Full quantum search for high T _c two-dimensional van der Waals ferromagnetic semiconductors

Atomic thin two-dimensional (2D) ferromagnetic (FM) semiconductors with high Curie temperatures (T_c) are essential for future spintronic applications. However, reliable theoretical searching for 2D FM semiconductors is still hard due to the complexity of strong quantum fluctuations in 2D systems. We have proposed a full quantum search (FulQuanS) method to tackle the difficulty, and finally identified five 2D semiconductors of CrX₃ (X = I, Br, Cl), CuCl₃ and FeCl₂ with FM order at finite temperature from the pool of 3721 potential 2D structures. Via the method of renormalized spin wave theory (SW) and quantum Monte Carlo simulations (QMC), we located the T_c for CrX₃ (X = I, Br, Cl), CuCl₃ and FeCl₂ at 48 K, 31 K, 18 K, 74 K and 931 K respectively, which excellently agree with experiments for CrX₃ and reveal the superior performances of the new predicted structures. Furthermore, our QMC results demonstrated that the systems with low-spin numbers and/or low anisotropies have much higher T_c than the estimations of classical models e.g., Monte Carlo simulations based on classical Heisenberg models. Our findings suggest excellent candidates for future room-temperature spintronics, and shed light on the quantum effects inherent in 2D magnetism.