Design And Performance Tuning Of Novel Two-dimensional Magnetic Topology Materials

Two-dimensional magnetic topological materials have the following advantages:they have high flexibility and mechanical strength because of their only single-layer atomic structure;due to the interaction of magnetic and topological properties,they can realize very novel physical phenomena,such as quantum Hall effect,quantum anomalous Hall effect,nodal ring,etc.Therefore,two-dimensional magnetic topological materials have become a hot research topic in current physics.In this paper,we propose three two-dimensional magnetic topological materials based on first-principles calculations and discuss their properties and modulation means in detail.First of all,the search for two-dimensional nodal semimetallic materials is a current research hotspot in spintronics,and the design of a two-dimensional nodal ring（NR）material with high Curie temperature and strong robustness to spin-orbit coupling is an even greater challenge.Here,based on first-principles calculations and structural symmetry analysis,we predict that two-dimensional Mn₂N₃ is a nodal line semimetal with three energy bands near the Fermi energy level,consisting of electrons in the same spin channel.An electron-like energy band and two hole-like energy bands cross near the Fermi plane,forming two NRs centered at theΓpoint.symmetry analysis shows that the spin-polarized NRs are robust to spin-orbit coupling effects due to the preservation of horizontal mirror symmetry.Monte Carlo simulations further demonstrate that the Curie temperature of two-dimensional Mn₂N₃reaches 530 K,which is much higher than the room temperature.Notably,2D Mn₂N₃ remains a nodal ring half-metal on h-BN substrates.Our results not only reveal a general framework for designing two-dimensional NR materials,but also provide a possible design material for two-dimensional nodal ring semimetals.Then,we theoretically propose structurally stable monolayer halide chalcogenide Rb₃Pd₂Cl₉.stability calculations and magnetic studies show that monolayer Rb₃Pd₂Cl₉ is structurally stable,the magnetic ground state magnetic moment direction is along the in-plane,and the Berezinskii-Kosterlitz-Thouless phase transition temperature is 301 K.Without considering the spin-orbit,the monolayer Rb₃Pd₂Cl₉ behaves as a conductor when spin-orbit coupling effects are not considered.When spin-orbit coupling and changing the magnetic moment direction are further considered,the monolayer Rb₃Pd₂Cl₉ can open a topologically non-trivial band gap of 1me V-4me V to achieve a high-temperature quantum anomalous Hall effect with C=±1.A small external magnetic field can modulate the sign of the Chen number by changing the magnetization direction.Our findings provide a potentially realizable platform for exploring the quantum anomalous Hall effect and spintronics at high temperatures.Finally,Mxenes can form a class of materials with millions of members by varying the number and type of transition metals and functional groups in the structure,and we have designed two-dimensional ScMoNFBr materials.By means of phonon spectroscopy calculations,molecular dynamics,cohesion energy calculations,and elastic constants,we demonstrate that two-dimensional ScMoNFBr is stable and has the conditions for experimental synthesis.Various anomalous energy calculations and magnetic studies of magnetocrystals indicate that the two-dimensional ScMoNFBr ground state is an out-of-plane ferromagnetic state.The two-dimensional ScMoNFBr is completely occupied by electrons with downward spin direction near the Fermi surface,and the electronic features are completely spin-polarized,which is a necessary condition for the quantum anomalous Hall effect by considering the flipping of the electronic energy bands of d_x² and d_yz orbitals after the spin-orbit coupling.The edge state and Chen calculations prove that the two-dimensional ScMoNFBr is a quantum anomalous Hall effect insulator with Chen number 1.It is hoped that our computational results will provide a possible platform for the study of the quantum anomalous Hall effect.