Hanxiang Wu, Zuoquan Tan, Zhaxi Suonan, Shanshan Chen, Rui Xu, Wei Ji, Zhihai Cheng, and Fei Pang*
Abstract:
Although 2D self-intercalated Cr5Te8 has been successfully synthesized via chemical vapor deposition (CVD), its etching behavior remains largely unexplored. Etching, as the inverse process of material growth, is essential for understanding growth mechanisms and fabricating nanosheet patterns. Herein, we explore the anisotropic etching of 2D Cr5Te8 assisted by an excess Te supply. The etching process initiates from both the surface and the edge, creating distinct holes and nanoribbons with triangular or hexagonal shapes. To the best of our knowledge, this is the first report on controllable anisotropic etching patterns in 2D Cr5Te8. Furthermore, magnetic measurements reveal ferromagnetism in the etched nanosheets with a Curie temperature (TC) of 164 K, slightly lower than that of the unetched nanosheets. The etched nanosheets exhibit an enhanced saturated magnetic field of 38.5 kOe, approximately 3.2 times that of the unetched nanosheets. This enhancement in the saturated magnetic field is attributed to the pattern-induced strengthening of the reentrant stray field. This study offers a new direction for preparing patterned 2D materials and opens a novel avenue for modulating 2D magnetism.
Altermagnetism has recently drawn considerable attention in three- and two dimensional materials. Here, we extend this concept to quasi-one-dimensional (Q1D) monolayers assembled from single-atomic magnetic chains. Through systematically examining nine types of structures, two stacking orders, and intra /inter-chain magnetic couplings, we identify four out of thirty promising structural prototypes for hosting altermagnetism, which yields 192 potential monolayer materials. We further confirm eight thermodynamically stable Q1D monolayers via high-throughput calculations. Using symmetry analysis and first-principles calculations, we find that the existence of altermagnetism is determined by the type of inter-chain magnetic coupling and predict three intrinsic altermagnets, CrBr3, VBr3, and MnBr3, due to their ferromagnetic inter-chain couplings and five extrinsic ones, CrF3, CrCl3, CrI3, FeCl3, and CoTe3, ascribed to their neglectable or antiferromagnetic inter-chain couplings. Moreover, the inter-chain magnetic coupling here is highly tunable by manipulating the inter-chain spacing, leading to experimentally feasible transitions between altermagnetic and nodal-line semiconducting states. In addition, applying external electric fields can further modulate the spin splitting. Our findings establish a highly tunable family of Q1D altermagnets, offering fundamental insights into the intricate relationship between geometry, electronic structure, and magnetism. These discoveries hold significant promises for experimental realization and future spintronic applications.
FIG. 1. (a) Summary of the emergence of altermagnetism in 1D magnetic chains with different stoichiometric ratios under AA and AB stacking configurations. FM and AFM represent interchain magnetic ordering. The symbol “×” indicates the absence of altermagnetism, while “ ” signifies its emergence. The symbol “/” represents the absence of the AB stacking configuration. Top (upper panel) and side (lower panel) views of the AA-stacked (b) and AB-stacked (c) γ -phase XY2 (X = transition metal, Y = chalcogen/halogen atom) and AA-stacked (d) and AB-stacked (e) β-phase XY3 monolayers. Orange arrows and blue lines illustrate symmetry operations C2x and Mx that connect the sublattices with opposite spins. Red dots P1 to P3 marked in panel (d) indicate structural inversion centers. Orange and blue spheres represent magnetic atoms with up and down majority spins, respectively. J1, J2, and J3 marked in panel (e) represent spin-exchange parameters for the nearest, second-nearest, and third-nearest neighbors, respectively. (f) Diagram of spin-splitting symmetry in the Brillouin zone.
FIG. 2. (a) The screening process of Q1D altermagnets. (b) Top view of spin density distribution and (c) band structure of the CrCl3 monolayer at the interchain spacing of 6.0 Å. The red dot represents the inversion center. The illustration shows the high-symmetry path in the Brillouin zone. (d), (e) The same scheme of (b), (c) for the CrCl3 monolayer with an expanded interchain spacing of 6.40 Å. The red dashed box highlights nodal-line electronic states.
TABLE I. Lattice constants (a and b) and spin-exchange parameters [J1, J2, J3, labeled in Fig. 1(e), in units of meV per magnetic atom] of the eight dynamically stable AA-stacked intrachain AFM β-XY3 Q1D monolayers.
FIG. 3. (a) The energy difference (EAFM -EFM ) as a function of interchain spacing for Q1D VBr3 monolayer. The vertical dashed line indicates the freestanding interchain distance. (b) Band structure of the monolayer VBr3 under interchain of 6.80 Å [labeled as red pentagram in 3(a)]. (c) The energy difference as a function of interchain spacing for Q1D CoTe3 monolayer. (d) Band structure of the monolayer CoTe3 under interchain of 5.10 Å [labeled as red pentagram in 3(c)].
FIG. 4. (a) Band dispersion plots of the highest valence band in freestanding CrCl3 monolayer with interchain FM coupling under varied external electric field. The orange dots indicate the band crossing point along the -S direction. Spin splitting mappings of the highest valence band in the freestanding CrCl3 monolayer (b) without electric field and (c) under an electric field of 0.2 V/Å.
Zeyu Liu, Xianghua Kong, Zewen Wu, Linwei Zhou, Jingsi Qiao and Wei Ji
Abstract:
Moire superlattices in twisted homo-bilayers have revealed exotic electronic states, including unconventional superconductivity and correlated insulating phases. However, their fabrication process often introduces moire disorders, hindering reproducibility and experimental control. Here, we propose an alternative approach using gradient strain to construct moire superlattices in untwisted bilayer graphene (gs-BLG). Through force-field and first-principles calculations, we show that gs-BLG exhibits kagome-like interlayer spacing distributions and strain-tunable kagome electronic bands. The competition between interlayer coupling and in-plane strain relaxation leads to distinct structural deformations, giving rise to three forms of diatomic kagome lattices: subtle, pronounced, and distorted. kagome electronic bands are identified near the Fermi level in their band structures. Modulating strain gradients enables tailoring bandwidths and signs of hopping parameters of these kagome bands, providing a versatile platform for studying exotic electronic phases. Our findings establish gradient strain as an alternative to twist engineering, opening an avenue for exploring emergent electronic phases in graphene-based systems.
Shuo Mi#, Manyu Wang#, Bingxian Shi#, Songyang Li, Xiaoxiao Pei, Yanyan Geng, Shumin Meng, Rui Xu, Li Huang, Wei Ji, Fei Pang, Peng Cheng*, Jianfeng Guo*, and Zhihai Cheng*
Abstract:
Two-dimensional (2D) magnetic materials have predominantly exhibited easy-axis or easy-plane anisotropy and display a high sensitivity to the underlying crystal structure and lattice symmetry. Recently, an in-plane anisotropic 2D ferromagnet of FePd2Te2 has been discovered with intriguing structure and quasi-one-dimensional spin system. Here, we report a real-space investigation of its twinning structure and magnetic states using atomic/magnetic force microscopy (AFM/MFM) combined with scanning tunneling microscopy (STM). The atomic to mesoscale hierarchical structures with the orthogonal and corrugated compressive /tensile(C/T) regions are directly observed due to the intrinsic twinning-domain characteristic. The structure-related intact ferromagnetic (FM), field-induced polarized-FM states and their transitions are comparatively discussed at the mesoscale with the corresponding macroscopic magnetic measurements. Temperature- and field-dependent evolution of magnetic phase are further investigated at the FM and PM states, and summarized to obtain a unique H-T phase diagram of FePd2Te2. Our work provides key results for understanding the complicated magnetic properties of FePd2Te2, and suggests new directions for manipulating magnetic states through the atomic and mesoscale structure engineering.
Two-dimensional (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 the 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 a lateral size of up to ∼0.19 mm and corresponding thickness down to ∼4.8 nm. The role of GaTe is to enhance the efficient Te atom concentration, which promotes the lateral growth of Cr5Te8 nanosheets. Furthermore, our findings reveal the appearance of Cr5Te8 nanosheets exhibiting serrated edges and a stacked structure like those of wedding cakes. Magnetic property measurement revealed the intense out-of-plane ferromagnetism in Cr5Te8, with a Curie temperature (TC) of 172 K. This work paves the way for the controllable growth of submillimeter ultrathin 2D ferromagnetic crystals and lays the foundation for the future synthesis of millimeter ultrathin ferromagnets.
