Abstract The structural and magnetic behavior of monodispersed uncoated Fe3O4 nanoparticles (average particle size = 6 nm) and silver coating of mean thickness 1.5 nm and 2 nm prepared in an emulsion was investigated. The structural and magnetic analysis indicated the formation of a tri layer structure comprising of a disordered magnetic layer of diffused core present in between magnetic core and non-magnetic shell. The nanocrystals with thicker nanoshells exhibit superparamagnetic properties showing decrease in blocking temperatures with increasing shell thickness, whereas the particles of larger diameter are ferrimagnetic at room temperature. The value of saturation magnetization are smaller than those obtained for bulk magnetite emphasizing the presence of a disordered spin layer due to unsaturated iron ions at the surface in case of uncoated magnetite nanoparticles and at the interface for coated ones. The spin canting at the interface, surface strain and increased magnetoelastic anisotropy are some other factors influencing the magnetic properties of these nanoparticles.

中文翻译：

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银纳米壳对 Fe 3 O 4 纳米粒子结构和磁性行为的影响

摘要 研究了在乳液中制备的单分散未涂覆的 Fe3O4 纳米粒子（平均粒径 = 6 nm）和平均厚度为 1.5 nm 和 2 nm 的银涂层的结构和磁性行为。结构和磁性分析表明形成了三层结构，包括存在于磁芯和非磁性壳之间的扩散芯的无序磁性层。具有较厚纳米壳的纳米晶体表现出超顺磁性，显示出随着壳厚度的增加阻断温度降低，而较大直径的颗粒在室温下是亚铁磁性的。饱和磁化强度的值小于块状磁铁矿获得的值，强调在未涂覆的磁铁矿纳米粒子的情况下在表面和在涂层纳米粒子的界面处由于不饱和铁离子存在无序自旋层。界面处的自旋倾斜、表面应变和增加的磁弹性各向异性是影响这些纳米粒子磁性的其他一些因素。