First-principles Dzyaloshinskii–Moriya interaction in a non-collinear framework

We have derived an expression of the Dzyaloshinskii–Moriya interaction (DMI), where all the three components of the DMI vector can be calculated independently, for a general, non-collinear magnetic configuration. The formalism is implemented in a real space—linear muffin-tin orbital—atomic sphere approximation (RS-LMTO-ASA) method. We have chosen the Cr triangular trimer on Au(111) and Mn triangular trimers on Ag(111) and Au(111) surfaces as numerical examples. The results show that the DMI (module and direction) is drastically different between collinear and non-collinear states. Based on the relation between the spin and charge currents flowing in the system and their coupling to the non-collinear magnetic configuration of the triangular trimer, we demonstrate that the DMI interaction can be significant, even in the absence of spin-orbit coupling. This is shown to emanate from the non-collinear magnetic structure, that can induce significant spin and charge currents even with spin-orbit coupling is ignored.

La3Ni4Al2: a new layered aluminide

The new ternary compound La3Ni4Al2 has been synthesized and the crystal structure has been studied by X-ray single crystal diffraction. La3Ni4Al2 is the first aluminide, crystallizing in the La3Ni4Ga2-type. The crystal structure of La3Ni4Al2 consists of La-layers and hetero-atomic Ni/Al layers, sequentially alternating along the a axis (pseudo-hexagonal c axis). According to electronic structure calculations using the tight-binding linear muffin-tin orbital method in the atomic-sphere approximation (TB-LMTO-ASA), strong Al–Ni interactions have been established. The coordination polyhedra for the Al atoms are cuboctahedra, whereas the bicapped square prism and bicapped square antiprism are typical for nickel atoms. The lanthanum atoms are enclosed in pseudo Frank–Kasper polyhedra.

First-principles Study of Electronic Properties of FeCrxSe Alloys

ABSTRACTWe performed first-principles study of electronic properties of FeCrxSe (x=0.0, 0.01, 0.02, 0.04) alloys using the Green’s function-based Korringa-Kohn-Rostoker Atomic Sphere Approximation method within the coherent potential approximation (KKR-ASA-CPA). The KKR-ASA-CPA method is implemented with density function theory (DFT). We find that the excess of Cr into FeSe significantly affects the electronic structure with respect to the parent FeSe. The results have been analyzed in terms of changes in the density of states (DOS), partial DOS, band structures, Fermi surface, bare Sommerfeld constant and the superconducting transition temperature of FeCr0.01Se, FeCr0.02Se and FeCr0.04Se alloys respectively. Our calculations show that calculated Tc for these alloys are close to experimental values, given the nature of approximations used in our calculations.

Study of Electronic and Magnetic Properties of CuPd, CuPt, Cu3Pd and Cu3Pt: Tight Binding Linear Muffin-Tin Orbitals Approach

Electronic structure of ordered alloys CuPd, CuPt, Cu3Pd and Cu3Pt have been studied using Tight Binding Linear Muffin-Tin Orbitals Atomic Sphere Approximation (TB-LMTO-ASA). For the electronic properties, we have performed band structure calculations. Our findings show that all the systems considered are metallic in nature. To know the contribution of the orbitals in the bands, the system is analyzed via fat bands which reveal most of the contributions on valence band for CuPd, CuPt, Cu3Pd and Cu3Pt is from d-orbital and on conduction band is from s and p-orbitals. We have also checked the magnetic properties of the alloys. The density of states for spin up and spin down electrons have found to be same in each and every steps, showing non-magnetic nature of CuPd, CuPt, Cu3Pd and Cu3Pt.Journal of Institute of Science and Technology, 2014, 19(1): 137-144

3-Dimensional Porosity in Electroless Ni-YSZ Composite Coating

The paper discussed on a 3-dimensional porosity network in electroless nickel (Ni) - yttria stabilized zirconia (YSZ) composite coating. The important characteristics of Ni-YSZ composite such as high ceramic YSZ incorporation and adequate porosity up to 40 vol.% are used as the main parameters. The arrangement of the porosity that give a 3-dimensional porosity network within the composite was design in Pro-Engineer Wildfire 3.0 software. Three structures of 3-dimensional porosity network were used namely honeycomb, atomic sphere and rhombic dodecahedra. The calculated area and volume of one unit porosity, consequently the number of porosity were compared between the three structures. These were supported by the porosity in the electroless Ni-YSZ composite coating obtained experimentally. Two batches were produced, EN-YSZ and EN-YSZ-G representing samples without and with pore former respectively. The two batch samples were investigated and compared. The addition of graphite pore former was burnt out completely and left porosity in the coating.

Ab-initio studies of thermal and superconducting properties of HfX2 alloys (X = Tc, Re, and Os)

A systematic study of thermal properties such as the Debye temperature, specific heat coefficient, Grüneisen constant, electron-phonon coupling constant and transition temperature have been carried out using the results of electronic band structure and related characteristics, for hafnium superconducting alloys, namely, HfTc2, HfRe2 and HfOs2. Computation of the electronic band structure and associated properties has been carried out using the tight-binding-linear-muffin-tin-orbital (TBLMTO) method within atomic sphere approximation (ASA). The calculated values have been compared with the available results of literature data.

Tuning of Energy Band Gaps in Ternary Semiconductors

The first principle investigations on electronic structure of ABC2 (A = Cd; B = Si, Ge, Sn; C= P, As) pnictides using the Tight Binding Linear Muffin Tin Orbital (TB-LMTO) method within the Atomic Sphere Approximation (ASA) is reported. Variation of Eg with pressure reveals the direct and pseudodirect natures of these compounds. CdSiP2 shows a pseudo direct and CdGeP2, CdSnP2, CdSiAs2, CdGeAs2 and CdSnAs2 show direct band gap natures. Semiconductor to metal transition at high pressures is observed. Metallisation volumes (V/Vo) m and pressures (Pm), bulk modulus (Bo) and its pressure derivative (Bo 1) are reported. Correlation connecting Bo and the unit cell volume (Vo) is established.