Showing papers on "Coherent potential approximation published in 2008"
TL;DR: The ferrite only based scheme furnishes the fabricated NIM with magnetically tunable working frequency, less loss and the air-matched wave impedance.
Abstract: We demonstrated a construction of negative-index material (NIM) with epsilon(eff)=mu(eff)=-1 employing ferrites only, with no metallic components. Our design of the NIM is motivated by recent coherent potential approximation results and corroborated by exact numerical calculation demonstrating the negative refraction of an electromagnetic beam, with equal incident and refraction angles, as well as by the slab imaging phenomena, with the source-image separation twice as the slab thickness. The ferrite only based scheme furnishes the fabricated NIM with magnetically tunable working frequency, less loss and the air-matched wave impedance.
69 citations
TL;DR: In this article, the effect of phonons and disorder due to charged impurities and unitary scatterers on the infrared conductivity of graphene at finite chemical potential and temperature was studied.
Abstract: We study the infrared conductivity of graphene at finite chemical potential and temperature taking into account the effect of phonons and disorder due to charged impurities and unitary scatterers, that is, considering all possible single-particle scattering mechanisms. The screening of the long-range Coulomb potential is treated using the random phase approximation coupled to the coherent potential approximation. The effect of the electron-phonon coupling is studied in second-order perturbation theory. The theory has essentially one free parameter, namely, the number of charge impurities per carbon, nCi. Our most important results are the finding of an anomalous enhancement of the conductivity in a frequency region that is blocked by Pauli exclusion, in a picture based on independent electrons, and an impurity broadening of the conductivity threshold, close to twice the chemical potential. We also find that phonons induce Stokes and anti-Stokes lines that produce an excess conductivity, when compared to the far infrared value of σ0=(π/2)e2/h.
49 citations
TL;DR: In this paper, the structural properties of AgSbX2 (X=Se and Te) materials were investigated by X-ray diffraction and SEM microscopy, and the electrical conductivity, thermal conductivity and Seebeck coefficient have been measured as a function of temperature in the range from 300 to 600 k.
47 citations
TL;DR: In this article, the effect of phonons and disorder due to charged impurities and unitary scatterers on the infrared conductivity of graphene at finite chemical potential and temperature was studied.
Abstract: We study the infrared conductivity of graphene at finite chemical potential and temperature taking into account the effect of phonons and disorder due to charged impurities and unitary scatterers. The screening of the long-range Coulomb potential is treated using the random phase approximation coupled to the coherent potential approximation. The effect of the electron-phonon coupling is studied in second-order perturbation theory. The theory has essentially one free parameter, namely, the number of charge impurities per carbon, n^{{\rm C}}_i. We find an anomalous enhancement of the conductivity in a frequency region that is blocked by Pauli exclusion and an impurity broadening of the conductivity threshold. We also find that phonons induce Stokes and anti-Stokes lines that produce an excess conductivity, when compared to the far infrared value of \sigma_0 = (\pi/2) e^2/h.
41 citations
TL;DR: In this paper, the electronic structure and magnetic properties of disordered Fe-Pd alloys were investigated in the framework of density functional theory using the full potential local orbital method (FPLO).
Abstract: The electronic structure and magnetic properties of disordered Fe$_{x}$Pd$_{100-x}$ alloys $(50 < x < 85)$ are investigated in the framework of density functional theory using the full potential local orbital method (FPLO). Disorder is treated in the coherent potential approximation (CPA). Our calculations explain the experimental magnetization data. The origin of the tetragonal distortion in the Fe-Pd magnetic shape memory alloys is found to be a Jahn-Teller like effect which allows the system to reduce its band energy in a narrow composition range. Prospects for an optimization of the alloys' properties by adding third elements are discussed.
39 citations
TL;DR: In this paper, a variational method combined with a self-consistent procedure is adopted to discuss the binding energies of heavy-hole excitons in a strained wurtzite GaN/Al 0.7N quantum well by considering the hydrostatic pressure effect and screening due to the electron-hole gas.
Abstract: In the framework of effective mass and single-band approximations, a variational method combined with a self-consistent procedure is adopted to discuss the binding energies of heavy-hole excitons in a strained wurtzite GaN/Al0.3Ga0.7N quantum well by considering the hydrostatic pressure effect and screening due to the electron–hole gas. The built-in electric field in such a structure produced by spontaneous polarization and strain-induced piezoelectric polarization is considered in our calculation. A simplified coherent potential approximation is extended to calculate the energy gaps of the ternary mixed crystal AlxGa1−xN. The result indicates that the binding energies of excitons increase nearly linearly with pressure even when taking into consideration the modification of strain. It is also found that the percentage increase of the binding energy with pressure is influenced by the electron–hole density due to the influence of pressure on the screening and exclusion effects. The excitonic binding energies increase obviously with decreasing barrier thickness due to the built-in electric field.
36 citations
TL;DR: In this paper, the authors present an ab initio formalism for the calculation of transport properties in compositionally disordered systems within the framework of the Korringa-Kohn-Rostoker nonlocal coherent potential approximation.
Abstract: We present an ab initio formalism for the calculation of transport properties in compositionally disordered systems within the framework of the Korringa-Kohn-Rostoker nonlocal coherent potential approximation. Our formalism is based on the single-particle Kubo-Greenwood linear response and provides a natural means of incorporating the effects of short-range order upon the transport properties. We demonstrate the efficacy of the formalism by examining the effects of short-range order and clustering upon the transport properties of disordered AgPd and CuZn alloys.
29 citations
TL;DR: In this article, the electronic and magnetic properties of the quinternary full Heusler alloys of the type Co2[Cr1−xMnx][Al1−ySiy] employing three different approaches: (i) the coherent potential approximation; (ii) the virtual crystal approximation; and (iii) supercell calculations.
Abstract: We study the electronic and magnetic properties of the quinternary full Heusler alloys of the type Co2[Cr1−xMnx][Al1−ySiy] employing three different approaches: (i) the coherent potential approximation; (ii) the virtual crystal approximation; and (iii) supercell calculations. All three methods give similar results, and the local environment manifests itself only for small details of the density of states. All alloys under study are shown to be half-metals, and their total spin moments follow the so-called Slater–Pauling behavior of the ideal half-metallic systems. We especially concentrate on the properties related to the minority-spin band gap. We present the possibility to engineer the properties of these alloys by changing the relative concentrations of the low-valent transition metal and sp atoms in a continuous way. Our results show that for realistic applications, compounds rich in Si and Cr are ideal since they combine large energy gaps (around 0.6 eV), robust half-metallicity with respect to defec...
27 citations
TL;DR: In this paper, a theoretical approach based on a tight-binding model is developed for studying the effects of finite concentration gas adsorption (for what are known as diatomic, triatomic and quadratomic gas molecules in the general forms denoted by XY, XY2 and XY3, respectively) on electronic properties of armchair graphene nanoribbons.
Abstract: A theoretical approach based on a tight-binding model is developed for studying the effects of finite concentration gas adsorption (for what are known as diatomic, triatomic and quadratomic gas molecules in the general forms denoted by XY, XY2 and XY3, respectively) on electronic properties of armchair graphene nanoribbons (AGNRs). To consider the edge effects on electronic properties of pure AGNRs for the first time, two hopping parameters, for hydrogen–carbon and carbon–carbon nearest neighbor hopping, are considered. We found, for some specified values of hopping integrals and random on-site energies, that adsorbed molecule AGNRs act as donors or acceptors, which is consistent with reported experimental results for CO, NO2, O2, N2, CO2 and NH3 adsorption on graphene. Then by using these parameters and the coherent potential approximation, we investigated the effect of finite concentration gas molecule adsorption on the average density of states. Our results could be used to make p-type or n-type semiconductors by means of finite concentration adsorption of gas molecules or a gas sensor.
27 citations
TL;DR: In this paper, the electronic structure, magnetic moments, and ordering energies of highly magnetostrictive Fe1−xGax alloys from first-principles in the composition range up to x=0.25 were calculated.
Abstract: We calculate the electronic structure, magnetic moments, and ordering energies of highly magnetostrictive Fe1−xGax alloys from first-principles in the composition range up to x=0.25. The coherent potential approximation was used to treat effects of chemical disorder. Given an underlying bcc lattice in whole range compositions investigated, the DO3 type of ordering is found to have a lower energy than A2- and B2-type structures. We find that ordering energies strongly depend on the state of magnetic order such that thermal magnetic disorder strongly favors chemical ordering (DO3 and B2). The values of the magnetic moments of Fe on different sublattices of ordered structures are found to have a distinctive dependency on the Ga concentration. By taking into account the results of earlier fully relativistic and full potential calculations of magnetostriction for ordered stoichiometric Fe3Ga compounds and available experimental phenomenology, our results for disordered alloys suggest an eventually more complex...
26 citations
TL;DR: In this article, the thermodynamic quantities of high temperature metals and alloys using the statistical moment method, going beyond the quasi-harmonic approximations, are derived explicitly in closed analytic forms.
TL;DR: In this paper, the authors investigated the composition-dependent elastic properties and electronic structure of off-stoichionietric TiNi with a B2 structure by using the first-principles exact muffin-tin orbitals method in combination with coherent potential approximation and first-parameter plane-wave pseudopotential method (for computing bonding charge densities).
TL;DR: In this article, a new dilute magnetic semicoductors (DMS) other than II-VI and III-V semiconductor based DMS was proposed by the Korringa-Kohn-Rostoker method combined with the coherent potential approximation within the local spin density approximation and Monte Carlo simulations.
Abstract: In order to propose a new dilute magnetic semicoductors (DMS) other than II–VI and III–V semiconductor based DMS, magnetism of CuAlO2 based DMS is investigated by the Korringa–Kohn–Rostoker method combined with the coherent potential approximation within the local spin density approximation and Monte Carlo simulations (MCS). We found that effective exchange interactions (Jij) between magnetic ions are short-ranged and Jij's between magnetic ions in the same Cu-plane are ferromagnetic and ones between the different Cu-planes are nearly negligible in CuAlO2-based DMS. In comparison to this, Jij's between magnetic impurities occupied at Al-sites are slightly longer-ranged due to the stronger hybridization effect. According to MCS calculations, it is found that the value of the Curie temperature (TC) exceeds 80 K in (Cu,Fe)AlO2- and (Cu,Co)AlO2-DMS and that the TC is suppressed due to the strong percolation effect. This effect also appears in Cu(Al,TM)O2, where TM denote 3d-transition metal elements.
TL;DR: In this paper, high resolution experiments on the MnF2/ZnF2 system have shown that there is structure in the line shape of the excitations arising from the different excitation energies of Mn ions surrounded by different numbers of Zn neighbors.
Abstract: Measurements by neutron inelastic scattering techniques have provided detailed information about the magnetic excitations of substitutionally disordered antiferromagnets. In the dilute systems, such as MnF2/ZnF2, the excitations broaden and decrease in energy with increasing Zn concentration, while in mixed magnetic systems, such as KMnF3/KCoF3 there are usually two branches of the excitations which correspond to excitations propagating largely on one or other of the magnetic ions. Both of these results are in reasonable accord with the predictions of theories based on the coherent potential approximation and with the results of computer simulations. Recent high resolution experiments on the MnF2/ZnF2 system have shown that there is structure in the line shape of the excitations arising from the different excitation energies of Mn ions surrounded by different numbers of Zn neighbors.
TL;DR: In this article, a dynamical coherent potential approximation (CPA) to correlated electrons has been extended to a system with realistic Hamiltonian which consists of the first-principles tight-binding linear muffintin orbital (LMTO) bands and intraatomic Coulomb interactions.
Abstract: Dynamical coherent-potential approximation (CPA) to correlated electrons has been extended to a system with realistic Hamiltonian which consists of the first-principles tight-binding linear muffintin orbital (LMTO) bands and intraatomic Coulomb interactions. Thermodynamic potential and self-consistent equations for Green function are obtained on the basis of the functional integral method and the harmonic approximation which neglects the mode–mode couplings between the dynamical potentials with different frequency. Numerical calculations have been performed for Fe and Ni within the second-order dynamical corrections to the static approximation. The band narrowing of the quasiparticle states and the 6 eV satellite are obtained for Ni at finite temperatures. The theory leads to the Curie–Weiss law for both Fe and Ni. Calculated effective Bohr magneton numbers are 3.0 µ B for Fe and 1.2 µ B for Ni, explaining the experimental data. But calculated Curie temperatures are 2020 K for Fe and 1260 K for Ni, being ...
TL;DR: In this article, the authors reformulate the nonlocal coherentpotential approximation (NLCPA) as a unique and systematic theory and show that the previous formalism is a specific limiting case of the new formulation.
Abstract: The nonlocal coherent-potential approximation (NLCPA) has recently been introduced for describing short-range correlations in disordered systems, for example short-range ordering e ects in alloys. As a generalisation of the widely-used coherent-potential approximation (CPA), the NLCPA determines an e ective medium via the self-consistent embedding of a cluster with periodic Bornvon Karman boundary conditions imposed. Whilst this approach has the advantageous property of preserving the single-site translational invariance of the underlying lattice, it has recently been shown to yield spurious and non-unique results below some critical cluster size. In this paper we reformulate the NLCPA as a unique and systematic theory and show that the previous formalism is a specific limiting case of the new formulation. We explicitly demonstrate the theory for a one-dimensional tight-binding model in order to compare with exact numerical results.
Book•
17 Dec 2008
TL;DR: In this article, the authors proposed a relativistic local moment method (DLM) method for layered systems with spin-orbit interaction symmetry, based on the multiple scattering scheme.
Abstract: Introduction Preliminary Considerations Parallel, antiparallel, collinear, and noncollinear Characteristic volumina "Classical" spin vectors and spinors The famous spin-orbit interaction Symmetry Considerations Translational invariance Rotational invariance Colloquial or parent lattices Tensorial products of spin and configuration Cell-dependent potentials and exchange fields Magnetic configurations Green's Functions and Multiple Scattering Resolvents and Green's functions The Dyson equation Scaling transformations Integrated density of states Superposition of individual potentials The scattering path operator Angular momentum and partial wave representations Single particle Green's function Symmetry aspects Charge and magnetization densities Changing the orientation of the magnetization Screening transformations The embedded cluster method The Coherent Potential Approximation Configurational averages Restricted ensemble averages The coherent potential approximation The single-site coherent potential approximation Complex lattices and layered systems Remark with respect to systems nanostructured in two dimensions Calculating Magnetic Anisotropy Energies Total energies The magnetic force theorem Magnetic dipole-dipole interactions Exchange and Dzyaloshinskii-Moriya Interactions The free energy and its angular derivatives An intermezzo: classical spin Hamiltonians Relations to relativistic multiple scattering theory The Disordered Local Moment Method (DLM) The relativistic DLM method for layered systems Approximate DLM approaches Spin Dynamics The phenomenological Landau-Lifshitz-Gilbert equation The semiclassical Landau-Lifshitz equation Constrained density functional theory The semiclassical Landau-Lifshitz-Gilbert equation First principles spin dynamics for magnetic systems nanostructured in two dimensions The Multiple Scattering Scheme The quantum mechanical approach Methodological aspects in relation to magnetic anisotropies Physical properties related to magnetic anisotropies Nanostructured in One Dimension: Free and Capped Magnetic Surfaces Reorientation transitions Trilayers, interlayer exchange coupling Temperature dependence A short summary Nanostructured in One Dimension: Spin Valves Interdiffusion at the interfaces Spin valves and noncollinearity Switching energies and the phenomenological Landau-Lifshitz-Gilbert equation Heterojunctions Summary Nanostructured in Two Dimensions: Single Atoms, Finite Clusters, and Wires Finite clusters Finite wires and chains of magnetic atoms Aspects of noncollinearity Nanostructured in Two Dimensions: Nanocontacts, Local Alloys Quantum corrals Magnetic adatoms and surface states Nanocontacts Local alloys Summary A Mesoscopic Excursion: Domain Walls Theory of Electric and Magneto-Optical Properties Linear response theory Kubo equation for independent particles Electric transport-the static limit The Kubo-Greenwood equation Optical transport Electric Properties of Magnetic Nanostructured Matter The bulk anisotropic magnetoresistance (AMR) Current-in-plane (CIP) and the giant magnetoresistance (GMR) Current-perpendicular to the planes of atoms (CPP) Tunneling conditions Spin-valves Heterojunctions Systems nanostructured in two dimensions Domain wall resistivities Summary Magneto-Optical Properties of Magnetic Nanostructured Matter The macroscopic model The importance of the substrate The Kerr effect and interlayer exchange coupling The Kerr effect and magnetic anisotropy energy The Kerr effect in the case of repeated multilayers How surface sensitive is the Kerr effect? Summary Time Dependence Terra incognita Pump-probe experiments Pulsed electric fields Spin currents and torques Instantaneous resolvents and Green's functions Time-dependent multiple scattering Physical effects to be encountered Expectations Afterword Index
TL;DR: In this paper, the authors investigated the magnetic and half-metallic properties of Mn-doped p-type ZnO and the mechanism which controlled these properties using the Korringa-Kohn-Rostoker method combined with the coherent potential approximation (CPA).
TL;DR: In this paper, the optical properties of a single band model for (III,Mn)V diluted magnetic semiconductors (DMS) were studied, where the impurity spins were treated fully quantum mechanically in the coherent potential approximation (CPA).
Abstract: We study optical properties of a single band model for (III,Mn)V diluted magnetic semiconductors (DMS), treating the impurity spins fully quantum mechanically in the coherent potential approximation (CPA) Our CPA results show an interesting dependence of the optical conductivity on Kondo coupling, carrier density, nonmagnetic potential, and temperature We find that by taking into account the spin–flip effect, the calculated conductivity is in reasonable agreement with the ones obtained by Monte-Carlo simulations and experiments
Journal Article•
TL;DR: In this article, a dynamical coherent potential approximation (CPA) to correlated electrons has been extended to a system with realistic Hamiltonian which consists of the first-principles tight-binding linear muffintin orbital (LMTO) bands and intraatomic Coulomb interactions.
Abstract: Dynamical coherent-potential approximation (CPA) to correlated electrons has been extended to a system with realistic Hamiltonian which consists of the first-principles tight-binding linear muffintin orbital (LMTO) bands and intraatomic Coulomb interactions. Thermodynamic potential and self-consistent equations for Green function are obtained on the basis of the functional integral method and the harmonic approximation which neglects the mode–mode couplings between the dynamical potentials with different frequency. Numerical calculations have been performed for Fe and Ni within the second-order dynamical corrections to the static approximation. The band narrowing of the quasiparticle states and the 6 eV satellite are obtained for Ni at finite temperatures. The theory leads to the Curie–Weiss law for both Fe and Ni. Calculated effective Bohr magneton numbers are 3.0 µ B for Fe and 1.2 µ B for Ni, explaining the experimental data. But calculated Curie temperatures are 2020 K for Fe and 1260 K for Ni, being ...
TL;DR: In this paper, the electronic structure of Fe2�xV1+xAl upon changing the content x was theoretically investigated from first principles by using the fully relativistic Dirac linear-muffin-tin-orbital band structure method and the scalar-relativistic Korringa-Kohn- Rostoker method within the coherent potential approximation generalized to treat disorder in multicomponent complex alloys.
Abstract: Soft x-ray absorption spectra and their x-ray magnetic circular dichroism XMCD have been theoretically studied at the transition-metal L2,3 thresholds of the Heusler-type Fe2�xV1+xAl. The electronic structure of Fe2�xV1+xAl upon changing the content x was theoretically investigated from first principles by using the fully relativistic Dirac linear-muffin-tin-orbital band structure method and the scalar relativistic Korringa–Kohn– Rostoker method within the coherent potential approximation generalized to treat disorder in multicomponent complex alloys. Densities of valence states and spin and orbital magnetic moments are analyzed and discussed. The origin of the XMCD spectra in the Fe2�xV1+xAl compound is examined. The calculated results are compared to the experimental data. DOI: 10.1103/PhysRevB.77.134444
TL;DR: In this paper, a general expression relating the interlayer coupling energy to electronic density of states change due to interferences of electronic waves resulting from multiple reflections at disordered interfaces is derived.
Abstract: Multiple scattering theory of interlayer coupling in nanostructures with disordered alloylike interfaces is developed. Interface-localized potential responsible for the specular electron reflection from a perfect interface (potential step) is found in the framework of multiple scattering theory based on Green's functions approach. This allowed obtaining of a general expression relating the interlayer coupling energy to electronic density of states change due to interferences of electronic waves resulting from multiple reflections at disordered interfaces. In the case of a small spacer electron confinement (small scattering), the interlayer exchange coupling between two ferromagnets separated by a nonmagnetic spacer is found in the coherent potential approximation for electrons scattering at the disordered interfaces. The influence of disorder on the oscillating with a metallic spacer thickness exchange coupling is analyzed. The main effect is found to be a phase shift and amplitude change of these oscillations with the change of the parameters describing specular and diffuse spin-dependent electron scattering caused by the interfacial disorder.
TL;DR: In this article, the authors present a unified physical picture of wide band-gap II-VI and III-V DMS on the basis of the state-of-the-art ab initio electronic structure calculation done by using the Korringa-Kohn-Rostoker coherent potential approximation and local density approximation (KKR-CPA-LDA) to go beyond the LDA.
Abstract: Publisher Summary This chapter presents a unified physical picture of wide band-gap II–VI and III–V DMS—such as ZnO, ZnS, ZnSe, ZnTe, and GaN—on the basis of the state-of-the-art ab initio electronic structure calculation done by using the Korringa–Kohn–Rostoker coherent potential approximation and local density approximation (KKR–CPA–LDA) and the self-interaction corrected LDA (SIC-LDA) to go beyond the LDA. Zener's double-exchange interaction and superexchange interaction mechanisms are dominant in the magnetic magnetism. In the homogeneous system, the calculated Curie temperature (TC) obtained by using a Monte Carlo simulation (MCS) and electronic structure is in good agreement with the experiment (TC and photoemission spectroscopy [PES]). In the inhomogeneous system, the chapter presents a 3D Dairiseki phase and a 1D Konbu phase caused by spinodal nano-decomposition. A design of a growth position and shape-control method for nanomagnets in the superstructure by using self-organization is discussed. Finally, on the basis of the ferromagnetic (FM) mechanism of Zener's double-exchange mechanism, the chapter discusses a design of a new class of half-metallic ferromagnets without 3d transition metal (TM) impurities, such as C- or N-doped CaO, BaO, MgO, SrO, and SiO2.
TL;DR: In this paper, the authors describe proton and ionic conductors with lattice models and calculate the energy spectrum of the system in one-dimensional case, which consists of one or several energy bands depending on correlation strength.
Abstract: We describe proton and ionic conductors with lattice models. For proton conductors with hydrogen bonds we use the orientational-tunneling model that takes into account the proton transfer in the spirit of two-stage Grotthuss mechanism as well as the short-range interaction between protons. When simplified this model is reduced to the well-known spinless fermion model. In our investigation we focus on the role of short-range correlations between protons (ions) that may affect the behaviour of the system considerably. In frames of the projected coherent potential approximation we calculate the energy spectrum of the system in one-dimensional case. It consists of one or several energy bands depending on correlation strength. At half filling the system is in the insulating state when correlations are strong and is in the quasi-metallic state when correlations are weak. At certain range of parameters values we also observe the insulator-metal-like transition in the spectrum as it closes the gap with the temper...
TL;DR: In this paper, the results of ac susceptibility measurements of a (Mn065Co035)2P sample under pressure up to 75 GPa were obtained by using the Korringa-Kohn-Rostoker method incorporating the coherent potential approximation (KKR-CPA).
Abstract: In this paper we present the results of ac susceptibility measurements of a (Mn065Co035)2P sample under pressure up to 75 GPa The pressure induced low temperature ferromagnetic state in pressures above 5–6 GPa was established Theoretical analysis of the electronic band structure 'under pressure' was carried out by the Korringa–Kohn–Rostoker method incorporating the coherent potential approximation (KKR-CPA) We could conclude that the local magnetic moment decreases with pressure Moreover, when external pressure is applied along the c-axis, in the case of manganese atoms placed at the tetrahedral site, the magnetic moment practically disappears, but in the case of Co decreases only slightly This type of behavior may be responsible for the pressure induced phase transition from the antiferromagnetic (AF) state to the ferromagnetic (F) state KKR-CPA electronic band structure calculations undertaken in the antiferromagnetic state are also presented from which it was found that the density of states (DOS) at the Fermi level varies with applied pressure in the opposite way, when accounting for F and AF states The rapid decrease of DOS at EF in the ferromagnetic (Mn065Co035)2P additionally supports the experimentally observed pressure induced AF–F transition
TL;DR: In this paper, the standard model of Mn doping in GaAs is subjected to a coherent potential approximation (CPA) treatment, and the transport coefficients are evaluated within the linear response Kubo formalism.
Abstract: The standard model of Mn doping in GaAs is subjected to a coherent potential approximation (CPA) treatment. Transport coefficients are evaluated within the linear response Kubo formalism. Both normal and anomalous contributions to the Hall effect are examined. We use a simple model density of states to describe the undoped valence band. The CPA band structure evolves into a spin split band caused by the $p\text{\ensuremath{-}}d$ exchange scattering with Mn dopants. This gives rise to a strong magnetoresistance, which decreases sharply with temperature. The temperature $(T)$ dependence of the resistance is due to spin-disorder scattering (increasing with $T$), CPA band-structure renormalization, and charged impurity scattering (decreasing with $T$). The calculated transport coefficients are discussed in relation to the experiment, with a view of assessing the overall trends and deciding whether the model describes the right physics. This does indeed appear to be the case, bearing in mind that the hopping limit needs to be treated separately, as it cannot be described within the band CPA.
TL;DR: In this paper, the authors extended an effective medium approximation for the electronic structure of liquid metals and which is equivalent to the coherent potential approximation for alloys, to the problem of magnons in disordered ferromagnets.
Abstract: We have extended an effective medium approximation which was developed for the electronic structure of liquid metals and which is equivalent to the coherent potential approximation for alloys, to the problem of magnons in disordered ferromagnets The magnon self‐energy is obtained to first order in 1/?, where ? is an effective number of nearest neighbors, and the propagator is renormalized in a self consistent manner Comparisons are made with recent results on the diluted ferromagnet The theory is readily applied to alloys and amorphous materials
TL;DR: In this article, the influence of chemical disorder on the unoccupied electronic density of states by use of the ab-initio Coherent Potential Approximation method was investigated, along with corresponding spin-resolved Appearance Potential Spectroscopy measurements.
Abstract: The half-Heusler alloy NiMnSb is one of the local-moment ferromagnets with unique properties for future applications. Band structure calculations predict exclusively majority bands at the Fermi level, thus indicating {100%} spin polarization there. As one thinks about applications and the design of functional materials, the influence of chemical disorder in these materials must be considered. The magnetization, spin polarization, and electronic structure are expected to be sensitive to structural and stoichiometric changes. In this contribution, we report on an investigation of the spin-dependent electronic structure of NiMnSb. We studied the influence of chemical disorder on the unoccupied electronic density of states by use of the ab-initio Coherent Potential Approximation method. The theoretical analysis is discussed along with corresponding spin-resolved Appearance Potential Spectroscopy measurements. Our theoretical approach describes the spectra as the fully-relativistic self-convolution of the matrix-element weighted, orbitally resolved density of states.