超顺磁性
微晶
材料科学
各向异性能量
矫顽力
透射电子显微镜
凝聚态物理
单一领域
纳米颗粒
分析化学(期刊)
磁铁矿
核磁共振
磁各向异性
磁化
纳米技术
磁场
化学
物理
冶金
色谱法
量子力学
作者
Sneha Upadhyay,Kinnari Parekh,Brajesh Pandey
标识
DOI:10.1016/j.jallcom.2016.03.279
摘要
Structural and magnetic properties of chemically synthesized magnetite nanoparticles have been studied using X-ray diffraction, Transmission Electron Microscopy and Vibrating Sample Magnetometer. Magnetically the synthesized nanoparticles are ranging from superparamagnetic to multi domain state. Average crystallite size of the synthesized magnetite nanoparticles were determined using X-ray line broadening and are found to be in the range of 9–53 nm. On the other hand, the TEM images show that the size is ranging between 7.9 and 200 nm with the transition from spherical superparamagnetic particles to faceted cubic multi domain particles. Magnetic parameters of the samples show a strong dependence on average crystallite size. The ratio of coercive field at 20 K to that at 300 K (Hc (20 K)/Hc (300 K)) increased sharply with decrease in crystallite size. A critical crystallite diameter of order 36 nm may be inferred as boundary between single domain to multi domain transition. Zero-field-cooled (ZFC) and field-cooled (FC) measurements at 10 Oe field validate the same for smallest and largest size samples, confirming that the anisotropy energy is greater than thermal energy upto 300 K temperature. For 9 nm sample broad ZFC curve with overlapping of FC curve is observed just at 300 K, indicating the effect of strong dipolar field in superparamagnetic system.
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