Two-dimensional (2D) ferromagnetic semiconductors (FMSs) hold exciting and promising potential for application in spintronic devices at the nanoscale. Currently, most 2D FMSs are based on 3d electrons; 4f electrons can provide nontrivial magnetism but have been much less studied to date. This paper presents a theoretical study, via first-principles calculations, of EuSn2X2 (X = P, As) monolayers based on rare-earth cations with f-electrons. The results show that EuSn2X2 monolayers possess a large magnetization (7 μB/Eu), a controllable magnetic anisotropy energy, and a unique d-electron-mediated f–f exchange mechanism. Both types of EuSn2X2 (X = P, As) monolayers are FMSs with indirect bandgaps of 1.00 and 0.99 eV, respectively, based on the Heyd–Scuseria–Ernzerhof (HSE06) method, which can be transform to direct bandgap semiconductors under biaxial strain. Interestingly, under the latter, spin–orbit coupling interaction gradually replaces the dipole–dipole interaction in the dominant position of magnetic anisotropy, resulting in the magnetic easy axis changing from in-plane to the more desirable out-of-plane. Considering their excellent dynamic, thermal, and mechanical stabilities and small cleavage energy, these EuSn2X2 monolayers can be exfoliated from their synthesized bulk. Our study not only helps to understand the properties of 2D 4f rare-earth magnets but also signposts a route toward improving the performance of EuSn2X2 monolayers in nano-electronic devices.

Two-dimensional (2D) material is the promising for next-generation information technology. The recently discovered intrinsic magnetic crystals have simulated a renaissance in 2D spintronics, which provides an ideal platform for exploring novel physical phenomena. However, current experimental trial-and-error methods in discovering new spintronic material are still very expensive and challenging. In contrast, based on well-developed first-principles calculations, computationally designing the spintronic materials provides a more efficient way for exploring new ferromagnetic (FM) materials and understanding the nature of magnetic properties. Several predictions, such as CrI3 monolayer, CrGeTe3 bilayer, CrSBr monolayer, FeCl2 monolayer, and Fe3GeTe2 monolayer have been confirmed by experiments, showing the great performance of computational approaches. This minireview article attempts to give a brief of discovering intrinsic 2D spintronics from theoretical aspect, and in particular, we emphasize roles played by calculation based on first-principles methods in designing 2D FM materials and devices. The current challenges and proposals on future developments of 2D spintronics are also discussed.