γ射线辐照对MgO单晶的点缺陷组态及磁性的影响

Influence of γ-ray irradiation on the point defect configurations and magnetic properties of MgO single crystals

对(100)取向的MgO单晶进行了不同剂量的60Coγ射线辐照,辐照剂量从30 kGy到1 750 kGy。利用同步辐射漫散射技术以及紫外-可见吸收光谱研究了辐照样品的点缺陷情况,并将实验测量的漫散射结果与理论计算结果进行比对,以获得点缺陷组态的信息。利用超导量子干涉仪(Superconducting Quantum Interference Device,SQUID)测量了样品在不同温度下的磁性质。漫散射和吸收光谱的实验结果表明,经γ射线辐照的MgO单晶产生了阴离子弗伦克尔缺陷,并在室温下没有表现出铁磁性,只是在低温下观察到了顺磁信号,且辐照前后样品在零场冷却和加场冷却下的M-T曲线没有变化,说明阴离子空位没有导致MgO的d0铁磁性。

Background： d0 ferromagnetism challenges the understanding of magnetism in insulators. MgO, which is important for magnetic tunnel junctions, is an ideal material for investigating d0 ferromagnetism. The ferromagnetism in MgO has attracted great interests.Purpose： This study aims toinvestigate the influence ofγ-ray irradiation on point defect configurations and magnetic properties of （100）-oriented MgO single crystals.Methods： The point defect configurations in irradiated-MgO single crystals were experimentally studied using synchrotron radiation diffuse scattering and ultraviolet-visible （UV-vis） absorption spectroscopy. Based on Huang’s scattering theory, the isointensity profile of diffuse scattering was calculated by MATLAB program. The magnetic properties were measured by superconducting quantum interference device （SQUID）.Results：ω-2θscans and rocking curves of （200） and （311） peaks of samples indicated generation of point defects and lattice distortion in irradiated MgO single crystals. The presence of Frenkel defects in irradiated MgO single crystals was evidenced by reciprocal space mappings around the （200） reflection and UV-vis absorption spectra. TheM-H andM-T curves of irradiated MgO single crystals remained the same as that of the unirradiated, demonstrating that the magnetic properties ofirradiated MgO were unchanged.Conclusion： Lots of anion vacancies are generated byγ-rayirradiation in （100） MgO single crystals. However, the anion vacancies cannot induce d0 ferromagnetism in MgO single crystals.