Emergence of 2D high-temperature nodal-line half-metal in monolayer AgN

Two-dimensional half-metals MSi2N4 (M = Al, Ga, In, Tl) with intrinsic p-type ferromagnetism and ultrawide bandgaps

Intrinsic half-metallic nanomaterials with 100% spin polarization are highly demanded for next-generation spintronic devices. Here, by using first-principles calculations, we have designed a class of new two-dimensional (2D) p-type half-metals, MSi2N4 (M = Al, Ga, In and Tl), which show high mechanical, thermal and dynamic stabilities. MSi2N4 not only have ultrawide electronic bandgaps for spin-up channels in the range of 4.05 to 6.82 eV but also have large half-metallic gaps in the range of 0.75 to 1.47 eV, which are large enough to prevent the spin-flip transition. The calculated magnetic moment is 1 μB per cell, resulting from polarized N1-px/py orbitals. Moreover, MSi2N4 possess robust long-range ferromagnetic orderings with Curie temperatures in the range of 35-140 K, originating from the interplay of N1-M-N1 superexchange interactions. Furthermore, spin dependent electronic transport calculations reveal 100% spin polarization. Our results highlight new promising 2D ferromagnetic half-metals toward future spintronic applications.

Magnetic topological materials in two-dimensional: theory, material realization and application prospects

Two-dimensional (2D) magnetism and nontrivial band topology are both areas of research that are currently receiving significant attention in the study of 2D materials. Recently, a novel class of materials has emerged, known as 2D magnetic topological materials, which elegantly combine 2D magnetism and nontrivial topology. This field has garnered increasing interest, especially due to the emergence of several novel magnetic topological states that have been generalized into the 2D scale. These states include antiferromagnetic topological insulators/semimetals, second-order topological insulators, and topological half-metals. Despite the rapid advancements in this emerging research field in recent years, there have been few comprehensive summaries of the state-of-the-art progress. Therefore, this review aims to provide a thorough analysis of current progress on 2D magnetic topological materials. We cover various 2D magnetic topological insulators, a range of 2D magnetic topological semimetals, and the novel 2D topological half-metals, systematically analyzing the basic topological theory, the course of development, the material realization, and potential applications. Finally, we discuss the challenges and prospects for 2D magnetic topological materials, highlighting the potential for future breakthroughs in this exciting field.

Two-dimensional half-metallicity and fully spin-polarized topological fermions in monolayer EuOBr

Two-dimensional (2D) half-metal and topological states have been the current research focus in condensed matter physics. Herein, we report a novel 2D material named EuOBr monolayer, which can simultaneously show 2D half-metal and topological fermions. This material shows a metallic state in the spin-up channel but a large insulating gap of 4.38 eV in the spin-down channel. In the conducting spin channel, the EuOBr monolayer shows the coexistence of Weyl points and nodal-lines near the Fermi level. These nodal-lines are classified by type-I, hybrid, closed, and open nodal-lines. The symmetry analysis suggests these nodal-lines are protected by the mirror symmetry, which cannot be broken even spin-orbit coupling is included because the ground magnetization direction in the material is out-of-plane [001]. The topological fermions in the EuOBr monolayer are fully spin-polarized, which can be meaningful for future applications in topological spintronic nano-devices.

Nodal-loop half metallicity in a two-dimensional Fe4N2 pentagon crystal with room-temperature ferromagnetism

Two-dimensional (2D) materials with fully spin-polarized nodal-loop band crossing are a class of topological magnetic materials, holding promise for high-speed low-dissipation spintronic devices. Recently, several 2D nodal-loop materials have been reported in theory and experiment, such as Cu₂Si, Be₂C, CuSe, and Cr₂S₃ monolayers, adopting triangular, tetragonal, hexagonal, or complex lattices. However, a 2D nodal-loop half metal with room-temperature magnetism is still less reported. Here, we report that the 2D Fe₄N₂ pentagon crystal is a nodal-loop half metal with room-temperature magnetism over 428 K and a global minimum structure via first-principles calculations and global structure search. The Dirac nodal lines in Fe₄N₂ form a flat nodal loop at the Fermi level and a spin-polarized type-II nodal-loop above the Fermi level, which are protected by mirror symmetry. Our results establish Fe₄N₂ as a platform to obtain nodal-loop half metallicity in the 2D pentagon lattice and provide opportunities to build high-speed low-dissipation spintronics in the nanoscale.