Disordered Transition Metal Alloys Research Articles

First-Principles Study on the Gilbert Damping Constants of Transition Metal Alloys, Fe–Ni and Fe–Pt Systems

We adapt the tight-binding linear muffin-tin orbital (TB-LMTO) method to the torque-correlation model for the Gilbert damping constant α and perform the first-principles calculation for disordered transition metal alloys, Fe–Ni and Fe–Pt systems, within the framework of the CPA. Quantitatively, the calculated α values are about one-half of the experimental values, whereas the variations in the Fermi level dependence of α are much larger than these discrepancies. As expected, we confirm in the (Fe–Ni) 1- X Pt X and FePt systems that Pt atoms certainly enhance α owing to their large spin–orbit coupling. For the disordered alloys, we find that α decreases with increasing chemical degree of order in a wide range.

Application of machine-learning methods to solid-state chemistry: ferromagnetism in transition metal alloys

Machine-learning methods are a collection of techniques for building predictive models from experimental data. The algorithms are problem-independent: the chemistry and physics of the problem being studied are contained in the descriptors used to represent the known data. The application of a variety of machine-learning methods to the prediction of ferromagnetism in ordered and disordered transition metal alloys is presented. Applying a decision tree algorithm to build a predictive model for ordered phases results in a model that is 100% accurate. The same algorithm achieves 99% accuracy when trained on a data set containing both ordered and disordered phases. Details of the descriptor sets for both applications are also presented.

Theoretical MXD-Investigations on Transition Metal Alloys Containing 4d-Elements

Results are presented on theoretical investigations on the magnetic X-ray dichroism (MXD) of disordered transition metal alloys containing 4d-elements. As found before from neutron scattering studies the induced moments of normally non-magnetic alloy components turned out to vary strongly from element to element and to depend on the magnetic alloy partner. This is reflected in the corresponding magnetic X-ray dichroism spectra that are in general found to be in very satisfying agreement with recent experimental results. In contrast to the interpretation of experimental spectra no fundamental difference could be found concerning the MXD at the L 2,3 -, M 2,3 - and N 2,3 -edges of 4d-elements.

A Tight-Binding-Bond Approach to Interatomic Forces in Disordered Transition Metal Alloys

ABSTRACTA tight-binding-bond approach to interatomic forces in disordered transition metal-Aluminium alloys is presented. The bond-order is calculated on a Bethe lattice reference system, well adapted to topologically disordered alloy. It is shown that the bond-order depends strongly on the strength of the pd hybridization in the AB alloy, leading to non additive potentials with a strong preference for the formation of pair of unlike atoms and short bond-distances in the A-B pairs. This is illustrated by studying the structural properties of liquid Al80Ni20 and Al80Mn20 alloys using molecular dynamics simulations and by comparing our results with the available experimental ones.

Use of CPA in recursion method for disordered transition metal alloys

The results of DOS calculations for the s-d valence band of disordered paramagnetic Cu0.50 Ni0.50 alloy by the recursion method are presentef for total and partial densities of states. Use of the CPA for the continued fraction termination has allowed to reveal the fine structure of the DOS in the band, which is due to non mean field features of the recursion method, also to reduce required computer time. Results for different sets of LCAO parameters, comparison of the DOS calculations with the experiment and other calculations results are presented.

Use of CPA in the Recursion Method for Disordered Transition Metal Alloys and Semiconductors

Use of CPA in the Recursion Method for Disordered Transition Metal Alloys and Semiconductors

Pseudogap formation and coexistence of localised and extended states in disordered transition metal alloys

The model of electron structure of Ti-based 3d metal alloys is proposed on the basis of the analysis of their electron properties. It includes the formation of the impurity d band almost non-hybridised with the conductivity electron states of Ti and the Mott-Hubbard transition in the former at some critical impurity concentration xc. It is shown that a pseudogap occurs in the conductivity band of the host near the Fermi energy as result of this transition. The experimental study of the concentration dependence of the conductivity sigma indicates the tendency of the host electron states to the Anderson localisation when x to xc which agrees with the conclusion of the model. At x>or approximately=xc the observed dependence of sigma on the temperature and magnetic field show the coexistence of extended and localised states near the Fermi level. The peculiarities of the physical properties of alloys with x approximately=xc and the nature of the anomalous magnetoresistance near the metal-insulator transition are discussed.

Electronic energy in transition metal alloying

The heats of formation of disordered transition metal alloys are related to the moments of the density of states within an analytical tight-binding model for the d band. We show that the values of the bandwidths of the elements and the difference between the energy levels are two important parameters in the evolution of the heats of formation of these alloys. These two major effects are discussed as functions of the average number of d electrons; their influence on the charge transfer, determined in a self-consistent way, is analysed.

The single-site approximation for disordered canonical d-band metal alloys

The LCAO theory of substitutionally disordered transition metal alloys, which allows to treat the different bandshapes and naturally leads to a matrix generalization of the concept of the multiplicative off-diagonal randomness, is developed within the single-site approximation. The novel expression for the full averaged resolvent is obtained, and applied to the evaluation of the density of states and the spectral density for the silver-palladium alloys. The results quantitatively agree with the recent KKR-CPA data.

Heats of formation of binary transition metal alloys

The heats of formation of disordered transition metal alloys are related to moments of the density of states within an analytical tight-binding model for the d band. The difference in bandwidth and in energy levels between the metals are two dominant effects on alloying. The d charge transfer is evaluated in a self consistent way from the knowledge of the partial densities of states.

The theory of strong coupling superconductivity in disordered transition metal alloys

The equations of strong coupling superconductivity in disordered transition metal alloys have been derived by means of “irreducible” Green's functions and on the basis of the alloy version of the Barisic-Labbe-Friedel model for electron-ion interaction. The configurational averaging has been performed by means of the coherent potential approximation. Making some approximations, we have obtained the formulas for the transition temperatureT c and the electron-phonon coupling constant λ. These depend on the alloy component and total densities of states, the phonon Green's function, and the parameters of the model.

Second‐order perturbation treatment of correlations in transition metal alloys

AbstractCorrelation effects in disordered transition metal alloys are studied within the degenerated Hubbard model using the perturbation theory limited to the second order in U/w (U Coulomb integral, w bandwidth). The influence of disorder is included within the coherent potential approximation. The theory is illustrated on a simple model of the copper–nickel alloy.

Electron—Phonon Interaction in Disordered Transition Metal Alloys

AbstractThe Hamiltonian of the electron‐phonon interaction is derived and applied to the description of disordered transition metal alloys. The coupled set of equations for the electron and phonon Green functions is derived with the help of the equation‐of‐motion technique. Neglecting the vertex corrections in the self‐energy operators the closed self‐consistent system of equations is obtained. The relevant configurational averaging is performed in the framework of the CPA. The electronic specific heat in the low‐temperature limit is calculated.

Electrical resistivity and glassy behaviour in crystalline metallic alloys

Positional disorder due to loss of translational symmetry is suggested as being responsible for most of the concentration dependence of the electrical resistivity of certain disordered transition metal alloys. It is then argued that in such cases the existence of tunneling states should be observable at low temperatures. Measurements of the thermal conductivity on Ti 0.67V 0.33 between 0.06 and 10 K confirm this conjecture.

The onset of ferromagnetism in transition metal alloys as a cooperative phase transition

It has been pointed out that the onset of ferromagnetism, as a function of concentration, in atomically disordered transition metal alloys is a cooperative magnetic phase transition which is unavoidably magnetically inhomogeneous. Here it is argued that the inhomogeneity of this phase transition should not invalidate the applicability of Landau's theory. Within the framework of this theory the concentration dependence of, and the effect of pressure on, the spontaneous magnetisation, initial susceptibility and the ferromagnetic Curie temperature are discussed.

Effects of order on the electronic structure of ferromagnetic transition metal alloys: application to FeCo and Ni3Fe

The electronic structures of ordered and disordered transition metal alloys are described in a tight-binding scheme. Charge transfer and magnetism are treated within a self-consistent Hartree-Fock model. The authors show that the rigid band splitting fails to take account of the ferromagnetism of these compounds. The densities of states of FeCo and Ni3Fe are found to be more sensitive to order than the ferromagnetic properties. Energetic calculations are performed giving an estimation of the ordering energy, and comparisons are made with experimental results.

Force–force correlation function approach to the electrical resistivity of disordered transition metal alloys

AbstractThe method of the force‐force correlation functions is used to derive, beyond the weak scattering approximation, a tractable approximative formula for the electrical resistivity of disordered binary alloys. The starting point is a one‐particle expression for the resistivity formulated in terms of the total scattering operator T. The local approximation is introduced by replacing the T operator by the atomic t matrices in order to treat transition metal alloys described by muffin‐tin single‐particle Hamiltonians. Short‐range multiple‐scattering corrections to the local approximation are evaluated using a non‐selfconsistent single‐site average‐t‐matrix approximation. Explicit results are given and discussed for the resistivity of a one‐dimensional muffin‐tin model for transition‐metal‐like alloys with resonant states.

Influence of electron correlation on the electrical resistivity of disordered transition metal alloys

physica status solidi (b)Volume 91, Issue 1 p. K39-K42 Short Note Influence of electron correlation on the electrical resistivity of disordered transition metal alloys K. Elk, K. Elk Wissenschaftsbereich Physik der Hochschule für Verkehrswesen Friedrich List, DresdenSearch for more papers by this authorJ. Richter, J. Richter Wissenschaftsbereich Physik der Hochschule für Verkehrswesen Friedrich List, DresdenSearch for more papers by this authorV. Christoph, V. Christoph Wissenschaftsbereich Physik der Hochschule für Verkehrswesen Friedrich List, DresdenSearch for more papers by this author K. Elk, K. Elk Wissenschaftsbereich Physik der Hochschule für Verkehrswesen Friedrich List, DresdenSearch for more papers by this authorJ. Richter, J. Richter Wissenschaftsbereich Physik der Hochschule für Verkehrswesen Friedrich List, DresdenSearch for more papers by this authorV. Christoph, V. Christoph Wissenschaftsbereich Physik der Hochschule für Verkehrswesen Friedrich List, DresdenSearch for more papers by this author First published: 1 January 1979 https://doi.org/10.1002/pssb.2220910154Citations: 1AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Citing Literature Volume91, Issue11 January 1979Pages K39-K42 RelatedInformation

Generalised perturbation theory in disordered transition metal alloys: application to the self-consistent calculation of ordering energies

The generalised perturbation method previously introduced for discussing ordering effects in transition metal alloys is extended to include charge transfer effects. A detailed numerical discussion of the validity of this method and of the role of charge transfers is given by using simple models for the electronic structure of the pure metals.

The Magnetic Properties of Disordered Transition Metal Alloys Using the Coherent Potential Approximation and Related Methods

For many years the properties of magnetic transition metal alloys were analyzed in terms of a rigid band model and the Stoner theory for magnetism in itinerant systems. Recently the introduction of the coherent potential approximation (CPA) has resulted in a description of the band structure of metallic alloys in terms of a local electronic charge density of states. The CPA and related approximations are derived in detail in this article and it is shown how these approximations have been extended to describe the properties of magnetic transition metal alloys in terms of local electronic spin densities. Both the statics and dynamics of itinerant magnetic alloys are discussed and the comparison with experiment is examined in detail. The article is concluded with a description of possible improvements to the CPA for magnetic alloys in particular for local environment effects.