Hebei Messi Biology Co., Ltd. pointed out that at present, high-purity nano magnesium oxide is widely used in battery and electronic fields, among which the magnetic material of magnesium oxide is an indicator that customers are more concerned about. It is found that the polycrystalline magnesium oxide has weak ferromagnetism when the macro crystal is nonmagnetic magnesium oxide. The first principle electronic structure method was used to study the magnetism of MgO surface, nanoparticles and grain boundaries.
The results show that the insulating magnesium oxide surface can be conductive and has ferromagnetism related to it; The common feature of magnetic surfaces is the enrichment of oxygen atoms on the surface, including the layer of pure oxygen atoms on the surface and the oxygen atom chains on the surface; Other high crystal face index surfaces also have oxygen atom enrichment regions; The magnetism of MgO nanoparticles appears in the areas where oxygen atoms are enriched, such as the surface with high crystal face index and the edges and top angles at the boundary of different crystal faces. This magnetism formed by oxygen atom enrichment has a wandering feature.
The calculation results of magnesium oxide and grain boundaries show that the magnetism of grain boundaries in polycrystalline samples is very weak without oxygen atom enrichment, while the magnetism of grain boundaries is relatively strong in the case of oxygen atom enrichment. Therefore, it can be inferred that the magnetism of polycrystalline samples mainly occurs in the areas where oxygen atoms are enriched, such as polycrystalline surface, grain surrounded pores, microcrack interfaces, grain boundaries and other crystal defects. This residual magnetism can be weakened or even eliminated through structural optimization processes such as heat treatment.