CoCr_2O_4纳米晶的制备及其磁性研究

The preparation and magnetic properties of CoCr_2O_4 nanocrystals

通过高分子金属络合物热解法制备了CoCr2O4纳米晶,并对它的表面微结构和磁性能进行了表征。通过高分辨电镜和傅立叶红外光谱的研究发现在平均粒径为12nm的纳米晶表面不仅有晶格缺陷,而且吸附有大量聚合物分解后的有机碎片,这些有机碎片对纳米晶表面磁矩的钉扎以及纳米晶自身的表面晶格缺陷,导致自旋无序的表面和相对自旋有序的核之间产生强的交换耦合作用,从而使得纳米晶呈现出奇特的磁性能,如低温下存在较大的矫顽力和偏置场等。

CoCr_2O_4 nanocrystals with an average grain size about 12nm have been synthesized by thermolysis of polymer-metal complex in vacuum and subsequent oxidation in air. High-resolution transmission electron microscopy (HRTEM) image reveals that surface defects exist at the surface of CoCr_2O_4 nanocrystals. Fourier transform infrared (FT-IR) spectrum indicates that lots of decomposition residues of polymer such as —C—OH groups remain absorbing at the surface of the CoCr_2O_4 nanocrystals. The microstructure features result in a different magnetic spin state between the surface and the inner part, which greatly influence the magnetic properties of the nanocrystals. A large coercivity of 6.33×10~5A/m and an exchange bias field of 3.06×10~4A/m have been observed at 5K in a cooling field of 1T, which may be arising from the exchange coupling between the surface and the inner spins.