Nanoscale physics

Short-range atomic and magnetic orders in substitution binary alloys and nanosize regions of corresponding orderings
Len E. G.1,2, Shatnii T. D.1, Lizunov V. V.1, Len T. S.3, Ushakov M. V.1
1 G.V. Kurdyumov Institute for Metal Physics, NAS of Ukraine, 36 Academician Vernadsky Blvd., UA-03142 Kyiv, Ukraine
E-mail: len@imp.kiev.ua
2 Kyiv Academic University, NAS and MES of Ukraine, 36 Academician Vernadsky Blvd., UA-03142 Kyiv, Ukraine
3 National Aviation University, 1 Kosmonavt Komarov Ave., UA-03058 Kyiv, Ukraine

Modern nanotechnologies require new materials, the properties of which change radically with relatively small external influences. The most promising from this point of view are systems with strong electron-electron correlations, in which with changes in temperature, external magnetic field, electron concentration and other external parameters the significant changes in the electronic structure are observed. They cause a wide range of phase transitions: between magnetic ordered and disordered or metal and dielectric states, to the superconducting state and to the modes of charge or spin transports.
Predicting the properties of such systems is inhibited due to the complexity of their theoretical description — it is common to describe only fully ordered or disordered systems. Only cluster methods for calculating the electronic structure allow us to partially advance in the sphere of incomplete magnetic and atomic orders. In this work, within the framework of the cluster expansion method for the one-particle Green's function and the single-band Hubbard model for alloys, the mutual influence of short atomic and magnetic orders and their joint influence on electronic and magnetic characteristics of systems with strong electron correlations are investigated as well as their exhibiting in extent of regions of corresponding orderings.
The substitution binary alloys АхВ1-х at x=0.5 and temperature of 0 K, at the same values of Coulomb repulsion potentials of electrons with opposite spins on one site for atoms of different types (U0=U0A=U0B) for the value of the impurity scattering potential W0=W0B–W0A=–0.2 is considered in the semi-elliptic model for the density of states. Energy is measured in units of half-width of the energy zone of a one-component crystal, and localized magnetic moments are measured in Bohr magneton mB. For the absence of a magnetic field, the probabilities of finding the projections of localized magnetic moments (m±) in the selected site are the same (P0m+=P0m-=0.5). Equilibrium values of magnetic moments and order parameters are found from the condition of free energy minimum. The parameters of short-range atomic and magnetic orders determine the sizes of regions of corresponding orderings in the investigated strongly correlated alloys.
As shown, the large domain with atomically ordered structure are suppressed for large range of alloys’ parameters due to influence of magnetic ordering, but the different nanosize regions with short-range stratification are predominated.