Shah Lubna R, Ali Bakhtyar, Zhu Hao, Wang W G, Song Y Q, Zhang H W, Shah S I, Xiao J Q
Physics and Astronomy, University of Delaware, Newark, DE 19716, USA.
J Phys Condens Matter. 2009 Dec 2;21(48):486004. doi: 10.1088/0953-8984/21/48/486004. Epub 2009 Nov 11.
Room temperature ferromagnetism in polycrystalline Co(x)Ce(1-x)O(2-δ) (0.001≤x≤0.10) bulk samples has been investigated. Annealing in the forming gas transformed the as-prepared paramagnetic into a ferromagnetic insulating material with over two orders of magnitude enhancement (from 3.7 × 10(-2) to 1.24 μ(B)/Co) in the magnetization. Structural characterization of both the as-prepared and H(2)-treated samples showed a single phase material. The incorporation of Co with the formation of oxygen vacancies in the oxide lattice was revealed by x-ray photoelectron spectroscopy (XPS). The presence of oxygen vacancies is indicated by the existence of mixed valence states of cerium (Ce(4+) and Ce(3+)) in the high resolution XPS 3d spectrum. The role of the donor defects (oxygen vacancies) has been verified through the removal of oxygen vacancies. The ferromagnetic insulating ground state has been explained in terms of the interaction of the F(+) center and 3d magnetic cations. The connection between magnetic properties, electronic structure of the magnetic impurity and donor defect has been established. First principle calculations have been performed using the full potential linearized augmented plane wave method within the density functional theory (DFT) framework; these support our experimental findings. Both the experiment and calculations reinforced the crucial role of oxygen vacancies.
对多晶Co(x)Ce(1 - x)O(2 - δ)（0.001≤x≤0.10）块状样品的室温铁磁性进行了研究。在形成气体中退火将制备好的顺磁性样品转变为铁磁性绝缘材料，其磁化强度增强了两个数量级以上（从3.7×10⁻²增加到1.24 μ(B)/Co）。对制备好的样品和经过H₂处理的样品进行结构表征，结果显示为单相材料。通过X射线光电子能谱（XPS）揭示了Co在氧化物晶格中的掺入以及氧空位的形成。高分辨率XPS 3d谱中铈（Ce(4⁺)和Ce(3⁺)）的混合价态的存在表明了氧空位的存在。通过去除氧空位验证了施主缺陷（氧空位）的作用。铁磁性绝缘基态是根据F(⁺)中心与3d磁性阳离子的相互作用来解释的。建立了磁性性质、磁性杂质的电子结构与施主缺陷之间的联系。在密度泛函理论（DFT）框架内使用全势线性缀加平面波方法进行了第一性原理计算；这些计算结果支持了我们的实验发现。实验和计算都强化了氧空位的关键作用。
