多孔CrO$_2$：稀疏锰钡矿氧化物家族中的铁磁半金属成员
Porous CrO$_2$: a ferromagnetic half-metallic member in sparse hollandite oxide family
AI总结：
本研究通过PBE+U方法预测出一种新型多孔锰钡矿型CrO$_2$多晶型，证实其为铁磁半金属，揭示了其磁性起源及结构-电子-磁性能关联，验证了压力和应变下的性能稳定性，并探究了II型外尔点的演化。
摘要：
本研究采用PBE+U方法预测出一种稳定的CrO$_2$多晶型。该多孔材料与α-MnO$_2$具有同构性，是稀疏锰钡矿材料组中第二种过渡金属氧化物。但与α-MnO$_2$的反铁磁半导体特性不同，该材料被证实为铁磁半金属。在费米能级处，空穴口袋主要由O-2p轨道贡献，而电子口袋则主要由Cr-3d_{xy}和Cr-3d_{x^2-y^2}贡献。轨道混合引发的负电荷转移与费米能级附近的扩展反键态共同作用，是该结构呈现半金属铁磁特性的原因。通过对金红石型与锰钡矿型CrO$_2$以及锰钡矿型MnO$_2$结构的对比研究，阐明了结构、电子与磁性能之间的相互作用。该材料在水热压力下表现出稳定的磁特性，且能带拓扑结构在单轴应变下保持不变。研究还观测到适度的磁晶各向异性，且其与弹性常数的各向异性存在对应关系。此外，本文还探究了II型外尔点的存在及其在压力下的演化规律。
英文摘要：
A stable polymorph of CrO$_2$ is predicted using PBE+U method. The porous material is isostructural with $α-$MnO$_2$ making it the second transition metal oxide in sparse hollandite group of materials. However, unlike the anti-ferromagnetic semiconducting character of the $α-$MnO$_2$, it is found to be a ferromagnetic half-metal. At Fermi level, the hole pocket has ample contribution from O$-2p$ orbital, though, the electron pocket is mostly contributed by Cr$-3d_{xy}$ and Cr$-3d_{x^2-y^2}$. A combination of negative charge transfer through orbital mixing and extended anti-bonding state near Fermi level is responsible for the half-metallic ferromagnetic character of the structure. A comparative study of rutile and hollandite CrO$_2$ and hollandite MnO$_2$ structures delineate the interplay between structural, electronic and magnetic properties. The material shows a robust magnetic character under hydrothermal pressure, as well as, the band topology is conserved under uniaxial strain. Moderate magneto-crystalline anisotropy is observed and it shows a correspondence with the anisotropy of elastic constants. Occurrence of type$-$II Weyl nodes and their evolution under pressure is explored.
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