Prediction of bipolar VSi2As4 and VGe2As4 monolayers with high Curie temperature and strong magnetocrystalline anisotropy

Recent studies have demonstrated that two-dimensional intrinsic magnetic materials with high Curie temper-ature (Tc) and large magnetic anisotropy energy (MAE) are highly desirable for future spintronics. After careful investigations through density functional theory, bipolar VSi2As4 and VGe2As4 monolayers, with semiconductor valence and conduction band edges fully spin polarized in different spin directions, are demonstrated to be highly stable and have in-plane ferromagnetism (FM) with large MAE of similar to 5.5 meV. The FM interaction is found to be dominated by the superexchange between d orbitals of V atoms through p orbitals of anions. More interestingly, Tc is estimated to be similar to 900 K through Monte Carlo simulation, which is significantly higher than room temperature. In addition, both MAE and Tc can be substantially regulated and increased under biaxial strain and the transition from FM semiconductors to metals will occur. Our calculations and analyses indicate that VSi2As4 and VGe2As4 monolayers are ideal systems for the fundamental understanding of magnetic physics as well as building blocks for magnetoelastic applications, high-temperature, or/and gate-tunable spintronic nanodevices.