renormalization of the string operator U(x₁, x₂; C) = Pexp{ig∫_x1^x2dx_μA^μ(x)} with an open path C (smooth and non-intersecting) is path-independently performed in any order of perturbation. To demonstrate this, the renormalization constants will be calculated up to order g⁴. Next the renormalization effect on the algebraic identity $\text{U(x}{}_1\text{, x}{}_2\text{;}\text{C}\text{)U(x}{}_2\text{, x}{}_3\text{;}\text{C}\text{) = U(x}{}_1\text{, x}{}_3\text{;}\text{C}\text{∪}\text{C}\text{)}$ will be discussed and it will be proved that the renormalization preserves the algebraic identity in any order of perturbation if the paths C and $\text{C}$ are smoothly connected at x₂. Finally, the string operator renormalization is extended to the case when the path C is smoothly closed (the Wilson loop operator). It is then shown that the renormalization factor which multiplicatively renormalizes the string operator in the case of the open path, is cancelled in any order of perturbation by the divergence appearing in the coincidence of the end points. As a results, the Wilson loop operator can be renormalized by the coupling constant renormalization alone.     

A model for phase transitions in Tetrathiafulvalene-Tetracyanoquinodimethane (TTF-TCNQ)

The observed phase transitions in Tetrathiafulvalene-Tetracyanoquinodimethane (TTF-TCNQ) are discussed using a simple model for the interchain coupling of charge density waves. Estimates based on Coulomb energies show that for 38 K < T < 49 K the components $\text{q}{}_{\mathrm{x}}\text{=}\text{π}\text{a}\text{+ q′}{}_{\mathrm{x}}$ and q_z of the wave vector associated with the charge density wave satisfy $\text{q}{}_{\mathrm{z}}\text{c}\text{q′}{}_{\mathrm{x}}\text{a?0.1}$, with $\text{q′}{}_{\mathrm{x}}\text{a～(T}{}_2\text{? T)}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ and T₂ = 49 K. A possible mechanism for the first order transition at 38 K is proposed. The results are compared with neutron and X-ray scattering and with isotope shifts of the transition temperatures.     

Spectroscopic information on ground-state Ar2, Kr2, and Xe2 from interatomic potentials

Calculations of vibrational and rotational level spacings of homonuclear inert gas diatomic molecules by numerical integration of the radial Schrödinger equation are presented. The potentials which were used for the ground states of Ar₂, Kr₂, and Xe₂ were obtained from accurate fits to the molecular beam scattering data. From the calculated $\text{Δ}\text{G}{}_{\mathrm{<mtext>v+</mtext><mtext>1</mtext><mtext>2</mtext>}}\text{'}\text{s}$ and B_v's, the following spectroscopic constants (in cm^?1) were fitted: for Ar₂ω_e = 31.92, ω_ex_e = 3.31, ω_ey_e = 0.11, B_e = 0.060, α_e = 0.004; for $\text{Kr}{}_2\text{ω}{}_{\mathrm{e}}\text{? 23.99}$, $\text{ω}{}_{\mathrm{e}}\text{x}{}_{\mathrm{e}}\text{? 1.30}$, $\text{ω}{}_{\mathrm{e}}\text{y}{}_{\mathrm{e}}\text{? 0.021}$, $\text{B}{}_{\mathrm{e}}\text{? 0.024}$, $\text{α}{}_{\mathrm{e}}\text{? 0.001}$; for $\text{Xe}{}_2\text{ω}{}_{\mathrm{e}}\text{? 21.26}$, $\text{ω}{}_{\mathrm{e}}\text{x}{}_{\mathrm{e}}\text{? 0.75}$, $\text{ω}{}_{\mathrm{e}}\text{y}{}_{\mathrm{e}}\text{? 0.008}$, $\text{B}{}_{\mathrm{e}}\text{? 0.013}$, $\text{α}{}_{\mathrm{e}}\text{? 0.0004}$.     

A thermodynamic study of nonstoichiometric cerium dioxide

Thermogravimetric measurements were performed on nonstoichiometric CeO_2?x in the temperature range 750–1500°C and from oxygen pressures of 10^?2 to 10^?26 atm. From this data the deviation from stoichiometry x = x(T, P_o2) was determined. The thermodynamic quantities Δ$\text{H}$_o2 and Δ$\text{S}$_o2 were calculated in the region 0.001? x ? 0.3 and found to be independent of temperature.In the composition region 0.001< x < 0.006, the variation of Δ$\text{S}$_o2 with x is consistent with a defect model involving randomly distributed doubly ionized oxygen vacancies. The experimental dependence of x and σ (electrical conductivity) is shown to be consistent with this model as Δ$\text{H}$_o2 (≈ -10 eV) exhibits a slight dependence on x. It is postulated that the variation in Δ$\text{H}$_o2 may result from lattice parameter increases with x, while the defects remain essentially randomly distributed.In the composition region 0.006 < x < 0.1, x ∝ with 1 < n < 5, and in the region 0.1 < x < 0.3, x ∝ with n increasing rapidly with x to n? 30. This behavior is believed to result from increasing defect interaction with increasing departures from stoichiometry. It is interesting to note that the ordered phase observed by Bevan and Kordis between CeO_1·72 and CeO_1·70 was not observed in this study at temperatures between 1300° and 1500°C.     

Predissociation and Λ-doubling in the even-parity Rydberg states of the nitrogen molecule

Predissociations in the y¹Π_g and $\text{x}{}^1\text{Σ}{}_{\mathrm{g}}{}^{\mathrm{?}}$ Rydberg states of N₂ (configurations $\text{1π}{}_{\mathrm{u}}{}^{\mathrm{?1}}\text{4pσ}$ and $\text{1π}{}_{\mathrm{u}}{}^{\mathrm{?1}}\text{3pπ}$, respectively) and their likely causes, are discussed. Peaking of rotational intensity at unusually low J values, without sharp breaking off, is interpreted as due to case c^? or case cⁱ predissociation. Λ doubling in the y state, attributed to interactions with the $\text{x}{}^1\text{Σ}{}_{\mathrm{g}}{}^{\mathrm{?}}$ state and with another, ¹Σ⁺, state of the same electron configuration as x, is analyzed. From this analysis the location of the (unobserved) ${}^1\text{Σ}{}_{\mathrm{g}}{}^{\mathrm{+}}$ state, here labeled x′, is obtained. It is concluded that the predissociation in the Π⁺ levels of the y state is an indirect one mediated by the interaction with x′ coupled with predissociation of x′ by a ${}^3\text{Σ}{}_{\mathrm{g}}{}^{\mathrm{?}}$ state dissociating to ${}^4\text{S +}{}^2\text{P}$ atoms: combined, however, with perturbation of the y state by the k¹Π_g Rydberg state (configuration $\text{3σ}{}_{\mathrm{g}}{}^{\mathrm{?1}}\text{4dπ}$), whose Π⁺ levels are completely predissociated.     

Local moment spin resonance in a Kondo system

The ESR of the system $\text{Yb:}\text{Au}{}_{\mathrm{x}}\text{Ag}{}_{\mathrm{1?x}}$ has been investigated for 0.7 ? x ? 1. The g-shift (Δg) and the temperature derivative of the linewidth $\text{(}\text{ΔH}\text{ΔT}\text{)}$ increase with decreasing Au concentration. For T ? 2°K effects in $\text{(}\text{ΔH}\text{ΔT}\text{)}$ are observed, which are attributed to the Kondo effect.     

On the asymptotic approximations of the solutions of a system of two non-linearly coupled harmonic oscillators

A procedure, closely related to the averaging method, is given for the construction of asymptotic approximations for the solutions of the Lagrangian system

$\text{d}\text{x}{}_1\text{d}\text{t}\text{=x}{}_2\text{,}\text{d}\text{x}{}_2\text{d}\text{t}\text{=?x}{}_1\text{+ε}\text{∑}\text{i, j=1}\text{4}\text{α}{}_{\mathrm{ij}}\text{x}{}_{\mathrm{i}}\text{x}{}_{\mathrm{j}}\text{,}\text{d}\text{x}{}_3\text{d}\text{t}\text{=x}{}_4\text{,}\text{d}\text{x}{}_4\text{d}\text{t}\text{=?4(1+δ)x}{}_3\text{+ε}\text{∑}\text{i, j=1}\text{4}\text{β}{}_{\mathrm{ij}}\text{x}{}_{\mathrm{i}}\text{x}{}_{\mathrm{j}}\text{, x}{}_1\text{(0)=a}{}_0\text{, x}{}_2\text{(0)=0, x}{}_3\text{(0)=b}{}_0\text{, x}{}_4\text{(0)=0,}$

where ε > 0 and δ > 0 are small parameters, a_ij = a_ji and β_ij = β_ji are real constants. The solutions can be represented as follows:

$\text{x}{}_1\text{=a}\text{cos}\text{(t+ξ), x}{}_2\text{=a}\text{sin}\text{(t+ξ), x}{}_3\text{=b}\text{cos}\text{(2t+ψ), x}{}_4\text{=2b}\text{sin}\text{(2t+ψ).}$

The asymptotic approximations (in a certain well-defined sense) of a, b, ξ and ψ are given. It is shown that a rapid variation of the phase, ψ(t), will take place if b → 0 for the case that δ ≈ ε or δ ? ε. In addition for the case δ ≈ ε the phenomenon of bifurcation will be discussed.     

Large p⊥ lepton production and the ψ(3100)

We determine the invariant cross section $\text{E}\text{d}\text{σ}\text{d}{}^3\text{p(s,x}{}_6\text{,pp}{}_{\mathrm{\perp }}\text{)}$ for pp→ψ(3100)+X near x₆=0 at NAL and ISR energies using the assumption that all large p_⊥ single leptons originate from the ψ. We adequately reproduce the single lepton data, and by suitable extrapolarion in x₆ ensure agreement with the NAL ψ production data (x₆?0.3). The magnitude of the resulting ψ production cross section is, however, roughly a factor of 3 larger than that observed by the recent CCRS-ISR experiment.     

Bounded diffusion in solid solution electrode powder compacts. Part II. The simultaneous measurement of the chemical diffusion coefficient and the thermodynamic factor in LixTiS2 and LixCoO2

Two electrochemical methods - involving the application of a long-time galvanostatic current pulse and a small potentiostatic voltage step to a M/M_xSSE cell - are presented. From the overvoltage, respectively current response the chemical diffusion coefficient ($\text{D}{}_{\mathrm{M}}{}^{\mathrm{+}}$) and the thermodynamic factor (? ln a/? ln c) are obtained. The methods have been applied to the cells: Li/1M·LiClO₄ in propylenecarbonate/Li_xTi_1.03S₂ 0.05 < x < 0.95, T = 20°C; and Li_xCoO₂ 0.10 < × < 1, T = 20°C. From the application of the current pulse/voltage decay method it followed: $\text{D}{}_{\mathrm{<mtext>Li</mtext>}}{}^{\mathrm{+}}\text{(}\text{Li}{}_{\mathrm{x}}\text{Ti}{}_{1.03}\text{S}{}_2\text{) = 1?4 × 10}{}^{\mathrm{?8}}\text{cm}{}^2\text{s}{}^{\mathrm{?1}}$, with a slight tendency to increase with decreasing x; $\text{D}{}_{\mathrm{<mtext>Li</mtext>}}\text{C}\text{(}\text{Li}{}_{\mathrm{x}}\text{CoO}{}_2\text{) = 2?40 × 10}{}^{\mathrm{?9}}\text{cm}{}^2\text{s}{}^{\mathrm{?1}}$, decreasing with decreasing x. These values are among the highest found for solid state Li⁺-ion diffusion, and will be closely evaluated and compared with data reported by other workers. The x-dependence of the thermodynamic factor, determined from kinetic data, for Li_xTi_1.03S₂ (x = 0.05-0.95) and Li_xCoO₂ (x = 0.60-1.00) is in accordance with a simple thermodynamic model. Unlike for Li_xTi_1.03S₂, the thermodynamic factor for Li_xCoO₂, determined from the EMF-x relation, cannot be accounted for by this model. Furthermore, a fast, but crude method to determine the average chemical diffusion coefficient in Li_xTi_1.03S₂ and Li_xCoO₂ is discussed.     

SIMS,AES, work function and flash desorption measurements of the CO adsorption on NiCu alloy surfaces

The chemisorption of CO on Cu, Ni and CuNi alloy surfaces was examined by SIMS, work function measurements and desorption spectroscopy. Using a dynamic SIMS technique the M⁺, M⁺₂, MCO⁺ and M₂CO⁺ emission at different temperatures (100–400 K) was measured as a function of CO exposure. In agreement with the work function and desorption experiments an increase of M⁺ and MCO⁺ emission due to the CO adsorption on Cu was found only at low temperatures (100–190 K). On the Ni surface an increase of Ni⁺, NiCO⁺ and Ni₂CO⁺ was measured up to 400 K. The adsorption of CO on CuNi alloy surfaces — as derived from the work function measurements — can be described by the assumption of two different states of adsorbed carbon monoxide. They can be characterized by different binding energies and from sign and magnitude different work function changes. These states were interpreted as adsorption at Ni or Cu sites of the alloy surfaces, respectively. To a certain extent the SIMS results from the alloy surfaces are incompatible with the work function measurements and desorption spectroscopy and the SIMS studies on the pure metals. A Cu⁺ emission with comparable intensity to the Ni⁺ emission was found for alloys with bulk concentrations of 60 and 40 at% Cu at 300 K. The ratio $\text{Ni}{}^{\mathrm{+}}\text{Cu}{}^{\mathrm{+}}$ was nearly independent of CO pressure and temperature. The measured ratios of $\text{Cu}{}^{\mathrm{+}}{}_2\text{(}\text{Cu}{}^{\mathrm{+}}\text{+}\text{Ni}{}^{\mathrm{+}}\text{)}$, $\text{Ni}{}^{\mathrm{+}}{}_2\text{(}\text{Cu}{}^{\mathrm{+}}\text{+}\text{Ni}{}^{\mathrm{+}}\text{)}$ and $\text{CuNi}{}^{\mathrm{+}}\text{(}\text{Cu}{}^{\mathrm{+}}\text{+}\text{Ni}{}^{\mathrm{+}}\text{)}$ with values about 10^?2 can be explained the basis of a statistical arrangement of Cu and Ni atoms in the alloy surface. The intensities of the MCO⁺ emissions are 10² times smaller than the corresponding values of the pure metals. No emission of M₂CO⁺ was found on CuNi during CO adsorption.     

Thermodynamical analysis of the EMC effect

Assuming that the sea quark distribution vanishes for x > 0.3, we analyse the F₂^Fe(x, Q²) and F₂^D(x, Q²) structure functions measured by the European Muon Collaboration in the framework of a thermodynamical model of the valence quarks. The experimental ratio $\text{F}{}_2{}^{\mathrm{<mtext>Fe</mtext>}}\text{(x)}\text{F}{}_2{}^{\mathrm{<mtext>D</mtext>}}\text{(x)}$ is well reproduced over the whole x range by the ratio of two valence quark distributions at different temperatures T and confinement volumes V. We obtain T_D?T_Fe≈3 MeV and $\text{V}{}_{\mathrm{<mtext>Fe</mtext>}}\text{V}{}_{\mathrm{<mtext>D</mtext>}}\text{≈ 1.3}$.