An ab-initio theoretical investigation of the soft-magnetic properties of permalloys

We study Ni80Fe20-based permalloys with the relativistic spin-polarized Korringa-Kohn-Rostoker electronic structure method. Treating the compositional disorder with the coherent potential approximation, we investigate how the magnetocrystalline anisotropy, K, and magnetostriction, lambda, of Ni-rich Ni-Fe alloys vary with the addition of small amounts of non-magnetic transition metals, Cu and Mo. From our calculations we follow the trends in K and lambda and find the compositions of Ni-Fe-Cu and Ni-Fe-Mo where both are near zero. These high permeability compositions of Ni-Fe-Cu and Ni-Fe-Mo match well with those discovered experimentally. We monitor the connection of the magnetic anisotropy with the number of minority spin electrons, Nmin. By raising Nmin via artificially increasing the band-filling of Ni80Fe20, we are able to reproduce the key features that underpin the magnetic softening we find in the ternary alloys. The effect of band-filling on the dependence of magnetocrystalline anisotropy on atomic short-range order in Ni80Fe20 is also studied. Our calculations, based on a static concentration wave theory, indicate that the susceptibility of the high permeability of the Ni-Fe-Cu and Ni-Fe-Mo alloys to their annealing conditions is also strongly dependent on the alloys' compositions. An ideal soft magnet appears from these calculations.Comment: 20 pages, 6 figure

Calculation of the P-T phase diagram and tendency toward decomposition in equiatomic TiZr alloy

Electronic, structural and thermodynamic properties of the equiatomic alloy TiZr are calculated within the electron density functional theory and the Debye-Gruneisen model. The calculated values of the lattice parameters a and c/a agree well with the experimental data for the alpha, omega and beta phases. The omega phase is shown to be stable at atmospheric pressure and low temperatures; it remains energetically preferable up to T=600K. The alpha phase of the TiZr alloy becomes stable in the range 600K<T<900K, and the beta phase at temperatures above 900K. The constructed phase diagram qualitatively agrees with the experimental data available. The tendency toward decomposition in the equiatomic alloy omega-TiZr is studied. It is shown that in the ground state the omega phase of the ordered equiatomic alloy TiZr has a tendency toward ordering, rather than decomposition.Comment: 6 pages, 8 figure

Coherent lidars based on intracavity heterodyning of echo signals

The development and technical realization of the method of laser sounding of the atmosphere based on the effects of mixing of reference and external fields of scattering inside a laser cavity are presented. An approximate theory of the method was developed on the basis of the investigations using the model of a three-mirror laser. The nonlinear effect of a wideband laser on frequency-dependent external influences of the atmosphere was investigated. The field measurements of gaseous composition of the atmosphere were performed on the basis of a given method of coherent reception using a tunable CO2 laser

Formation and tuning of 2D electron gas in perovskite heterostructures

Oxide interfaces provide very intriguing phenomena, in particular a 2D electron gas (2DEG) emerging between robustly insulating perovskites. The 2DEG was detected in 2004 beneath polar LaAlO3 (LAO) epitaxially grown on TiO2-terminated SrTiO3 (001) (STO). Herein, recent first-principles studies of 2DEGs are reviewed. Using a Green function method, the family of the polar/nonpolar (001) interfaces: LAO/STO, LaFeO3/STO, and STO/KTaO3 is computed. In the context of 2DEG, one of two insulating perovskites, at least, must be polar. The effect of a polar/polar interface is modeled for LAO/KTaO3(001) and also for the (110) and (111) interfaces of LAO/STO. Starting from the defectless superlattice with its two differently terminated interfaces, we demonstrate that the 2DEG and 2D hole gas appear there, respectively, due to the presence of excessive electrons or holes. 2DEG is evaluated by its layer-resolved density profile along [001], as well as the Fermi surface cross sections and effective masses, which are directly related to the transport properties. The effects of intermixed cations, their vacancies, and oxygen vacancies at each interface of LAO/STO are calculated. Finally, we show how to tune reversibly the 2DEG by changing the electronic balance at the LAO surface that mimics the effect of ionic liquid gating