具有核／壳结构的纳米复合高频软磁材料

High Frequency Soft Magnetic Nanoparticles with Core/Shell Structures

具有核/壳结构的复合纳米材料兼有外壳层和内核材料的性能,由于其结构和组成能够在nm尺度上进行设计和剪裁,因而具有许多独特的光、电、磁、催化等物理与化学性质。简要介绍了实验室在过渡金属纳米复合高频软磁材料研究方面的最新进展,内容包括:绝缘壳层(如SiO2、Al2O3、C-SiO2等)复合材料,能显著改善过渡金属纳米颗粒的热温度性,有效防止氧化和团聚,具有饱和磁化强度高、高频软磁性能优异的特点;半导体壳层(如ZnO)复合材料,研究了材料的光致发光性能,观测到在ZnO材料中较少出现的700nm发光峰;螺旋碳纳米管与Fe组成的复合材料,实验结果表明该复合材料具有良好的高频吸波性能,有望成为新一代轻质高频吸波材料。

Magnetic nanoparticles with core/shell structures are an important class of functional materials, possessing unique magnetic properties due to their tailored dimensions and compositions. Mainly our ＇recent advances in the preparation and characterizations of high frequency soft magnetic materials with core/shell structures are reviewed. In these magnetic systems we investigated, the magnetic core （Fe, Co, Ni and their alloys） was coated with a layer of i） insulator （such as SiO2, A1203, C-SiO2, etc）, ii） semiconductor （ZnO2）, and iii） helical carbon nanotubes. In the first part of our investigations, the experimental results indicate that the insulator-coated metal nanocomposites are very stable against oxidization in air. The complex permeability study of these materials shows that insulator shell could improve the soft magnetic property, especially in the high-frequency range. In second part, core/shell Fe/ZnO nanocom- posite with average diameter of 200 nm has been synthesized successfully by means of a combined sol-gel/reduction method. The saturation magnetization of the Fe/ZnO samples is relatively high due to the core α-Fe particles. The photoluminescence spectrum recorded at room temperature display ultraviolet band at 390 nm as well as three broader bands at 522, 635, and 700 nm in the region of green to infrared. Such phenomena differ from those reported in previous publications. In the last part, it＇s illustrated how the yield and magnetic properties of double helical carbon nanotubes （HCNTs） generated by the pyrolysis of acetylene over Fe nanoparticles can be manipulated. The HCNTs may be useful as lightweight materials for microwave absorption.