层状卤化物双钙钛矿半金属—可在室温下出现？

半金属铁磁体（HMF）在一个自旋通道中存在电子的金属性，而同时在另一个自旋通道中又存在绝缘性，可产生完全的自旋极化电流，并且被认为是从磁性存储器到自旋极化的许多自旋电子学应用的关键候选者隧道设备。为了开发高性能的自旋电子器件，HMF高度需要三个标准：1）高的室温（RT）应用的居里温度（Tc）；2）宽的半金属间隙（ΔHM）从而有效地防止热激发引起的载流子自旋翻转转变，以及3）大块体磁晶各向异性能（MAE）可克服由热波动引起的自旋随机且不可控的切换。尽管人们已从理论和实验角度报道了一些HMF，但它们大多数还不能同时满足所有这些标准。

该研究确定了一种层状卤化双钙钛矿材料（HMFs），Cs4FePb2Cl12，具有高Tc、宽ΔHM和大MAE的半金属基态。清华大学材料科学与工程学院先进材料（MOE）重点实验室的刘剑波教授和北京计算科学研究中心的黄兵研究员共同领导的团队，使用基于第一性原理计算方法，在大量LHDPs中筛选了具有标准化学组成的Cs4MB2X12材料。有趣的是，在几种具有良好动态和热稳定性的化合物中，他们确定Cs4FePb2Cl12可表现出半金属基态，其计算的Tc高于RT（Tc ~450 K）。同时，Cs4FePb2Cl12的ΔHM~0.55 eV较宽、MAE~380μeV/ Fe较大，使Cs4FePb2Cl12成为自旋电子学中最好的半金属材料之一。值得注意的是，当Cs4FePb2Cl12层的厚度减小到单层时，它仍可以以高Tc~370 K和强MAE~318 μeV / Fe维持半金属性。Cs4FePb2Cl12的磁耦合和MAE均可用施加外部应变加以有效地操纵。Cs4FePb2Cl12单层的发现，丰富了2D磁体家族，也有望应用于从传感到数据存储的广泛领域。 该文近期发表于npj Computational Materials5: 114(2019)，英文标题与摘要如下，点击左下角“阅读原文”可以自由获取论文PDF。

Prediction ofroom-temperature half-metallicity in layered halide double perovskites Jian Xu,Changsong Xu,Jian-Bo Liu,LaurentBellaiche,Hongjun Xiang,Bai-Xin Liu &Bing Huang Half-metallic ferromagnets (HMFs) that possess intriguing physical properties with completely spin-polarized current are key candidates for high-efficiency spintronic devices. However, HMFs that could simultaneously have high Curie temperature (Tc), wide half-metallic gap (ΔHM), and large bulk magnetocrystalline anisotropy energy (MAE) are very rare, which significantly restrict their room-temperature (RT) applications. In this article, through materials screening in layered halide double perovskites (LHDPs), we have theoretically identified that Cs4FePb2Cl12, which has good crystallographic, dynamic and thermal stabilities, possesses an intrinsichalf-metallic ground-state with a highTc~450K. Interestingly, the long-range ferromagnetic ordering in bulk Cs4FePb2Cl12is contributed by the strong super-superexchange interactions between the neighboring Fedorbitals mediated by different anionic Clporbitals. The highTcoflayered Cs4FePb2Cl12can be well maintained even in the monolayer limitation, i.e.,Tc~370K for Cs4FePb2Cl12monolayer, which is critical for nanoscale device applications. Moreover, both bulk and monolayer Cs4FePb2Cl12can exhibit wide ΔHM~0.55eV and large MAE >320μeV/Fe, comparable to that of the best HMFs reported in the literature. Our findings can significantly extend the potentials of LHDPs for high-temperature spintronic applications.