The discovery of ferromagnetic two-dimensional van der Waals materials has opened up opportunities to explore intriguing physics and to develop innovative spintronic devices. However, controllable synthesis of these 2D ferromagnets and enhancing their stability under ambient conditions remain challenging. Here, we report chemical vapor deposition growth of air-stable 2D metallic 1T-CrTe₂ ultrathin crystals with controlled thickness. Their long-range ferromagnetic ordering is confirmed by a robust anomalous Hall effect, which has seldom been observed in other layered 2D materials grown by chemical vapor deposition. With reducing the thickness of 1T-CrTe₂ from tens of nanometers to several nanometers, the easy axis changes from in-plane to out-of-plane. Monotonic increase of Curie temperature with the thickness decreasing from ~130.0 to ~7.6 nm is observed. Theoretical calculations indicate that the weakening of the Coulomb screening in the two-dimensional limit plays a crucial role in the change of magnetic properties.

Seeding 2D crystals: Small, single crystals are often used to direct the growth of larger, bulk single crystals. Xu et al. modified these methods to grow single-crystal films of a two-dimensional (2D) semiconductor, 2H molybdenum ditelluride (2H MoTe ₂ ), on an amorphous glass surface. After coating the wafer with a 1T′ MoTe ₂ film, a small 2H MoTe ₂ crystallite was placed on the wafer. The wafer was capped with an alumina film, except for a small hole above the seed region that allowed entry of additional tellurium during the heating process that drove the phase transition and epitaxial growth of 2H MoTe ₂ . Science , this issue p. 195

Calculation and experimental observation of two-dimensional multiferroic CuCrP₂S₆.

Recently reported with nontrivial topological properties and magnetic orders, ${\mathrm{MnBi}}_2{\mathrm{Te}}_4$ is an intrinsic, magnetic topological insulator which holds promise for exploring exotic quantum phenomena such as the quantum anomalous Hall effect. However, the layer-dependent magnetism of ${\mathrm{MnBi}}_2{\mathrm{Te}}_4$, which is fundamental and crucial for further exploration of related quantum phenomena in this system, remains elusive. Here, by using polar reflective magnetic circular dichroism spectroscopy, we show that few-layered ${\mathrm{MnBi}}_2{\mathrm{Te}}_4$ exhibits an evident odd-even layer-number effect, i.e., the oscillations of the coercivity of the hysteresis loop (at ${\mu }_0{H}_c$) and the spin-flop transition (at ${\mu }_0{H}_1$), concerning the Zeeman energy and magnetic anisotropy energy. Noticeably, an anomalous magnetic hysteresis loop is observed in the even-number septuple-layered ${\mathrm{MnBi}}_2{\mathrm{Te}}_4$, which might be attributed to the thickness-independent surface-related magnetization. A linear-chain model is applied to elucidate this odd-even layer-number effect of the spin-flop field and to determine the evolution of the magnetic states when subjected to an external magnetic field. A mean-field method further allows us to fully map the ${\mathrm{MnBi}}_2{\mathrm{Te}}_4$ flake’s magnetic phase diagrams in the parameter space of the magnetic field, layer number, and, especially, temperature. By harnessing the unusual layer-dependent magnetic properties, our work paves the way for further study of quantum phenomena of ${\mathrm{MnBi}}_2{\mathrm{Te}}_4$.