High-Temperature Ferromagnetism in a Two-Dimensional Semiconductor with a Rectangular Spin Lattice

Atomically thin two-dimensional (2D) ferromagnetic (FM) semiconductors with a high Curie temperature (T-C) are essential and highly desired for nanoscale spintronic devices. However, the recently discovered 2D FM semiconductors show rather low T-C (<= 45 K), which limits their practical application. An important reason for the low T-C is the lack of effective spin interactions. Here, we reveal that increasing the number of effective spin interactions by constructing a rectangular spin-lattice can significantly improve the T-C of FM semiconductors. Based on this mechanism, we design a rectangular lattice of the CrO2 monolayer (denoted as R-CrO2) by performing global structural optimizations. The first-principles calculations show that the R-CrO2 is energetically more stable than the previously reported H- and T-CrO2. As expected, the R-CrO2 monolayer is an intrinsic FM semiconductor with T-C up to similar to 370 K, which is more than twice that of the T-CrO2 monolayer (similar to 150 K). This is because the R-CrO2 monolayer possesses four effective spin interactions between adjacent Cr sites, more than that of the T-CrO2 monolayer (3). These findings give rise to a new and efficient design principle for realizing high-temperature 2D FM semiconductors.