The Structure And Magnetic Studies Of Transition Metal Oxide Magnetic Semiconductor: Co₃O₄ And Co-doped ZnO

Due to high temperature ferromagnetism,3d transition metal oxide magnetic semiconductor (OMS) has a broad prospect in the future spintronic devices. Manipulating ferromagnetic interactions and distribution of magnetic ions in OMS are crucial to the promotion of spintronic devices for practical applications. X-ray absorption fine structure (XAFS), high resolution transmission electron microscopy (HRTEM), superconducting quantum interference device (SQUID), X-ray photoelectron spectroscopy (XPS), were mainly used to study on manipulating the ferromagnetism in Co3O4 quantum dots by graphene and mechanism of mediating distribution of magnetic Co ions in Co-doped ZnO via codopants. These results provide the experimental and theoretical basis for people to find and synthesize available magnetic semiconductors.1、Manipulating the ferromagnetism in Co3O4 quantum dots by grapheneXAFS, XPS, HRTEM and SQUID were mainly adopted to study the microscopic mechanism of manipulating the ferromagnetism in Co3O4 quantum dots by RGO. SQUID measurements shows that after hybridization with RGO, both the remanence magnetization and coercive force of the Co3O4 QDs are increased by 5 times, namely, from 100 to 513 Oe and from 0.4 to 2.2 emu/g, respectively. XAFS and XPS results further show that the electron-transfer from RGO to Co3O4 occurs and leads to the conversion of Co3+ ions located at the octahedral (Oh)positions into Co2+, which is the intrinsic reason of the magnetic interaction between Co2+(Td) from the antiferromagnetic into ferromagnetism. The results of the study provide a new way for people to obtain ferromagnetic interaction in antiferromagnetic oxides.2、Codopants (Cu、Li、Cr) mediating distribution of magnetic Co ions in Co-doped ZnOX-ray absorption fine structure (XAFS) and X-ray photoelectron spectroscopy (XPS) are combined to study the effect of (Cr, Cu, Li) codopants on the distribution of magnetic Co atoms in Co-doped ZnO thin films. For the single-doping of Co in ZnO, there are two occupation sites of Co in ZnO:the substitutional sites for Zn and metallic Co clusters. After Cr doping, the metallic Co clusters vanish and all the Co atoms occupy the substitutional sites. On the contrary, Cu(Li)-codoping further increases the content of metallic Co clusters. In-depth analysis suggests that the distinct roles of Cr and Cu(Li) codopants for mediating the distribution of Co atoms in ZnO are intimately related to the occupation sites of codopants.