Doping induced magnetism and half-metallicity in nanoribbons of quartic dispersion materials

TL;DR

This study addresses how quantum confinement from 2D to quasi-1D enhances hole-doped magnetism and half-metallicity in quartic-dispersion materials. Using DFT with edge-structure-aware nanoribbons of GaS, InSe, and TiO$_2$, it shows substantial increases in the spin-polarization energy $E_{sp}$ upon confinement, with maxima up to $E_{sp} \,=\, 103$ meV per carrier in TiO$_2$ nanoribbons. The enhancement is tightly linked to localization of magnetic moments across the ribbon width, quantified by $IPR$, and is strongly influenced by edge passivation and ribbon width, leading to edge- or center-localized magnetization profiles. The results reveal deviations from a simple Stoner mechanism at higher dopings due to deformation of the top valence bands, yet demonstrate robust itinerant magnetism and half-metallicity over wide carrier-density ranges, suggesting broad applicability to other material families with Mexican-hat-type valence bands.

Abstract

Two-dimensional (2D) quartic dispersion materials are known to develop magnetization upon doping. Here we conduct a systematic investigation of magnetization in hole-doped quartic dispersion materials (GaS, InSe, TiO$_{2}$), focusing on the effects of structural confinement from 2D monolayers to quasi-one-dimensional nanoribbons (NRs). Upon hole doping, these NRs develop itinerant magnetization across a broad range of carrier densities and display half-metallic behavior. The spin-polarization energies ($E_{sp}$) of these NRs enhance remarkably relative to their 2D counterparts, with maximum increase being in the case of TiO$_{2}$ from 31 to 103 meV/carrier. The $E_{sp}$ strongly depends on the degree of localization of the magnetic moments along the width of NRs, which is determined by edge passivation and ribbon width. Strong deformation of the topmost valence bands at higher dopings indicates deviation from the Stoner mechanism.

Figures (11)

• Figure 1: Schematic representations of 1T MX and TiO$_{2}$ ZNRs and the unit cells of the corresponding 2D monolayers.
• Figure 2: Spin polarization energies of 2D 1T-phase TiO$_{2}$, InSe, and GaS, along with selected ZNR configurations.
• Figure 3: GaS 1T-P-ZNR8 and 1T-2D a) spin polarization energies and b) magnetic moments per carrier as a function of the carrier density. c) magnetization profiles along the width of NR and d) spin-polarized band structures at selected carrier densities.
• Figure 4: InSe 1T-UP-ZNR6 and 1T-2D a) spin polarization energies and b) magnetic moments per carrier as a function of the carrier density. InSe 1T-UP-ZNR6 c) magnetization profiles along the width of NR and d) spin-polarized band structures at selected carrier densities.
• Figure 5: TiO$_{2}$ 1T-UP-ZNR5 and 1T-2D a) spin polarization energies and b) magnetic moments per carrier as a function of the carrier density. TiO$_{2}$ 1T-UP-ZNR5 c) magnetization profiles along the width of NR and d) spin-polarized band structures at selected carrier densities.