Seto Takafumi, Akinaga Hiroyuki, Takano Fumiyoshi, Koga Kenji, Orii Takaaki, Hirasawa Makoto
J Phys Chem B. 2005 Jul 21;109(28):13403-5. doi: 10.1021/jp052084+.
We have recently developed a method to fabricate monodispersed Ni/NiO core-shell nanoparticles by pulsed laser ablation. In this report, the size-dependent magnetic properties of monodispersed Ni/NiO core-shell nanoparticles were investigated. These nanoparticles were formed in two steps. The first was to fabricate a series of monodispersed Ni nanoparticles of 5 to 20 nm in diameter using a combination of laser ablation and size classification by a low-pressure differential mobility analyzer (DMA). The second step was to oxidize the surfaces of the Ni particles in situ to form core-shell structures. A superconducting quantum interference device (SQUID) magnetometer was used to measure the magnetic properties of nanostructured films prepared by depositing the nanoparticles at room temperature. Ferromagnetism was observed in the magnetic hysteresis loop of the nanostructured films composed of core-shell nanoparticles with core diameters smaller than the superparamagnetic limit, which suggests the spin of Ni core was weakly exchange coupled with antiferromagnetic NiO shell. In contrast, smaller nanoparticles with core diameters of 3.0 nm exhibited superparamagnetism. The drastic change in the hysteresis loops between field-deposited and zero-field-deposited samples was attributable to the strong anisotropy that developed during the magnetic-field-assisted nanostructuring process.
我们最近开发了一种通过脉冲激光烧蚀制备单分散Ni/NiO核壳纳米颗粒的方法。在本报告中，研究了单分散Ni/NiO核壳纳米颗粒的尺寸依赖性磁性能。这些纳米颗粒分两步形成。第一步是结合激光烧蚀和低压差分迁移率分析仪（DMA）进行尺寸分类，制备一系列直径为5至20nm的单分散Ni纳米颗粒。第二步是原位氧化Ni颗粒表面以形成核壳结构。使用超导量子干涉装置（SQUID）磁力计测量通过在室温下沉积纳米颗粒制备的纳米结构薄膜的磁性能。在由核直径小于超顺磁极限的核壳纳米颗粒组成的纳米结构薄膜的磁滞回线中观察到铁磁性，这表明Ni核的自旋与反铁磁性NiO壳层存在弱交换耦合。相比之下，核直径为3.0nm的较小纳米颗粒表现出超顺磁性。场沉积和零场沉积样品之间磁滞回线的剧烈变化归因于磁场辅助纳米结构化过程中产生的强各向异性。
