Coherent potential approximation

About: Coherent potential approximation is a research topic. Over the lifetime, 1930 publications have been published within this topic receiving 36805 citations.

Carrier-induced ferromagnetism in diluted local-moment systems

Abstract: The electronic and magnetic properties of concentrated and diluted ferromagnetic semiconductors are investigated by using the Kondo lattice model, which describes an interband exchange coupling between itinerant conduction electrons and localized magnetic moments. In our calculations, the electronic problem and the local magnetic problem are solved separately. For the electronic part an interpolating self-energy approach together with a coherent potential approximation (CPA) treatment of a dynamical alloy analogy is used to calculate temperature-dependent quasiparticle densities of states and the electronic self-energy of the diluted local-moment system. For constructing the magnetic phase diagram we use a modified Ruderman-Kittel-Kasuya-Yosida (RKKY) theory by mapping the interband exchange to an effective Heisenberg model. The exchange integrals appear as functionals of the diluted electronic self-energy being therefore temperature- and carrier-concentration-dependent and covering RKKY as well as double exchange behavior. The disorder of the localized moments in the effective Heisenberg model is solved by a generalized locator CPA approach. The main results are (1) extremely low carrier concentrations are sufficient to induce ferromagnetism; (2) the Curie temperature exhibits a strikingly nonmonotonic behavior as a function of carrier concentration with a distinct maximum; (3) ${T}_{C}$ curves break down at critical $n∕x$ due to antiferromagnetic correlations; and (4) the dilution always lowers ${T}_{C}$ but broadens the ferromagnetic region with respect to carrier concentration.

Magnetism and origin of non-monotonous concentration dependence of the bulk modulus in Fe-rich alloys with Si, Ge and Sn: a first-principles study

Abstract: Using the first-principles calculations based on the coherent potential approximation, we study the electronic structure, magnetic moments and the bulk modulus of FeX alloys with IVB group elements (X = Si,Ge,Sn) in the Fe-rich concentration range (x = 0.0?0.25), which form a stability region of bcc-related phases. In agreement with experiment, our calculations reproduce well a peculiar non-monotonous behaviour of the bulk modulus in Fe?Si alloys with increasing Si concentration. Such a dependence is found for all bcc-related disordered and partially ordered Fe?Si phases A2, B2 and D03, which is in contrast with an earlier suggestion that the non-monotonous bulk modulus behaviour is related to partial ordering in Fe?Si. In addition, our results predict a similar behaviour in Fe?Ge and Fe?Sn alloys. It is shown that the observed behaviour of the bulk modulus is entirely related to the changes of the magnetic properties with chemical composition.

Statistical physics of multicomponent alloys using KKR-CPA

Abstract: We apply variational principles from statistical physics and the Landau theory of phase transitions to multicomponent alloys using the multiple-scattering theory of Korringa-Kohn-Rostoker (KKR) and the coherent potential approximation (CPA). This theory is a multicomponent generalization of the S(2) theory of binary alloys developed by G. M. Stocks, J. B. Staunton, D. D. Johnson and others. It is highly relevant to the chemical phase stability of high-entropy alloys as it predicts the kind and size of finite-temperature chemical fluctuations. In doing so it includes effects of rearranging charge and other electronics due to changing site occupancies. When chemical fluctuations grow without bound an absolute instability occurs and a second-order order-disorder phase transition may be inferred. The S(2) theory is predicated on the fluctuation-dissipation theorem; thus we derive the linear response of the CPA medium to perturbations in site-dependent chemical potentials in great detail. The theory lends itself to a natural interpretation in terms of competing effects: entropy driving disorder and favorable pair interactions driving atomic ordering. Moreover, to further clarify interpretation we present results for representative ternary alloys CuAgAu, NiPdPt, RhPdAg, and CoNiCu within a frozen charge (or band-only) approximation. These results include the so-called Onsager mean field correction thatmore » extends the temperature range for which the theory is valid.« less

The Theory of Strong Coupling Superconductivity in Disordered Transition Metal Alloys

Abstract: 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.