Two-dimensional (2D) ferromagnets with out-of-plane (OOP) magnetic anisotropy are potential candidates for realizing the next-generation memory devices with ultra-low power consumption and high storage density. However, a scalable approach to synthesize 2D magnets with OOP anisotropy directly on the complimentary metal-oxide semiconductor (CMOS) compatible substrates has not yet been mainly explored, which hinders the practical application of 2D magnets. This work demonstrates a cascaded space confined chemical vapor deposition (CS-CVD) technique to synthesize 2D Fe_xGeTe₂ ferromagnets. The weight fraction of iron (Fe) in the precursor controls the phase purity of the as-grown Fe_xGeTe₂. As a result, high-quality Fe₃GeTe₂ and Fe₅GeTe₂ flakes have been grown selectively using the CS-CVD technique. Curie temperature (T_C) of the as-grown Fe_xGeTe₂ can be up to ~ 280 K, nearly room temperature. The thickness and temperature-dependent magnetic studies on the Fe₅GeTe₂ reveal a 2D Ising to 3D XY behavior. Also, Terahertz spectroscopy experiments on Fe₅GeTe₂ display the highest conductivity among other Fe_xGeTe₂ 2D magnets. The results of this work indicate a scalable pathway for the direct growth and integration of 2D ternary magnets on CMOS-based substrates to develop spintronic memory devices.

The development of information processing devices with minimum carbon emission is crucial in this information age. One of the approaches to tackle this challenge is by using valleys (local extremum points in the momentum space) to encode the information instead of charges. The valley information in some material such as monolayer transition metal dichalcogenide (TMD) can be controlled by using circularly polarized light. This opens a new field called opto-valleytronics. In this article, we first review the valley physics in monolayer TMD and two-dimensional (2D) heterostructure composed of monolayer TMD and other materials. Such 2D heterostructure has been shown to exhibit interesting phenomena such as interlayer exciton, magnetic proximity effect, and spin-orbit proximity effect, which is beneficial for opto-valleytronics application. We then review some of the optical valley control methods that have been used in the monolayer TMD and the 2D heterostructure. Finally, a summary and outlook of the 2D heterostructure opto-valleytronics are given.