摆线型 NiBr₂的电子结构及电输运性质的各向异性

Electronic Structure and Anisotropy of Electrical Transport Properties of Cycloidal Type NiBr₂

摘要

采用多尺度计算模拟研究 NiBr₂单层材料晶格应变对磁态稳定性的调控机制,分析其电子结构与电输运各向异性的物理起源.结合密度泛函理论(DFT)+U 与基于 Perdew-Burke-Ernzerhof(PBE)泛函的PBE0杂化泛函精确修正电子结构,利用PBE能量计算确定稳定磁构型,并借助 AMSET 软件模拟300~900K 下的电导率(σ)和Seebeck系数(S),分析载流子浓度与输运行为的关联.结果表明:当晶格常数为0.369nm 时,摆线型螺旋磁序能量最低,与实验观测的非共线磁序吻合;PBE0计算所得带隙值为3.60eV,与实验值(3.4±0.2)eV 相符;σ呈极强各向异性,室温下σ_a/σ_c≈125,900K 下σ_a/σ_c≈480,这是由于c轴极高的真空势垒抑制所致;S 在p型掺杂中存在临界载流子浓度阈值,超过阈值后发生反转(S_c>S_a),这是由于高浓度下a轴态密度变化率饱和及c 轴平缓能带贡献增强所致.该结果揭示了NiBr₂单层电输运性质的各向异性,为低维磁性半导体器件的实验探索提供了理论基础.

Abstract

We used multi-scale computational simulations to study the modulation mechanisms by which lattice strain regulated magnetic stability of monolayer NiBr₂, and analyzed the physical origins of its electronic structure and electrical transport anisotropy. We combined density functional theory (DFT)+U with Perdew-Burke-Ernzerhof (PBE) functional based PBE0 hybrid functional to accurately modify the electronic structure, determined the stable magnetic structure by using energy calcuations of PBE, and simulated the electrical conductivity (σ) and the Seebeck coefficient (S) at 300—900K using AMSET to analyze the correlation between carrier concentration and transport behavior. The results show that when a lattice constant is 0.369nm, the energy of the cycloidal spiral magnetic order is the lowest, which is consistent with the non-collinear magnetic order observed in the experiment. The bandgap value of PBE0-calculated (3.60eV) is same as the experimental value ((3.4±0.2)eV). σ exhibits extreme anisotropy, σ_a/σ_c≈125 at room temperature, σ_a/σ_c≈480 at 900K, this is due to the extremely high vacuum potential barrier suppression along the c-axis. S exhibits a critical carrier concentration threshold in p-type doping, which reverses after exceeding the threshold (S_c>S_a). This is due to the saturation of the density-of-states gradient along the a-axis at high carrier densities and the enhanced contribution from dispersionless bands along the c-axis. These results reveal the anisotropy of electrical transport properties of monolayer NiBr₂, providing a theoretical foundation for the experimental exploration of low-dimensional magnetic semiconductor devices.

关键词

溴化镍 / 密度泛函理论 / 非共线磁结构 / 电输运性质 / 第一性原理 / 各向异性

Key words

nickel bromide / density functional theory / noncollinear magnetic structure / electrical transport property / first principles / anisotropy

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基金资助

山西省优秀博士来晋工作科研启动项目(601499)