Ab initio simulations of defect-based magnetism: the case of CoSi nanowires
Ab initio simulations of defect-based magnetism: the case of CoSi nanowires
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基于缺陷的磁性的从头算模拟：CoSi 纳米线的案例
DOI：
10.1039/c5ra21631a
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发表时间：
2016
期刊：
影响因子：
3.9
通讯作者：
C. Ouyang
中科院分区：
文献类型：
--
作者：
Tai;S. Chiou;J. Lierop;C. Ouyang
用第一性原理计算研究了CoSi-SiO2纳米线中异常铁磁性的来源。虽然以前对铁磁纳米线的实验假设它们的磁性是界面处的金属离子遭受减少的配位的结果，但这种配置的第一原理计算显示，这仅占测量的磁化强度的20%。选区电子衍射（SAED）的透射电子显微镜（TEM）衍射图案收集在金属界面区域表明，超晶格结构是存在的，在相反的散装。我们以CoSi-SiO2纳米线为例，利用模拟的衍射图样，验证了CoSi有序空位超结构对实验的解释。与第一原理模拟，一旦有序的空位与界面Co原子，所得到的模拟结果与实验磁化强度的97%的协议。我们的研究结果清楚地表明，这些内部，有序的空位在纳米线是所观察到的铁磁性的主导机制。态密度计算表明，随着有序空位结构内金属原子配位的增加，整体磁化强度降低。对于CoSi纳米线，不同位置的Co原子磁矩的变化取决于空位的构型，这可以通过键长对Co原子磁矩的影响来理解。根据Bethe-Slater曲线，存在一个必要的键长范围，以使足够的交换能允许铁磁性。我们发现，这个键长起着至关重要的作用，在设置有关空缺的Co时刻的分布。
The source of the unusual ferromagnetism in nanowires (NWs) such as CoSi–SiO2 has been studied by first-principles calculations. While previous experiments on ferromagnetic NWs presumed that their magnetism was the result of metal ions at the interface suffering reduced coordination, first-principles calculations of such a configuration revealed that this would only account for ∼20% of the measured magnetization. Selected area electron diffraction (SAED) transmission electron microscopy (TEM) diffraction patterns collected in the metal interface region indicated that a superlattice structure was present, in contrast to the bulk. We take the case of CoSi–SiO2 NWs, and using simulated diffraction patterns, verify the CoSi ordered vacancy superstructure interpretation of the experiment. With first principles simulations, once the ordered vacancies are incorporated with interface Co atoms, the resulting simulations result in a ∼97% agreement with the experimental magnetization. Our results clearly indicate that these internal, ordered vacancies in NWs are the dominant mechanism for the observed ferromagnetism. Density of states calculations show that as the metal atom's coordination inside the ordered vacancy structures increase, the overall magnetization decreases. For CoSi nanowires, the variations of the Co moments at different sites depend on the vacancy configuration, which can be understood through the effects of the bond lengths on the Co atom moments. According to the Bethe–Slater curve, there is a requisite bond length range for the presence of enough exchange energy to permit ferromagnetism. We find that this bond length plays a crucial role in setting the distribution of Co moments about the vacancies.