Intrinsic magnetism with high critical temperatures and piezoelectricity in 2D transition metal tetraborides

Developing 2D materials with intrinsic magnetism is an essential issue owing to their wide potential applications in spintronics. Here, a type of transition metal tetraborides, TMB4, (TM = Ti-Co) monolayers were systematically investigated by employing first principles calculations. Our results showed that the predicted structures hold buckled motif, ultrahigh stability and large magnetic anisotropy energy. It is revealed that CrB4, MnB4, and FeB4 monolayers are robust ferromagnetism, differently, TiB4, VB4, and CoB4 monolayers are stable anti-ferromagnetism. Based on the Monte Carlo simulation, the critical temperatures of these magnetic systems are around 177-755 K. Most importantly, CoB4 monolayer is confirmed to be an antiferromagnetic semiconductor with out-of-plane magnetic easy axis and out-of-plane piezoelectricity with large piezoelectric stress coefficients. Our study suggests that the 2D TMB(4)s hold promising applications for spintronic devices and piezoelectric devices.