Scivetti Ivan, Teobaldi Gilberto
Scientific Computing Department, STFC UKRI, Daresbury Laboratory, Warrington WA4 4FS, United Kingdom.
Stephenson Institute for Renewable Energy, Department of Chemistry, University of Liverpool, Liverpool L69 3BX, United Kingdom.
ACS Appl Mater Interfaces. 2021 Nov 17;13(45):54610-54619. doi: 10.1021/acsami.1c18326. Epub 2021 Nov 3.
Understanding the interplay between strain and nonstoichiometry for the electronic, magnetic, and redox properties of LiMnO films is essential for their development as Li-ion battery (LIB) cathodes, photoelectrodes, and systems for sustainable spintronics applications as well as for emerging applications that combine these technologies. Here, density functional theory (DFT) simulations suggest that compressive strain increases the reduction drive of (111) LiMnO films by inducing >1 eV upshift of the valence band edge. The DFT results indicate that, regardless of the crystallographic orientation for the LiMnO film, biaxial expansion increases the magnetic moments of the Mn atoms. Conversely, biaxial compression reduces them. For ferromagnetic films, these changes can be substantial and as large as over 4 Bohr magnetons per unit cell over the simulated range of strain (from -6 to +3%). The DFT simulations also uncover a compensation mechanism whereby strain induces opposite changes in the magnetic moment of the Mn and O atoms, leading to an overall constant magnetic moment for the ferromagnetic films. The calculated strain-induced changes in atomic magnetic moments reflect modifications in the local electronic hybridization of both the Mn and O atoms, which in turn suggests strain-tunable, local chemical, and electrochemical reactivity. Several energy-favored (110) and (111) ferromagnetic surfaces turn out to be half-metallic with minority-spin band gaps as large as 3.2 eV and compatible with spin-dependent electron-transport and possible spin-dependent electrochemical and electrocatalytic properties. The resilience of the ferromagnetic, half-metallic states to surface nonstoichiometry and compositional changes invites exploration of the potential of LiMnO thin films for sustainable spintronic applications beyond state-of-the-art, rare-earth metal-based, ferromagnetic half-metallic oxides.
理解LiMnO薄膜的应变与非化学计量比之间的相互作用对于其作为锂离子电池（LIB）阴极、光电极以及可持续自旋电子学应用系统的发展至关重要，对于结合这些技术的新兴应用也是如此。在此，密度泛函理论（DFT）模拟表明，压缩应变通过诱导价带边缘向上移动>1 eV来增加(111) LiMnO薄膜的还原驱动力。DFT结果表明，无论LiMnO薄膜的晶体取向如何，双轴膨胀都会增加Mn原子的磁矩。相反，双轴压缩会降低磁矩。对于铁磁薄膜，在模拟的应变范围内（从-6%到+3%），这些变化可能很大，每单位晶胞高达4个以上玻尔磁子。DFT模拟还揭示了一种补偿机制，即应变会在Mn和O原子的磁矩中引起相反的变化，从而导致铁磁薄膜的总磁矩保持恒定。计算得出的应变诱导的原子磁矩变化反映了Mn和O原子局部电子杂化的改变，这反过来表明应变可调的局部化学和电化学反应性。几个能量有利的(110)和(111)铁磁表面结果证明是半金属的，少数自旋带隙高达3.2 eV，与自旋相关的电子传输以及可能的自旋相关的电化学和电催化性质兼容。铁磁半金属态对表面非化学计量比和成分变化的弹性促使人们探索LiMnO薄膜在超越现有基于稀土金属的铁磁半金属氧化物的可持续自旋电子学应用中的潜力。
