Theory of localized magnetic moments in metals I finite cluster approach

The origin of localized magnetic moments formation in metals is investigated theoretically using a self-consistent local spin density molecular cluster approach. Clusters with up to 55 atoms are employed to describe isolated impurity local moment behavior in the cases of Fe$\text{Ag}$ and Fe$\text{Pd}$. Densities of states and spin magnetic moments were determined and compared with results of spectroscopic (notably photoemission) and magnetization measurements, respectively. In the case of a noble metal host, the spin magnetization density is found to be highly localized around the Fe site; the iron moment is ≈ 3.9μ_B and the polarization of the host Ag atoms is small. In the case of a transition metal host, the iron moment is ≈ 3.2 μ_B but here the strong hybridization of the Fe-3d and Pd-4d states results in a large induced magnetic moment in the host PD metal — in essential agreement with experiment for this giant moment system.     

Soliton lattice to metal: A first order phase transition

$\text{In-situ}$ measurements of the electron spin resonance of [Na⁺_y (CH)^?y]_x during electrochemical doping are reported. The susceptibility and the esr linewidth exhibit step-like increases, with hysteresis, as functions of the chemical potential. These magnetic data, when combined with electrochemical and structural results on the same system, imply a first order phase transition from soliton lattice to metal.     

Melt growth and properties of B6P crystals

The compound semiconductor boron subphosphide has, at low temperatures, an ideal stoichiometry of 6 boron atoms to 1 phosphorus atom. This unit cell contains Bi₁₂P₂ and has a density of 2.60 $\text{g}\text{cm}{}^3$. It has been melted under inert gas pressure at 2120°C with very little loss of phosphorus. Data are presented on the diffusion coefficient of phosphorus, the refractive index, the band gap, and the optical absorption coefficient. Some optical data on B₆As are also given.     

The influence of Landau level broadening on temperature dependent cyclotron resonance linewidths in semiconductors

The effects of Landau level broadening, due to impurity fluctuations, on cyclotron resonance linewidths in semiconductors are reported. Allowing for level broadening, a calculation of the linewidth Γ shows a rapid low temperature increase, in contrast to earlier (non-broadening) calculations which give $\text{Γ ∞ T}{}^{\mathrm{<mtext>?</mtext><mtext>1</mtext><mtext>2</mtext>}}$. At low temperatures the broadening of the density of states causes a strong narrowing of the linewidth. These results are in good agreement with the experimental data reported for III-V and II-VI semiconductors. The effects of electron localisation are also considered.     

Semiconductor-metal transition in doped (CH)x: Thermoelectric power

Thermoelectric power studies of polyacetylene have been carried out as a function of dopant concentration and temperature. The thermopower of pure trans-(CH)_x is large $\text{(S =}\text{+850 μ V}\text{°K}\text{)}$ and positive consistent with p-type material. With iodine doping, (CHI_y)_x, the thermopower remains positive over the full range of concentration 0 < y < 0.22. The semiconductor-metal transition is clearly observed at n_c ? 3 mole %; S falls dramatically from $\text{S =}\text{+850 μ V}\text{°K}$ at y = 0.003 to $\text{S =}\text{+30 μ V}\text{°K}$ at y = 0.03. At higher concentrations, S remains nearly constant saturating at $\text{+18 μ V}\text{°K}$ in the heavily doped metallic polymer. Temperature dependences are consistent with metallic behavior at the highest dopant concentrations and hopping transport in the undoped and lightly doped polymer.     

Characterization of LiFeCl4 and AgFeCl4 ionic conductors

LiFeCl₄ and AgFeCl₄ are obtained by direct reaction between LiCl or AgCl and FeCl₃ at 300°C and 400°C respectively. Both compounds are monoclinic with $\text{a = 7.02 (1)}\text{A}\text{?}$, $\text{b = 6.33 (1)}\text{A}\text{?}$, $\text{c = 12.72 (4)}\text{A}\text{?}$, β = 92° (30') for LiFeCl₄ and $\text{a = 10.60 (5)}\text{A}\text{?}$, $\text{b = 6.30 (5)}\text{A}\text{?}$, $\text{c = 12.34 (10)}\text{A}\text{?}$, β = 106° (1) for AgFeCl₄.LiFeCl₄ is clearly isotypic of LiAlCl₄. Magnetic measurements characterize in both cases Fe³⁺ ions in a high spin tetrahedral situation. LiFeCl₄ becomes antiferromagnetic at low temperature (T_N?10 K). AgFeCl₄ reveals a more complex situation. On contrary to the silver derivative, LiFeCl₄ is a good ionic conductor with activation energy of 0.78 eV in the solid state below 105°C, and a sharp increase in the lithium mobility at this temperature.     

The influence of excess oxygen on the elastic properties of non-stoichiometric SrO crystals

Measurements have been carried out of the elastic constants of SrO in the virgin undoped state and of the changes produced in them by equilibrium doping with oxygen at ? 1200°C and oxygen partial pressure of 0.95 atm. The method used was Papadakis' pulse-echo overlap technique in conjunction with thermogravimetric analysis (T.G.A.) to determine mass and density changes due to oxygen doping.The values obtained for C₁₁, C₁₂ and C₄₄ of the virgin crystal at 23°C are

$\text{C}{}_{11}\text{= 17.60 ± 0.03 × 10}{}^{11}\text{dynes/cm}{}^2$

;

$\text{C}{}_{12}\text{= 4.808 ± 0.007 × 10}{}^{11}\text{dynes/cm}{}^2$

;

$\text{C}{}_{44}\text{= 5.577 ± 0.008 × 10}{}^{11}\text{dynes/cm}{}^2$

.(These values are in very good agreement with those of Son and Bartels [2].)Values for $\text{δC}{}_{11}\text{C}{}_{11}$ and $\text{δC}{}_{44}\text{C}{}_{44}$ were found to be ?1.74% and ?0.86% respectively. Accurate valu $\text{δC}{}_{12}\text{C}{}_{12}$ could not be obtained because of sample size limitations after quenching. However, C₁₂ was shown to definitely increase due to doping.Analysis of the results indicate that the elastic modulus changes can only be attributed to the formation of cation vacancies during doping. Analysis of the T.G.A. behavior indicates that this cation vacancy formation is probably associated with the presence of various tripositive cation and uninegative anion species depending upon the impurity concentrations of the sample. This implied impurity-controlled cation vacancy concentration is consistent with the earlier observed extrinsic nature of cation diffusion in SrO at 1200°C.     

Specific heat measurements in scandium-rare earth anisotropic spin glasses

We report on specific heat measurements at low temperature of the anisotropic spin glass alloys $\text{Sc}$Dy 3 at%, $\text{Sc}$Er 4.25 at% and $\text{Sc}$Er 10 at%. We find that at the lowest temperature range the data indicate the occurrence of an anisotropy induced gap around zero frequency in the density of states of the magnetic excitations. Moreover, some of our specific heat curves present a maximum coinciding with T_g, raising thus the question of thermal signs for a spin glass phase transition in anisotropic systems.     

Localized and nonlocalized impurity states in amorphous germanium

The purpose of this study was to investigate which impurities form localized states in amorphous Ge and to study the concentration dependence of the effect. The low temperature resistivity of amorphous alloy films deposited at 77°K was well fitted by the relation $\text{ρ = ρ}{}_{\mathrm{<mtext>0\; </mtext><mtext>exp</mtext>}}\text{[(}\text{T}{}_0\text{T}\text{)}{}^{\mathrm{<mtext>1</mtext><mtext>4</mtext>}}\text{]}$. The increase in the number of localized states resulting from an increase in the number of impurities is evidenced by a decrease in T₀ Impurities which lead to shallow energy levels in the crystalline form do not form localized states near the Fermi level while impurities with deep lying levels do.     

A combined LEED,AES and XPS study of the ZnO {0001} polar surfaces: I. LEED,AES and XPS of contaminated surfaces

The {0001} polar surfaces of ZnO single crystals have first been examined after a chemical treatment involving HCl and H₃PO₄ and a 24 hr bakeout at 250 °C. The impurities detected on the (000$\text{1}$)-O surface with AES were carbon, chlorine, phosphorus and to a lesser extent sulphur. On the (0001)-Zn surface, carbon, chlorine and sulphur were the dominant impurities, while the phosphorus signal was less important. These results were confirmed by XPS measurements on frehsly etched surfaces. The AES spectra were recorded as distribution curves N(E). Averaging, curve-fitting and related numerical techniques were used to obtain high resolution spectra, enabling the identification of the phosphorus L₁-transitions. The etched surfaces were cleaned progressively using argon ion bombardment and ohmic heating. It has been consistently observed that the clean surfaces exhibit primitive (1 × 1) structures. Superstructures such as $\text{(}\text{3}\text{×}\text{3}\text{)}$ on the (000$\text{1}$)-O surface, and $\text{(4}\text{3}\text{× 4}\text{3}\text{)}$ and (3 × 3) on the (0001)-Zn surface, were repeatedly observed at discrete spots of contaminated surfaces. A clear correlation with impurities as observed by AES however could not be found. Facetting was observed after prolonged heating.     

Spins and parities of low-lying states in 79Kr from the 78Kr(d,p)79Kr reaction

The structure of Kr has been investigated via the ⁷⁸Kr($\text{d}$, p)⁷⁹ Kr reaction using an isotopically enriched gas target and an 11.0 MeV vector-polarized deuteron beam. Differential cross sections, σ, and vector analyzing powers, A_y, have been measured from 25° to 95° for 10 proton groups below 2.5 MeV excitation energy. Comparisons of these distributions to DWBA calculations and empirical shapes were made to extract spectroscopic factors and values of spin and parity for these states.     

Spectroscopy of 41K by thermal neutron capture in 40K

The γ-ray spectrum emitted after thermal neutron capture in ⁴⁰K has been studied at the ILL high flux reactor with curved crystal Bragg, pair and Ge(Li) spectometers. 585 transitions were assigned to the reaction ⁴⁰K(n, γ)⁴¹K and 490 of them were placed into a ⁴¹K level scheme; 68 new states are proposed. On the basis of γ-ray branches to states with established spin and parity, many new spin-parity assignments were made. The level energies up to 4 MeV were measured with a precision of 8–50 eV relative to the 411.8 keV ¹⁹⁸Au standard, those above 4 MeV with a precision of 50–100 eV. The spin of the capture state was found to be $\text{I =}\text{7}\text{2}$; the neutron binding energy was determined to E_B = 10095.25(10) keV. The level density of $\text{I}{}^{\mathrm{\pi }}\text{=}\text{5}\text{2}{}^{\mathrm{\pm }}\text{,}\text{7}\text{2}{}^{\mathrm{\pm }}\text{,}\text{9}\text{2}{}^{\mathrm{\pm }}$ states was analyzed in terms of the constant-temperature Fermi gas model. It was shown that in this spin window the level scheme is almost complete up to an excitation energy of 5 MeV.     

Ultra high resolution of 6.2 keV 181Ta in 2H-TaSe2

The 6.2 keV γ-rays of ¹⁸¹Ta have been used to study the hyperfine interaction of ¹⁸¹Ta in the trigonal prismatic charge density wave material 2H-TaSe₂. Using a region of interest drive and an unstrained single crystal sample, we are able to resolve the splitting between the nuclear transition $\text{±}\text{5}\text{2}\text{→ ±}\text{3}\text{2}$ and $\text{±}\text{7}\text{2}\text{→ ±}\text{5}\text{2}$. Our experimental linewidth is that of the Ta metal.     

Thermopower of concentrated AuCr alloys

Measurements are presented of the thermopower of three concentrated $\text{Au}$Cr (0.9, 4.9 and 10.6 at.%Cr) alloys between 4 and 500°K. Considerable differences are observed in the thermopower compared with $\text{Au}$Fe alloys in a similar concentration range. Possible reasons for these differences are discussed in terms of current ideas on spin glasses and the pair model of Matho and Béal-Monod.     

Anomalous ionic conduction in AgBrAgI mixed crystals and multiphase systems

Ionic conductivity, σ, of the AgBrAgI system has been studied as a function of composition and temperature. The maximum conductivity of $\text{3 × 10}{}^{-4}\text{Ω}{}^{\mathrm{?1}}\text{cm}{}^{\mathrm{?1}}$ at 25°C is obtained for a AgI-20 mole% AgBr two-phase mixture which is $\text{\$}\text{?}$3 orders of magnitude larger than that predicted by the classical theories of Lord Rayleigh and Maxwell. On the other hand, the substitution of so-called homovalent ions, e.g. Br^? in AgI and I^? in AgBr one phase solid solutions leads to anomalously large increase in the ionic conductivity that cannot be explained in terms of the charge compensation (doping) mechanism, and is attributed to purely elastic displacements (lattice distortion) due to the very “wrong” size of the substituted ions. A quadratic dependence of conductivity on the concentration of substituents is substantiated. An important consequence of the latter anomaly is that AgBr + 30 mole% AgI exhibits σ $\text{\$}\text{?}$7 Ω^?1 cm^?1 at 380°C which is $\text{\$}\text{?}$170% higher than that of α-AgI, the best known superionic conductor, at its melting point (557°C).     

Hole centers in γ-irradiated,oxidized Al2O3

ESR observations of centers with $\text{S =}\text{1}\text{2}\text{, g ? 2, S = 1, g ? 2}$ have been made at 77 K on oxidized Al₂O₃ after γ-irradiation at 30°C. From the radiation growth data, it is shown that the $\text{S =}\text{1}\text{2}$ centers are precursors of the S = 1 centers. In addition, when the S = 1 centers anneal out at about 110°C, the $\text{S =}\text{1}\text{2}$ centers reappear and eventually anneal out at about 260°C. Previously Gamble and Cox, respectively, observed $\text{S =}\text{1}\text{2}$ and S = 1 paramagnetic centers in electron-irradiated nominally pure Al₂O₃ and γ-irradiated, oxidized, titanium-doped Al₂O₃. The models proposed for these centers were one hole and two holes trapped on oxygen ions adjacent to Al³⁺ vacancies. Our results further substantiate these models.     

Preparation and structural studies of lithium substituted nickel phosphorus trisulphide,Li2NiP2S6

Crystals of Li₂NiP₂S₆ may be prepared by direct combination of stoichiometric amounts of Li₂S, phosphorus, nickel and sulphur in a temperature gradient towards 750°C. The structure determined by X-ray powder diffraction is monoclinic C2/m with $\text{a = 5.926}\text{A}\text{?}\text{, b = 10.917}\text{A}\text{?}\text{, c = 6.718}\text{A}\text{?}\text{, β = 104.4°}$, and is based on the NiPS₃ layer structure with two Ni atoms substituted by lithium, and with two lithium atoms in the van der Waals gap.     

X-ray photoelectron spectra of iron complexes: Correlation of iron 2p satellite intensity with complex spin state

Metal and ligand core-level spectra have been obtained for 36 iron complexes which possess a variety of ligands including carbonyl, nitrosyl, triphenylphosphine,o-phenylenebis(dimethylarsine), halides and pseudohalides. Formal metal oxidation states range from ? 1 to + 3, and complex spin states represented in the series include 0, $\text{1}\text{2}$, $\text{3}\text{2}$, 2 and $\text{5}\text{2}$. A clear correlation between complex spin state and satellite intensity in the Fe 2p spectra is found. The satellite intensities observed experimentally are in approximate quantitative accord with those predicted by a “spin flipping” model. Although the present analysis does not provide a definitive choice between the “sudden approximation” and “spin flipping” models, the agreement between experimental satellite intensities and the intensities predicted by the “spin flipping” model suggests that such a mechanism can be important in the satellite process.     

Intrinsic and rotational states in 173Ta

High spin rotational levels in ¹⁷³Ta are populated in the ¹⁶⁵Ho(¹²C, 4n)¹⁷³Ta and ¹⁷⁵Lu(α, 6n)¹⁷³Ta reactions. The de-excitation γ-ray cascades are studied with Ge(Li) detectors. The rotational bands, which are built on the $\text{7}\text{2}$⁺(404), $\text{5}\text{2}$⁺(402), $\text{9}\text{2}$^?(514) and $\text{1}\text{2}$^?(541) intrinsic states, are identified up to high spin values. A state, interpreted as a three quasi-particle state with a probable spin of $\text{21}\text{2}$ is located at 1713 keV. Its half-life is about 100 ns. The behaviour of the moment of inertia of each rotational band versus the rotational frequency is compared with that of the doubly even core.     

Phenomenological constraints on broken supersymmetry

We show that the existence of massless color octet quarks, which appear in a class of broken supersymmetric field theories, implies the existence of additional light (? 1 GeV) unstable hadrons with large $\text{(? 10 μb)}$ production cross sections. We estimate the half-life for these states to be less than 10^?8 s. If it is greater than 10^°10 s, these states are already ruled out experimentally.