Juan Dilson, Pruneda Miguel, Ferrari Valeria
Instituto Sabato, UNSAM - CNEA, Av. Gral Paz 1499, San Martín, 1650, Buenos Aires, Argentina.
Catalan Institute of Nanoscience and Nanotechnology - ICN2, CSIC and BIST, Campus UAB, 08193, Bellaterra, Spain.
Sci Rep. 2021 Mar 23;11(1):6706. doi: 10.1038/s41598-021-85945-5.
Oxygen vacancies are common to most metal oxides and usually play a crucial role in determining the properties of the host material. In this work, we perform ab initio calculations to study the influence of vacancies in doped manganites [Formula: see text], varying both the vacancy concentration and the chemical composition within the ferromagnetic-metallic range ([Formula: see text]). We find that oxygen vacancies give rise to a localized electronic level and analyse the effects that the possible occupation of this defect state can have on the physical properties of the host. In particular, we observe a substantial reduction of the exchange energy that favors spin-flipped configurations (local antiferromagnetism), which correlate with the weakening of the double-exchange interaction, the deterioration of the metallicity, and the degradation of ferromagnetism in reduced samples. In agreement with previous studies, vacancies give rise to a lattice expansion when the defect level is unoccupied. However, our calculations suggest that under low Sr concentrations the defect level can be populated, which conversely results in a local reduction of the lattice parameter. Although the exact energy position of this defect level is sensitive to the details of the electronic interactions, we argue that it is not far from the Fermi energy for optimally doped manganites ([Formula: see text]), and thus its occupation could be tuned by controlling the number of available electrons, either with chemical doping or gating. Our results could have important implications for engineering the electronic properties of thin films in oxide compounds.
氧空位在大多数金属氧化物中普遍存在，并且在决定主体材料的性质方面通常起着关键作用。在这项工作中，我们进行了从头算计算，以研究掺杂锰氧化物[化学式：见原文]中空位的影响，同时改变空位浓度和铁磁金属范围内的化学成分（[化学式：见原文]）。我们发现氧空位会产生一个局域电子能级，并分析该缺陷态的可能占据对主体物理性质的影响。特别是，我们观察到有利于自旋翻转构型（局域反铁磁性）的交换能大幅降低，这与双交换相互作用的减弱、金属性的恶化以及还原样品中铁磁性的退化相关。与先前的研究一致，当缺陷能级未被占据时，空位会导致晶格膨胀。然而，我们的计算表明，在低Sr浓度下，缺陷能级可以被占据，这反而会导致晶格参数局部减小。尽管这个缺陷能级的确切能量位置对电子相互作用的细节很敏感，但我们认为对于最佳掺杂的锰氧化物（[化学式：见原文]），它离费米能不远，因此可以通过化学掺杂或栅极控制可用电子的数量来调节其占据情况。我们的结果可能对调控氧化物化合物薄膜的电子性质具有重要意义。
