Hanxiang Wu, Jianfeng Guo, Hua Xu, Zhaxi Suonan, Shuo Mi, Le Wang, Shanshan Chen, Rui Xu, Wei Ji, Zhihai Cheng, and Fei Pang*
Abstract:
2D non-van der Waals (vdW) Cr5Te8 has attracted widespread research interest for its air stability and thickness-dependent magnetic properties. However, the growth of large-scale ultrathin 2D Cr5Te8 remains challenging. Here, we selected GaTe powder as precursor to supply Te monomers and fabricated submillimeter 2D Cr5Te8 nanosheets. By optimizing the growth temperature and source–substrate distance (DSS), we successfully achieved Cr5Te8 nanosheets with lateral sizes of up to ~0.19 mm and corresponding thicknesses down to ~4.8 nm. The role of GaTe enhances the efficient Te atoms concentration, which promoted the lateral growth of Cr5Te8 nanosheets. Furthermore, our findings reveal the presence of Cr5Te8 nanosheets exhibiting serrated edges and a stacked structure like wedding cakes. Magnetic property measurement revealed the intense out-of-plane ferromagnetism in Cr5Te8, with the Curie temperature (TC) of 172 K. This work paves a way for the controllable growth of the submillimeter ultrathin 2D ferromagnetic crystalline and lays the foundation for the future synthesis of millimeter ultrathin ferromagnets.
Two-dimensional Janus materials exhibit unique physical properties due to broken inversional symmetries. However, it remains elusive to synthesize Janus monolayer crystals with tailored long-range magnetic orders. Here, we show a 2 ×√𝟑 charge density wave (CDW) transition and regulations of magnetization in a uniform Janus CrTeSe monolayer, selectively selenized from a pristine CrTe2 monolayer using molecular beam epitaxy. Scanning transmission electron microscopy images indicate the high quality and uniformity of the Janus structure. Spin-polarized scanning tunneling microscopy/spectroscopy measurements and density functional theory calculations unveil a robust zigzag antiferromagnetic order and the CDW transition in the CrTeSe monolayer. The one-side selenization breaks the vertical inversion symmetry, rotating the magnetic moment directions to the in-plane direction. The CDW transition opens a gap at the Fermi level and reorients the magnetic moments in tilted directions. Our work demonstrates the construction of large-area Janus structures and the tailoring of electronic and magnetic properties of two-dimensional Janus layers.
Renhong Wang (王人宏), Cong Wang (王聪)*, Ruixuan Li (李睿宣), Deping Guo (郭的坪), Jiaqi Dai (戴佳琦), Canbo Zong (宗灿波), Weihan Zhang (张伟 涵), and Wei Ji (季威)*
Abstract:
Kagome materials are known for hosting exotic quantum states, including quantum spin liquids, charge density waves, and unconventional superconductivity. The search for kagome monolayers is driven by their ability to exhibit neat and well-defined kagome bands near the Fermi level, which are more easily realized in the absence of interlayer interactions. However, this absence also destabilizes the monolayer forms of many bulk kagome materials, posing significant challenges to their discovery. In this work, we propose a strategy to address this challenge by utilizing oxygen vacancies in transition metal oxides within a “1+3” design framework. Through high-throughput computational screening of 349 candidate materials, we identified 12 thermodynamically stable kagome monolayers with diverse electronic and magnetic properties. These materials were classified into three categories based on their lattice geometry, symmetry, band gaps, and magnetic configurations. Detailed analysis of three representative monolayers revealed kagome band features near their Fermi levels, with orbital contributions varying between oxygen 2p and transition metal d states. This study demonstrates the feasibility of the “1+3” strategy, offering a promising approach to uncovering low-dimensional kagome materials and advancing the exploration of their quantum phenomena.
The quantum anomalous Hall (QAH) effect in two-dimensional (2D) topological materials has attracted widespread attention due to its potential for dissipationless chiral edge transport without an external magnetic field, which is highly promising for low-power electronic applications. However, identifying materials that exhibit these properties remains particularly challenging, as only a limited number of such materials are known, raising the intriguing question of whether it is possible to induce the QAH effect in materials with ordinary properties through structural modifications. In this work, we grow an unreported 2D titanium selenide (Ti3Se4) on a Cu(111) substrate using molecular beam epitaxy. Low-energy electron diffraction and scanning tunneling microscopy characterizations reveal a brick-like structure. First-principles calculations and X-ray photoelectron spectroscopy measurements confirm its composition to be Ti3Se4. Our calculations further demonstrate that monolayer Ti3Se4, in its grown form on Cu(111), has the potential to host the QAH effect. Interestingly, when we examine its freestanding form, the monolayer transitions from a QAH insulator candidate into a conventional semiconductor, despite only minor differences in their atomic structures. This transition enlightens us that subtle lattice adjustments can induce a transition from semiconductor to QAH properties in freestanding Ti3Se4. This discovery provides a potential route to engineering practical materials that may exhibit the QAH effect.
Qingyang Wang, Mengmeng Niu, Weikang Zhou, Yicheng Ma, Chun Huang, Gege Yang, Yan Shao, Xu Wu, Cong Wang, Wei Ji*, Yeliang Wang*, Jingsi Qiao*
Abstract:
Two-dimensional (2D) multiferroic materials have significant application potential for novel storage devices due to their tunable magnetic and ferroelectric properties. Transition metal phosphorus chalcogenides MPX3 (X = S, Se, and Te) were found to be magnetic and multiferroic with excellent tunability, promising for multifunctionalized applications. In this study, we investigated the antiferromagnetic and antiferroelectric properties of two-dimensional FePX3 and CuFeP2X6 by density functional theory. Monolayer FePS3/FePSe3 and FePTe3 take intralayer zigzag and Neel antiferromagnetic ground states, respectively. This tunability of intralayer magnetism results from the competition between the spin-exchange interactions of the first and second nearest Fe atoms. Bilayer FePX3 shows weak interlayer interactions and keeps electronic and magnetic characteristics similar to those of the monolayer. Moreover, by introducing the nonmagnetic Cu atom into FePX3, the inversion symmetry broken induces CuFeP2X6 to be multiferroic materials. The transition barrier between ferroelectric (FE) and antiferroelectric (AFE) phases in CuFeP2S6 and CuFeP2Se6 is 0.09 and 0.04 eV/f.u., similar to well-known multiferroic CuCrP2S6. FE-to-AFE phase transition is expected to be achieved by applying an electric field and uniaxial strain. CuFeP2Te6 shows the ground state with a distorted paraelectric phase. Our results show the fundamental properties and in-depth understanding of 2D FePX3 and CuFeP2X6, guiding further investigation of 2D multifunctionalized magnetoelectric devices.
