ABSTRACT
The research of two-dimensional multiferroic materials has attracted extensive attention in recent years. In this work, we systematically investigated the multiferroic properties of semi-fluorinated and semi-chlorinated graphene and silylene X2M (X = C, Si; M = F, Cl) monolayers under strain using first principles calculations based on density functional theory. We find that the X2M monolayer has a frustrated antiferromagnetic order, and a large polarization with a high reversal potential barrier. When increasing the applied biaxial tensile strain, the magnetic order remains unchanged, but the polarization flipping potential barrier of X2M gradually decreases. When the strain increases to 35%, although the energy required to flip the fluorine and chlorine atoms is still very high in the C2F and C2Cl monolayers, it goes down to 312.5 meV and 260 meV in unit cells of the Si2F and Si2Cl monolayers, respectively. At the same time, both semi-modified silylenes exhibit metallic ferroelectricity with a band gap of at least 0.275 eV in the direction perpendicular to the plane. The results of these studies show that Si2F and Si2Cl monolayers may become a new generation of information storage materials with magnetoelectric multifunctional properties.
ABSTRACT
Low-dimensional multiferroics are highly desired for applications and contain exotic physical properties. Here we predict a two-dimensional material, C2O2Fe monolayer, through Fe intercalation in the graphene oxide monolayer. The crystal stable texture, chiral spin order, and ferroelectric polarization of the C2O2Fe monolayer are theoretically studied by considering the electron on-site Coulomb interaction and spin orbit coupling, which also manifests the ferroelectric polarization and reversal barrier at 30% biaxial tensile strain comparable with the other two-dimensional ferroelectric materials, such as GeS and GeSe. Moreover, first-principles calculations show that the polarization flipping is accompanied by spin orientation reversal, when the ferroelectric polarization is upward to the plane, a clockwise chiral antiferromagnetic ground state is obtained, while when the polarization is downward, the monolayer shows the anticlockwise chiral antiferromagnetic structure. In this sense, a strong electrically controlled magnetism exists in the designed C2O2Fe monolayer film.
ABSTRACT
In recent years, the research on the physical properties of two-dimensional (2D) materials has attracted much attention. In this paper, the magnetic and ferroelectric (FE) properties of semi-hydrogenated graphene, silylene and germanene X2H (X = C, Si, and Ge) under strain are systematically investigated. The results have shown that X2H is a magnetic FE semiconductor with ferromagnetic (FM) and FE structures, both perpendicular to the plane, a large energy gap, and a high polarization reversal barrier. It is found that both the polarization reversal barrier and the magnitude of FE polarization gradually decrease, but the FM state remains the same, upon gradually increasing the tensile strain. As the tensile strain is increased to 19%, the barriers of the Si2H and Ge2H monolayer films to flip a single valence bond are decreased to 1.123 eV and 0.768 eV, respectively, and the systems still maintain semiconductor characteristics. When the strain is increased to 20%, the films begin to show metallicity in the plane of films, but still have the polarity perpendicular to the plane because of the anisotropy of the band structure. These research results suggest that the magnetoelectric properties of Si2H and Ge2H monolayer films provide the possibility for achieving a new generation of information storage materials.
