The origins of phase stability in ordered and disordered Ni-Pt alloys

Using the atomic-sphere approximation formulation of the Korringa-Kohn-Rostoker coherent potential approximation (KKR CPA) method, we have studied the effects of relativity on the electronic structure of ordered and substitutionally disordered Ni-Pt alloys. The inclusion of mass-velocity and Darwin terms are found to be essential for describing the experimentally observed ground-state properties. For the stability of disordered Ni-Pt alloys we find that, in addition to relativity, the minimization of charge-transfer effects are important. We also find that the treatment of ordering tendencies based on the band energy term alone is not sufficiently accurate for alloys with charge-transfer effects. Further analysis, in terms of basis functions, densities of states and non-spherically averaged charge densities, indicate the importance ofs- andd-electrons of Pt for the stability of both ordered and disordered Ni-Pt alloys.     

Phonons and martensitic phase transitions in disordered Li−Mg alloys

We present a calculation of the phonon spectra and of the martensitic transition temperature for the bcc»hcp transformation in Li–Mg alloys. The treatment is based ona. pseudopotential-derived interatomic forces,b. a cluster relaxation technique for determining the static distortions of the mean crystal lattice in a substitutional alloy, andc. a recursion method for calculating the spectral functions and vibrational densities of state. We report that the observed variation of the martensitic temperature with concentration results from a delicate interplay of electronic and vibrational effects.This work was supported by the Jubiläumsfonds der Österreichischen Nationalbank under project no. 2141     

Magnetic relaxations in amorphous soft magnetic alloys

The paper reviews selected results of the extended experimental investigations of magnetic properties, time–temperature stability and workability of the soft magnetic amorphous alloys controlled by structural magnetic relaxation. Complex approach to the magnetic relaxations in multicomponent amorphous alloys is presented. The transition from magnetic after-effect to a new MAE spectrometry is illustrated on ternary amorphous CoSiB alloy.     

Landau levels in disordered alloys

The electronic structure of a substitutionally disordered alloy in a uniform magnetic field has been studied on a simple model of scattering potentials (zero range potentials). The coherent potential and single-site aproximation have been employed. It turned out that in wide energy region the Dingle temperature, characterizing the decay of the amplitude of de Haas — van Alphen oscillations, is determined by the part of self-energy which does not depend on magnetic field. The field dependent part is important only for a few Landau levels at the bottom of the band. The results can be applied to simple metals and semi-metals.     

Electronic topological transitions and phase stability in the fcc Al-Zn alloys

We report on a detailed investigation of the phase equilibria and the Fermi surface in the Al-Zn system. Our calculation are based on the density functional theory and we use the linear muffin-tin orbital method and the Green's function technique. The calculated free energies of alloy formation exhibit the existence of a miscibility gap between the alloys containing approximately 10 and 55 at.% of Zn, in agreement with the phase diagram of the Al-Zn system. Seven electronic topological transitions (ETT) were found in Al-Zn system within the stability range of the fcc solid solution. A relation between these ETT and the phase stability of the fcc Al-Zn solid solutions is established. We show that extremum points on the concentration dependencies of the thermodynamic properties of Al-Zn alloys can be explained by band-filling effects. Received 6 February 2002 Published online 19 November 2002     

Magnetooptical absorption in binary disordered alloys

The coherent potential approximation is used to compute the antisymmetric part (which depends linearly on the spin-orbital interaction) of the optical conductivity tensor of a disordered ferromagnetic alloy. The scattering of magnetized conduction electrons on the impurity potential of the alloy and on thermal vibrations of the lattice is considered.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 95–99, September, 1976.In conclusion we would like to express our deep gratitude to E. I. Kondorskii for posing the problem and for a number of valuable comments during discussions of the results.     

Pair effects in disordered ternary alloys

A generalization of the coherent potential approximation and its diagrammatic equivalent have been used to include pair effects in the electronic self-energy of compositionally disordered-model ternary alloys.     

Equilibrium vacancy concentration in disordered binary alloys

The equilibrium vacancy concentration in disordered binary alloy is calculated in this paper. The calculations are performed in the configuration approximation, explicitly taking into account various types of vacant site neighborhoods. The self-diffusion coefficient is determined as a function of alloy composition.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 79–83, May, 1972.     

Magnetism in FeNiW disordered alloys: Experiment and theory

We report here an experimental study of magnetization of FeNiW alloys at different compositions. We have studied variation of magnetization with temperature (at low external fields) and magnetic field (at low temperatures). The alloy shows para to ferromagnetic transitions across the composition range. We do not find any indication of the spin-glass phase. We have supplemented the experimental work with theoretical analysis using the first-principles tight-binding linear muffin-tin orbitals based augmented space recursion method. Our theoretical estimates of magnetic moment and Curie temperatures agree well with experiment. Our mean-field phase analysis also does not indicate the possibility of a spin-glass phase.     

On calculation of electronic states in disordered alloys

A new representation of the Green function for a disordered multicomponent substitution alloy is proposed, using which it is easy to separate one-, two-, etc. contributions to this Green function in corresponding equations. Due to this representation we succeed in obtaining common expressions for the configurationally averaged electron Green function with allowance for the electron scattering on clusters formed by an arbitrary number of atoms. The approach used is equally appropriate to described alloys both in the weak binding model, and in the tight binding one.     

Electrical resistivity in disordered,polycrsytalline FeNiTe alloys

Many disordered, crystalline and non-crystalline alloys and metallic conductors are characterized by positive as well as negative temperature coefficients of resistivity α(T) over a wide range of temperature. Experimental results are presented here to show the anomalous behaviour of resistivity with temperature in contrast to the existing theories. The anomalous electron properties can be understood in terms of an attractive interaction between conduction electrons and the localized excitations arising from structural deformity in the atomic arrangements. This scattering mechanism is used to explain the unusual departure from a linear temperature dependence above the Curie temperature (T_c) in Fe₂₈Ni₂₈Te₄₄, Fe₂₁Ni₂₂Te₅₇, Fe₁₆Ni₂₁Te₆₃ and Fe₈Ni₁₆Te₇₆ alloy.