γ-Fe_2O_3/NiO核-壳纳米花的合成、微结构与磁性  

Synthesis, microstructure, and magnetic properties of γ-Fe_2O_3/NiO core/shell nanoflowers

作　　者：李志文[1] 何学敏[1,2] 颜士明[1,3] 宋雪银 乔文[1] 张星[1] 钟伟[1] 都有为[1] 

机构地区：[1]南京大学物理系固体微结构物理国家重点实验室,南京210093 [2]南京邮电大学理学院信息物理研究中心,南京210023 [3]河南工业大学理学院,郑州450001

出　　处：《物理学报》2016年第14期229-237,共9页Acta Physica Sinica

基　　金：国家自然科学基金(批准号:11174132;11474151;U1232210);国家重点基础研究发展计划(批准号:2011CB922102;2012CB932304);江苏省普通高校博士生科研创新计划(批准号:CXZZ13_0035)资助的课题~~

摘　　要：利用溶剂热/热分解的方法合成出微结构可控的γ-Fe_2O_3/NiO核-壳结构纳米花.分析表明NiO壳层是由单晶结构的纳米片构成,这些纳米片不规则地镶嵌在γ-Fe_2O_3核心的表面.Fe3O4/Ni(OH)_2前驱体的煅烧时间对γ-Fe_2O_3/NiO核-壳体系的晶粒生长、NiO相含量和壳层致密度均有很大的影响.振动样品磁强计和超导量子干涉仪的测试分析表明,尺寸效应、NiO相含量和铁磁-反铁磁界面耦合效应是决定γ-Fe_2O_3/NiO核-壳纳米花磁性能的重要因素.随着NiO相含量的增加,磁化强度减小,矫顽力增大.在5 K下,γ-Fe_2O_3/NiO核-壳纳米花表现出一定的交换偏置效应(H_E=46 Oe),这来自于(亚)铁磁性γ-Fe_2O_3和反铁磁性NiO之间的耦合相互作用.与此同时,这种交换耦合效应也进一步提高了样品的矫顽力(H_C=288 Oe).The main purpose of this work is to explore the influences of microstructures on the magnetic properties, as well as the formation mechanism of γ-Fe2O3/NiO core/shell nanoflowers. The synthesis of nanoflower-like samples includes three processes. Firstly, Fe2O3 nanospheres are synthesized by the solvothermal reaction of Fe Cl3 dissolved in ethylene glycol and Na Ac. Secondly, Fe2O3/Ni（OH）2core/shell precursor is fabricated by solvothermal method through using the early Fe2O3 spheres and Ni（NO3）2·6H2O in an ethanol solution. Finally, the precursor Fe2O3/Ni（OH）2is calcined in air at 300？C for 3–6 h, and therefore resulting in γ-Fe2O3/NiO core/shell nanoflowers. Their microstructures are characterized by using XRD, XPS, SEM, HRTEM and SAED techniques. The results show that the final powder samples are γ-Fe2O3/NiO with typical core/shell structure. In this core/shell system, the γ-Fe2O3 sphere acts as core and the NiO acts as shell, which are comprised of many irregular flake-like nanosheets with monocrystalline structure,and these nanosheets are packed together on the surfaces of γ-Fe2O3 spheres. The calcination time of Fe2O3/Ni（OH）2precursor has significant influences on the grain growth, the NiO content and the compactness of NiO shells in theγ-Fe2O3/NiO core/shell system. VSM and SQUID are used to characterize the magnetic properties of γ-Fe2O3/NiO core/shell nanoflowers. The results indicate that the 3 h-calcined sample displays better ferromagnetic properties（such as higher Ms and smaller HC） because of their high γ-Fe2O3 content. In addition, as the coupling interaction between the FM γ-Fe2O3 and AFM NiO components, we observe that the γ-Fe2O3/NiO samples formed in 3 h and 6 h display certain exchange bias（HE = 20 and 46 Oe, respectively）. Such a coupling effect allows a variety of reversal paths for the spins upon cycling the applied field, and thereby resulting in the enhancement of coercivity（HC（FC） = 252 and 288 Oe, respectively）. Further, the values of HE and

关 键 词：相含量 分层结构 界面耦合 交换偏置 

分 类 号：TB383.1[一般工业技术—材料科学与工程]