Six low-strain zinc-blende half metals: Anab initioinvestigation

Abstract

A class of spintronic materials, the zinc-blende ͑ZB͒ half metals, has recently been synthesized in thin-film form. We apply all-electron and pseudopotential ab initio methods to investigate the electronic and structural properties of ZB Mn and Cr pnictides and carbides, and find six compounds to be half metallic at or near their respective equilibrium lattice constants, making them excellent candidates for growth at low strain. Based on these findings, we further propose substrates on which the growth may be accomplished with minimum strain. Our findings are supported by the recent successful synthesis of ZB CrAs on GaAs and ZB CrSb on GaSb, where our predicted equilibrium lattice constants are within 0.5% of the lattice constants of the substrates on which the growth was accomplished. We confirm previous theoretical results for ZB MnAs, but find ZB MnSb to be half metallic at its equilibrium lattice constant, whereas previous work has found it to be only nearly so. We report here two low-strain half metallic ZB compounds, CrP and MnC, and suggest appropriate substrates for each. Unlike the other five compounds, we predict ZB MnC to become/remain half metallic with compression rather than expansion, and to exhibit metallicity in the minority-rather than majority-spin channel. These fundamentally different properties of MnC can be connected to substantially greater p-d hybridization and d-d overlap, and correspondingly larger bonding-antibonding splitting and smaller exchange splitting. We examine the relative stability of each of the six ZB compounds against NiAs and MnP structures, and find stabilities for the compounds not yet grown comparable to those already grown.

Local field effects in half-metals: AGWstudy of zincblende CrAs, MnAs, and MnC

“…The lattice constant of the CrAs unit cell, 5.66Å, was determined by finding the lattice constant that minimizes the total energy within the initial PAW calculation while the lattice constants for MnAs (5.75Å) and MnC (5.08Å) were determined by finding lattice values that resulted in an integer magnetic moment. These results are in agreement with the previous study by Pask et al 11 and Qian et al 24 In addition, the exchange part of the self-energy matrix, Σ x , was constructed using wavefunctions with a cutoff of 430 eV of kinetic energy and the corresponding self-energy matrix used 2685 G vectors. We used the conventional GW approach, with a 181 G vector dielectric matrix for each spin channel, to handle the insulating case.…”

“…Pask et al 11 studied CrAs, along with MnAs, MnC and other ZB materials, using pseudopotential and LAPW calculations with a generalized gradient approximation (GGA) exchange-correlation functional 12 . GGA and local density approximation (LDA) functionals are, however, known to underestimate the semiconducting gap.…”

EPITAXIAL GROWTH OF CUBIC MnSb ON GaAs AND InGaAs(111)

“…3,4 The cubic polymorphs of many binary transition metal pnictides (TMPs), such as MnAs or CrSb, have been predicted to be half-metallic ferromagnetic (HMF) materials with Curie temperatures ðT C Þ well above room temperature which is essential if they are to be exploited in any functional device. [5][6][7] Many TMPs normally adopt a double hexagonal closepacked B8 1 niccolite structure (abbreviated n-), which has ABAC stacking along the c-axis (A = transition metal, B,C = pnictogen). The structure of the cubic (c-) TMP polymorphs are predicted to be signi¯cantly less energetically favorable than the n-polymorphs under normal growth conditions.…”

Nanospintronic properties of carbon-cobalt atomic chains

“…In (C n Co) ∞ chains the band gap and the net magnetic moment show interesting even-odd disparity depending on the number of carbon atoms in a unit cell. In contrast to those complications found in three-dimensional (3D) structures [8], half-metallicity of (C n Co) ∞ chains appear to be rather robust and straightforward. Moreover, the number of carbon atoms in a unit cell provides a structural parameter to engineer the electronic and magnetic properties of these atomic chains, such as their band gap and magnetic moment.…”