中文摘要：

利用溶剂热/热分解的方法合成出微结构可控的γ-Fe2O3/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-Fe2O3核心的表面.Fe3O4/Ni（OH）2前驱体的煅烧时间对γ-Fe2O3/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-Fe2O3/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-Fe2O3/NiO核-壳纳米花表现出一定的交换偏置效应（HE=46 Oe）,这来自于（亚）铁磁性γ-Fe2O3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（HC=288 Oe）.

英文摘要：

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