Martín-Olivera Lorena, Shchukin Dmitry G, Teobaldi Gilberto
Stephenson Institute for Renewable Energy, Department of Chemistry, The University of Liverpool, L69 3BX Liverpool, United Kingdom.
Beijing Computational Science Research Centre, Beijing 100193, China.
J Phys Chem C Nanomater Interfaces. 2017 Oct 26;121(42):23777-23787. doi: 10.1021/acs.jpcc.7b08476. Epub 2017 Oct 3.
Magnetic hardening and generation of room-temperature ferromagnetism at the interface between originally nonmagnetic transition metals and π-conjugated organics is understood to be promoted by interplay between interfacial charge transfer and relaxation-induced distortion of the metal lattice. The relative importance of the two contributions for magnetic hardening of the metal remains unquantified. Here, we disentangle their role via density functional theory simulation of several models of interfaces between Cu and polymers of different steric hindrance, π-conjugation, and electron-accepting properties: polyethylene, polyacetylene, polyethylene terephthalate, and polyurethane. In the absence of charge transfer, expansion and compression of the Cu face-centered cubic lattice is computed to lead to magnetic hardening and softening, respectively. Contrary to expectations based on the extent of π-conjugation on the organic and resulting charge transfer, the computed magnetic hardening is largest for Cu interfaced with polyethylene and smallest for the Cu-polyacetylene systems as a result of a differently favorable rehybridization leading to different enhancement of exchange interactions and density of states at the Fermi level. It thus transpires that neither the presence of molecular π-conjugation nor substantial charge transfer may be strictly needed for magnetic hardening of Cu-substrates, widening the range of organics of potential interest for enhancement of emergent magnetism at metal-organic interfaces.
在原本非磁性的过渡金属与π共轭有机物的界面处，磁硬化和室温铁磁性的产生被认为是由界面电荷转移与金属晶格弛豫诱导畸变之间的相互作用所促进的。这两种贡献对金属磁硬化的相对重要性尚未得到量化。在这里，我们通过对铜与具有不同空间位阻、π共轭和电子接受特性的聚合物（聚乙烯、聚乙炔、聚对苯二甲酸乙二酯和聚氨酯）之间的几种界面模型进行密度泛函理论模拟，来厘清它们的作用。在没有电荷转移的情况下，计算得出铜面心立方晶格的膨胀和压缩分别会导致磁硬化和磁软化。与基于有机物上π共轭程度及由此产生的电荷转移的预期相反，由于不同程度的有利再杂化导致费米能级处交换相互作用和态密度的不同增强，计算得出铜与聚乙烯界面的磁硬化最大，而铜 - 聚乙炔体系的磁硬化最小。因此可以看出，对于铜衬底的磁硬化而言，分子π共轭的存在或大量电荷转移可能都不是严格必需的，这拓宽了在金属 - 有机界面增强新兴磁性方面具有潜在兴趣的有机物范围。
