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实验发现,宏观晶体是非磁性的氧化镁时,其多晶样品有弱铁磁性.本文用第一性原理电子结构方法研究了氧化镁表面、纳米颗粒和晶界的磁性.计算结果表明:绝缘的氧化镁表面可以是导电的,并且有与之相关的铁磁性;磁性表面的共同特征是在表面上有氧原子富集,包括(111)表面的纯氧原子层,(114)表面的氧原子链;其他高晶面指数表面也会有氧原子富集区域;氧化镁纳米颗粒的磁性出现在高晶面指数表面以及不同晶面交界的棱及其顶角等有氧原子富集的区域,这种由氧原子富集而形成的磁性有巡游特征.氧化镁Σ7[111]和Σ5[001]晶界的计算结果表明:在没有氧原子富集的情况下,多晶样品中晶界的磁性很弱,而在有氧原子富集的情况下,晶界磁性比较强.因此可以推断多晶样品的磁性主要出现在多晶表面、晶粒包围孔隙、微裂纹界面、晶界和其他晶体缺陷等有氧原子富集的区域.这种残余磁性可以通过热处理等结构优化过程而削弱甚至消除.
The experimental results show that when the macrocrystal is a non-magnetic magnesium oxide, the polycrystalline samples have weak ferromagnetism.In this paper, the magnetic properties of the surface, the nanoparticles and the grain boundaries of magnesium oxide have been investigated by the first-principles electronic structure method.The calculated results show that the insulating Magnesium oxide surfaces may be electrically conductive and have ferromagnetism associated therewith; a common feature of magnetic surfaces is the enrichment of oxygen atoms on the surface, including pure oxygen atomic layers on the (111) surface, oxygen atoms on the (114) surface Chain; Other high crystal surface index surface will also have oxygen atom enrichment area; Magnesium oxide nanoparticles appear in the high crystal surface index surface and the edge of the different crystal face and its corners and other corners of the oxygen atom enrichment region, The magnetism formed by enrichment of oxygen atoms has cruising characteristics.The calculated results of Σ7 [111] and Σ5 [001] grain boundaries indicate that in the absence of oxygen enrichment, the grain boundary The magnetism is very weak, but in the case of enrichment of oxygen atoms, the grain boundary is relatively magnetic, so it can be inferred that the magnetic properties of the polycrystalline sample mainly appear on the polycrystalline surface, surrounded by pores, micro-cracks, grain boundaries and other crystals Defects such as oxygen enrichment Region. Such residual magnetism may weaken or eliminate the heat treatment process by structure optimization.