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Spin-polarization and electronic properties of half-metallic Heusler alloys calculated from first-principles  [PDF]
I. Galanakis,Ph. Mavropoulos
Physics , 2006, DOI: 10.1088/0953-8984/19/31/315213
Abstract: Half-metallic Heusler alloys are amongst the most promising materials for future magnetoelectronic applications. We review some recent results on the electronic properties of these compounds. The origin of the gap in these half-metallic alloys and its connection to the magnetic properties are well understood. Changing the lattice parameter shifts slightly the Fermi level. Spin-orbit coupling induces states within the gap but the alloys keep a very high degree of spin-polarization at the Fermi level. Small degrees of doping and disorder as well as defects with low formation energy have little effect on the properties of the gap, while temperature effects can lead to a quick loss of half-metallicity. Finally we discuss two special issues; the case of quaternary Heusler alloys and the half-metallic ferrimagnets.
Charge Distributions in Metallic Alloys: a Charge Excess Functional theory approach  [PDF]
Ezio Bruno
Physics , 2002, DOI: 10.1103/PhysRevLett.91.166401
Abstract: Charge Distributions in Metallic Alloys: a Charge Excess Functional theory approach
Ferrimagnetism and antiferromagnetism in half-metallic Heusler alloys  [PDF]
I. Galanakis,K. Ozdogan,E. Sasioglu,B. Aktas
Physics , 2007, DOI: 10.1002/pssa.200776454
Abstract: Half-metallic Heusler alloys are among the most promising materials for future applications in spintronic devices. Although most Heusler alloys are ferromagnets, ferrimagnetic or antiferromagnetic (also called fully-compensated ferrimagnetic) alloys would be more desirable for applications due to the lower external fields. Ferrimagnetism can be either found in perfect Heusler compounds or achieved through the creation of defects in ferromagnetic Heusler alloys.
Weak crystallization theory of metallic alloys  [PDF]
Ivar Martin,Sarang Gopalakrishnan,Eugene A. Demler
Physics , 2015,
Abstract: We extend the Weak Crystallization theory to the case of metallic alloys. The additional ingredient -- itinerant electrons -- generates nontrivial dependence of free energy on the angles between ordering wave vectors of ionic density. That leads to stabilization of FCC, Rhombohedral, and icosahedral quasicrystalline (iQC) phases, which are absent in the generic theory with only local interactions. The condition for stability of iQC that we find, is consistent with the Hume-Rothery rules known empirically for majority of stable iQC; namely, the length of the primary Bragg peak wavevector is approximately equal to the diameter of the Fermi surface.
A New Paradigm for Metallic Alloys in Materials Science  [PDF]
Y. Ustinovshikov
Advances in Materials Physics and Chemistry (AMPC) , 2015, DOI: 10.4236/ampc.2015.57025
Abstract: In the article, taking into account the phase transition “ordering-phase separation” discovered in alloys, new concepts about the diffusion phase transformations in alloys are formulated: chemical interaction between dissimilar atoms exists always in all alloys and at any temperature of heating; alloys offer a surprising and not previously known property of changing the sign of the chemical interaction between dissimilar atoms at a change of the temperature or composition of alloys; diffusion processes occurring in alloys at different temperatures depend on the sign and the absolute magnitude of the energy of the chemical interaction between dissimilar atoms. All these three concepts are analyzed in detail, by the example of Ni-based and Co-based binary alloys using experimental results obtained by transmission electron microscopy. It is shown, on these ideas, how to carry out heat treatment of alloys more rationally, what principles should underpinned in the base of the construction of phase diagrams, how the microstructures of ordering and phase separation affect some properties of alloys.
Wise Computing: Towards Endowing System Development with True Wisdom  [PDF]
David Harel,Guy Katz,Rami Marelly,Assaf Marron
Computer Science , 2015,
Abstract: Encouraged by significant advances in algorithms and tools for verification and analysis, high level modeling and programming techniques, natural language programming, etc., we feel it is time for a major change in the way complex software and systems are developed. We present a vision that will shift the power balance between human engineers and the development and runtime environments. The idea is to endow the computer with human-like wisdom - not general wisdom, and not AI in the standard sense of the term - but wisdom geared towards classical system-building, which will be manifested, throughout development, in creativity and proactivity, and deep insights into the system's own structure and behavior, its overarching goals and rationale. Ideally, the computer will join the development team as an equal partner - knowledgeable, concerned, and responsibly active. We present a running demo of our initial efforts on the topic, illustrating on a small example what we feel is the feasibility of the ideas.
Misfit stabilized embedded nanoparticles in metallic alloys  [PDF]
Yu. N. Gornostyrev,M. I. Katsnelson
Physics , 2015, DOI: 10.1039/C5CP04641F
Abstract: Nanoscale inhomogeneities are typical for numerous metallic alloys and crucially important for their practical applications. At the same time, stabilization mechanisms of such a state are poorly understood. We present a general overview of the problem, together with a more detailed discussion of the prototype example, namely, Guinier-Preston zones in Al-based alloys. It is shown that coherent strain due to a misfit between inclusion and host crystal lattices plays a decisive role in the emergence of the inhomogeneous state. We suggest a model explaining formation of ultrathin plates (with the thickness of a few lattice constants) typical for Al-Cu alloys. Discreteness of the array of misfit dislocations and long-ranged elastic interactions between them are the key ingredients of the model. This opens a way to a general understanding of the nature of (meta)stable embedded nanoparticles in practically important systems.
Orbital magnetism in the half-metallic Heusler alloys  [PDF]
I. Galanakis
Physics , 2004, DOI: 10.1103/PhysRevB.71.012413
Abstract: Using the fully-relativistic screened Korringa-Kohn-Rostoker method I study the orbital magnetism in the half-metallic Heusler alloys. Orbital moments are almost completely quenched and they are negligible with respect to the spin moments. The change in the atomic-resolved orbital moments can be easily explained in terms of the spin-orbit strength and hybridization effects. Finally I discuss the orbital and spin moments derived from X-ray magnetic circular dichroism experiments.
An Environment-dependent Semi-Empirical Tight Binding Model Suitable for Electron Transport in Bulk Metals, Metal Alloys, Metallic Interfaces and Metallic Nanostructures I - Model and Validation  [PDF]
Ganesh Hegde,Michael Povolotskyi,Tillmann Kubis,Timothy Boykin,Gerhard Klimeck
Physics , 2013, DOI: 10.1063/1.4868977
Abstract: Semi-Empirical Tight Binding (TB) is known to be a scalable and accurate atomistic representation for electron transport for realistically extended nano-scaled semiconductor devices that might contain millions of atoms. In this paper an environment-aware and transferable TB model suitable for electronic structure and transport simulations in technologically relevant metals, metallic alloys, metal nanostructures and metallic interface systems is described. Part I of this paper describes the development and validation of the new TB model. The new model incorporates intra-atomic diagonal and off-diagonal elements for implicit self-consistency and greater transferability across bonding environments. The dependence of the on-site energies on strain has been obtained by appealing to the Moments Theorem that links closed electron paths in the system to energy moments of angular momentum resolved local density of states obtained ab-initio. The model matches self-consistent DFT electronic structure results for bulk FCC metals with and without strain, metallic alloys, metallic interfaces and metallic nanostructures with high accuracy and can be used in predictive electronic structure and transport problems in metallic systems at realistically extended length scales
Quantum transport in quasicrystals and complex metallic alloys  [PDF]
Didier Mayou,Guy Trambly De Laissardière
Physics , 2007,
Abstract: The semi-classical Bloch-Boltzmann theory is at the heart of our understanding of conduction in solids, ranging from metals to semi-conductors. Physical systems that are beyond the range of applicability of this theory are thus of fundamental interest. This is the case of disordered systems which present quantum interferences in the diffusive regime, i.e. Anderson localization effects. It appears that in quasicrystals and related complex metallic alloys another type of breakdown of the semi-classical Bloch-Boltzmann theory operates. This type of quantum transport is related to the specific propagation mode of electrons in these systems. We develop a theory of quantum transport that applies to a normal ballistic law but also to these specific diffusion laws. As we show phenomenological models based on this theory describe correctly the experimental transport properties. Ab-initio calculations performed on approximants confirm also the validity of this anomalous quantum diffusion scheme. Although the present chapter focuses on electrons in quasicrystals and complex metallic alloys, the concept that are developed here can be useful for phonons in these systems. There is also a deep analogy between the type of quantum transport described here and the conduction properties of other systems where charge carriers are also slow, such as some heavy fermions or polaronic systems.
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