Valence band electronic structure of the van der Waals ferromagnetic insulators: VI[Formula: see text] and CrI[Formula: see text]

Influence of Orbital Character on the Ground State Electronic Properties in the van Der Waals Transition Metal Iodides VI3 and CrI3

Two-dimensional van der Waals magnetic semiconductors display emergent chemical and physical properties and hold promise for novel optical, electronic and magnetic "few-layers" functionalities. Transition-metal iodides such as CrI₃ and VI₃ are relevant for future electronic and spintronic applications; however, detailed experimental information on their ground state electronic properties is lacking often due to their challenging chemical environment. By combining X-ray electron spectroscopies and first-principles calculations, we report a complete determination of CrI₃ and VI₃ electronic ground states. We show that the transition metal-induced orbital filling drives the stabilization of distinct electronic phases: a wide bandgap in CrI₃ and a Mott insulating state in VI₃. Comparison of surface-sensitive (angular-resolved photoemission spectroscopy) and bulk-sensitive (X-ray absorption spectroscopy) measurements in VI₃ reveals a surface-only V²⁺ oxidation state, suggesting that ground state electronic properties are strongly influenced by dimensionality effects. Our results have direct implications in band engineering and layer-dependent properties of two-dimensional systems.

Two-dimensional magnetic atomic crystals

Two-dimensional (2D) magnetic crystals show many fascinating physical properties and have potential device applications in many fields. In this paper, the preparation, physical properties and device applications of 2D magnetic atomic crystals are reviewed. First, three preparation methods are presented, including chemical vapor deposition (CVD) molecular beam epitaxy (MBE) and single-crystal exfoliation. Second, physical properties of 2D magnetic atomic crystals, including ferromagnetism, antiferromagnetism, magnetic regulation and anomalous Hall effect are presented. Third, the application of 2D magnetic atomic crystals in heterojunctions reluctance and other aspects are briefly introduced. Finally, the future development direction and possible challenges of 2D magnetic atomic crystals are briefly addressed.

Tuning Magnetic Anisotropy in Two-Dimensional Metal-Semiconductor Janus van der Waals Heterostructures

In the family of 2D materials, atomically thin magnetic systems are relatively new and highly exploitable. Understanding the spin symmetry in such materials has opened a new path toward controlling the magnetic texture. In this study, we have shown that the plethora of different interface formations in the Janus or pure metal-semiconductor-based van der Waals heterostructures 1T-VXY (X, Y = S, Se, Te)-Cr₂A₃B₃ (A, B = I, Cl, Br) allows us to explore and modify the spin-orbit and ligand-metal interactions to fine-tune magnetic anisotropy and different spin symmetries in these systems. We have utilized the interlayer interactions to modulate spin-orbit coupling (SOC) in heterolayers to regulate the magnetic anisotropy in such systems. We have compared systems with the same compositions and different interfaces, for example, Janus VSTe-Janus Cr₂I₃Br₃ and Janus VTeS-Janus Cr₂I₃Br₃, to show that the first one is an Ising ferromagnet, whereas the second one is an XY ferromagnet because of the SOC effect of the heavy ligand atoms.

Nearly Room-Temperature Ferromagnetism in a Pressure-Induced Correlated Metallic State of the van der Waals Insulator CrGeTe_{3}

A complex interplay of different energy scales involving Coulomb repulsion, spin-orbit coupling, and Hund's coupling energy in 2D van der Waals (vdW) material produces a novel emerging physical state. For instance, ferromagnetism in vdW charge transfer insulator CrGeTe_{3} provides a promising platform to simultaneously manipulate the magnetic and electrical properties for potential device implementation using few nanometers thick materials. Here, we show a continuous tuning of magnetic and electrical properties of a CrGeTe_{3} single crystal using pressure. With application of pressure, CrGeTe_{3} transforms from a ferromagnetic insulator with Curie temperature T_{C}∼66  K at ambient condition to a correlated 2D Fermi metal with T_{C} exceeding ∼250  K. Notably, absence of an accompanying structural distortion across the insulator-metal transition (IMT) suggests that the pressure induced modification of electronic ground states is driven by electronic correlation furnishing a rare example of bandwidth-controlled IMT in a vdW material.