Band gap and magnetism engineering in Dirac half-metallic Na₂C nanosheet via layer thickness, strain and point defects

authored by

A. Bafekry, Bohayra Mortazavi, S. Farjami Shayesteh

Abstract

Na₂C is a novel two-dimensional material with Dirac Half-metal (DHM) characteristic, exhibiting a combination of single-spin massless Dirac fermions and half-semimetal. In this paper based on the first-principles calculations, we studied the mechanical, electronic, magnetic and optical properties of Na₂C nanosheet. The elastic modulus of Na₂C was measured to 18.5 N/m and isotropic, whereas it shows anisotropic tensile strengths of 2.85 and 2.04 N/m, for the loading along the zigzag and armchair directions, respectively. We found that Na₂C, is a DHM with band gap of 0.7 eV in the up-spin channel and has 2 μ_B magnetic moment per unit cell. In addition, we investigated the effects of number of atomic layers (thickness), electric field and strain on the possibility of further tuning of the electronic and magnetic properties of Na₂C. Our calculations show that by increasing the number of layers from monolayer to bulk, a transition from DHM to ferromagnetic metal occurs with a high magnetic moments in the range of 16–30 μ_B. With applying an electric field on the Na₂C bilayer (within the ferromagnetic and anti-ferromagnetic orders), energy band gap is slightly increased. In addition our results indicate that the electronic structure can be significantly modified by applying the mechanical straining. In this regard, under the biaxial strain (from 0% to −8%) or large uniaxial strains (>-6%), we observed the DHM to ferromagnetic-metal transition. Moreover, vacancy defects and atom substitutions can also effect the electronic and magnetic properties of Na₂C nanosheet. Defective Na₂C with single and double vacancies, was found to show the metallic response. With various atom substitutions this nanosheet exhibits; ferromagnetic-metal (Si and Be) with 5.2 and 3 μ_B; dilute-magnetic semiconductor (B and N) with 3 and 7 μ_B magnetic moments, respectively. In the case of B or N atoms replacing the native C atom, the down-spin channel yields about 1 eV band gap. Interestingly, replacing the Na atoms in the native Na₂C lattice with the Li can result in the formation of magnetic topological insulator phase with nontrivial band gap in the down-spin channel (25 meV and 0.15 eV) and up-spin channel (0.75 eV), in addition exhibit 8 μ_B magnetic moment in the ground state.

Organisation(s)

PhoenixD: Photonics, Optics, and Engineering - Innovation Across Disciplines

External Organisation(s)

Guilan University
University of Antwerp (UAntwerpen)

Type

Article

Journal

Journal of Magnetism and Magnetic Materials

Volume

491

ISSN

0304-8853

Publication date

01.12.2019

Publication status

Published

Peer reviewed

Yes

ASJC Scopus subject areas

Electronic, Optical and Magnetic Materials, Condensed Matter Physics

Electronic version(s)

https://doi.org/10.1016/j.jmmm.2019.165565 (Access: Closed)