Two-dimensional ferromagnetic semiconductors of rare-earth Janus 2H-GdIBr monolayer with large valley polarization

TL;DR

This study predicts that Janus 2H-GdIBr monolayer, a rare-earth ferromagnetic semiconductor, exhibits large valley polarization, high Curie temperature, and tunable magnetic and valley properties under strain and doping, promising for valleytronic applications.

Contribution

First-principles calculations reveal the intrinsic ferromagnetic semiconducting nature and large valley polarization of Janus 2H-GdIBr monolayer, with tunable magnetic and valley features via strain and doping.

Findings

High Curie temperature of 260 K.

Large valley polarization of 118 meV.

Magnetic and valley properties tunable by strain and doping.

Abstract

Based on a rare-earth Gd atom with 4$f$ electrons, through first-principles calculations, we demonstrate that the Janus 2H-GdIBr monolayer exhibits an intrinsic ferromagnetic (FM) semiconductor character with an indirect band gap of 0.75 eV, high Curie temperature T$_{c}$ of 260 K, significant magnetic moment of 8 $\mu_{B}$/f.u. (f.u.=formula unit), in-plane magnetic anisotropy (IMA) and large spontaneous valley polarization of 118 meV. The MAE, inter-atomic distance or angle, and T$_{c}$ can be efficiently modulated by in-plane strains and charge carrier doping. Under the strain range from $-$5% to 5% and charge carrier doping from $-$0.3e to 0.3e/f.u., the system still remains FM ordering and the corresponding T$_{c}$ can be modulated by strains from 233 K to 281 K and by charge carrier doping from 140 K to 245 K. Interestingly, under various strains, the matrix elements differences ($d_{z^{2}}$, $d_{yz}$), ($d_{x^{2}-y^{2}}$, $d_{xy}$) and ($p_{x}$, $p_{y}$) of Gd atoms dominate the MAE behaviors, which originates from the competition between the contributions of Gd-$d$, Gd-$p$ orbitals, and $p$ orbitals of halogen atoms based on the second-order perturbation theory. Inequivalent Dirac valleys are not energetic degenerate due to the time-reversal symmetry breaking in the Janus 2H-GdIBr monolayer. A considerable valley gap between the Berry curvature at the K and K$^{\prime}$ points provides an opportunity to selectively control the valley freedom and to manipulate the anomalous Hall effect. External tensile (compressive) strain further increases (decreases) the valley gap up to a maximum (minimum) value of 158 (37) meV, indicating that the valley polarization in the Janus 2H-GdIBr monolayer is robust to the external strains.