单颗粒链CoFe2O4纳米纤维磁结构的电子全息研究及磁化翻转机制

Magnetic structure of single-particle-chain CoFe2O4 nanofibre directly imaged by off-axis electron holography and its magnetic reversal mechanism

研究低维尖晶石型铁氧体材料微结构与磁结构之间的构效关系,对于丰富基础磁学理论以及设计新型的磁学电子器件具有重要的指导意义。本文采用静电纺丝法制备了单颗粒链的CoFe2O4纳米纤维,利用球差校正透射电镜对其形貌、化学成份、离子占位以及两颗粒之间的界面进行了系统地表征,结果表明纳米纤维具有连续的形貌结构和相对均匀的化学组分分布,基本结构由单个颗粒沿着纤维长轴堆垛生长而成,每个颗粒均是单晶,具有随机的晶体取向。随后利用离轴电子全息术对单根CoFe2O4纳米纤维的磁结构进行了观测,得到其零场下的磁化分布图。理论计算和微磁学模拟均表明,制备的单颗粒链CoFe2O4纳米纤维磁化翻转方式为一致翻转。

Investigation on the relationship between the micro-structure and magnetic structure in spinel ferrite materials is significant and essential to not only enrich the fundamental knowledge of magnetic,but also facilitate the designs of desired magnetic electronic devices.In this work,single-particle-chain cobalt CoFe2O4 ferrites were synthesized by electrospinning method,the morphology,chemical composition and interfaces of which were systematically characterized by scanning electron microscope and transmission electron microscopy.The results show that individual nanofibres have a continuous structure and relatively uniform distribution.Lattice-resolution HRTEM images of the interfaces of two neighbored crystallites in a single CoFe2O4 nanofiber demonstrate that individual CoFe2O4 nanoparticles stack along the nanofiber axis and each particle is a single crystal with random crystal orientation.Off-axis electronic holography technique was then employed to directly image the magnetic structure of individual CoFe2O4 nanofibre.Micro-magnetic simulation performed by OOMMF software was carried out to obtain magnetization distribution of a single nanofiber for a comparison with the experimental results,which discovers that the magnetization reversal mechanism for the single-particle-chain CoFe2O4 nanofibre should be governed by the coherent rotation mode.