Structure-property relationships have always been guiding principles for materials discovery. Here we explore the relationships to discover two-dimensional (2D) materials with the goal of identifying 2D magnetic semiconductors for spintronics applications. In particular, we report a density functional theory + $U$ study of single-layer antiferromagnetic (AFM) semiconductor ${\mathrm{CoS}}_2$ with the pentagonal structure forming the so-called Cairo tessellation. We find that this single-layer magnet exhibits an indirect band gap of 1.06 eV with electron and hole effective masses of 0.52 and 1.93 $m_0$, respectively, which may lead to relatively high electron mobility. The hybrid density functional theory calculations correct the band gap to 2.24 eV. We also compute the magnetocrystalline anisotropy energy (MAE), showing that the easy axis of the AFM ordering is along the $b$ axis with a sizable MAE of 153 $\mu \mathrm{eV}$ per Co ion. We further calculate the magnon frequencies at different spin-spiral vectors, based on which we estimate the $\mathrm{N}\acute{\text{e}}\mathrm{el}$ temperatures to be 20.4 and 13.3 K using the mean field and random phase approximations, respectively. We then apply biaxial strains to tune the band gap of single-layer pentagonal ${\mathrm{CoS}}_2$. We find that the energy difference between the ferromagnetic and AFM structures strongly depends on the biaxial strain, but the ground state remains the AFM ordering. Although the low critical temperature prohibits the magnetic applications of single-layer pentagonal ${\mathrm{CoS}}_2$ at room temperature, the excellent electrical properties may find single-layer semiconductor applications in optoelectronic nanodevices.

• Received 13 September 2018
• Revised 2 November 2018

DOI:https://doi.org/10.1103/PhysRevB.98.205425