Electrical tuning of the magnetic properties of 2D magnets: the case of ${\rm Cr}_2{\rm Ge}_2{\rm Te}_6$

TL;DR

This study uses ab initio calculations to explore how electrical doping influences the magnetic properties of monolayer Cr2Ge2Te6, revealing that magnetism can be electrically tuned and is more stable under hole doping.

Contribution

It provides a detailed theoretical analysis of the electrical control of magnetism in 2D Cr2Ge2Te6, highlighting the robustness of magnetic properties under hole doping and the limitations under electron doping.

Findings

Magnetism in Cr2Ge2Te6 is electrically tunable and more robust with hole doping.

The magnetic anisotropy energy vanishes at a specific electron density, indicating a breakdown of localized spin models.

Exchange couplings increase rapidly with electron density, affecting magnetic stability.

Abstract

Motivated by growing interest in atomically-thin van der Waals magnetic materials, we present an {\it ab initio} theoretical study of the dependence of their magnetic properties on the electron/hole density $\rho$ induced via the electrical field effect. By focusing on the case of monolayer ${\rm Cr}_2{\rm Ge}_2{\rm Te}_6$ (a prototypical 2D Ising ferromagnet) and employing a hybrid functional, we first study the dependence of the gap and effective mass on the carrier concentration $\rho$. We then investigate the robustness of magnetism by studying the dependencies of the exchange couplings and magneto-crystalline anisotropy energy (MAE) on $\rho$. In agreement with experimental results, we find that magnetism displays a bipolar electrically-tunable character, which is, however, much more robust for hole ($\rho>0$) rather than electron ($\rho<0$) doping. Indeed, the MAE vanishes for an electron density $\rho\approx - 7.5 \times 10^{13}~{\rm e} \times {\rm cm}^{-2}$, signalling the failure of a localized description based on a Heisenberg-type anisotropic spin Hamiltonian. This is in agreement with the rapid increase of the coupling between fourth-neighbor atoms with increasing electron density.