取向尖晶石基薄膜的层状前驱体法制备及其磁学性能研究

发布时间：2018-05-31 16:17

本文选题：类水滑石 + 铁氧体　；参考：《北京化工大学》2010年博士论文

【摘要】： 尖晶石铁氧体薄膜材料在高密度存储、电磁波吸收、磁共振等领域有着广泛的应用前景。研发简便的薄膜制备方法,控制薄膜材料的组成、结构及形貌,进而提高薄膜的磁学性能,成为该领域研究的热点问题。本论文围绕尖晶石铁氧体薄膜材料的构筑及其磁学性能开展基础研究。针对目前该领域研究中的关键科学问题,采用层状前驱体技术,以层状双羟基复合金属氢氧化物(layered double hydroxides,简称LDHs,又叫类水滑石)薄膜为前驱体材料,经高温焙烧制得系列取向尖晶石基铁氧体薄膜材料。通过LDHs薄膜前驱体的制备参数调变及焙烧过程控制,实现了相关铁氧体薄膜材料的组成、形貌、取向的可控制备。同时,表征了溶剂蒸发组装成膜过程,探讨了LDHs薄膜的成膜驱动力及组装机制。最后,研究测试了取向尖晶石基铁氧体薄膜材料的磁学性能。研究工作可望为尖晶石基铁氧体薄膜材料在结构设计、构筑过程控制、应用性能等方面的深入进行奠定一定的实验基础。本论文的创新点和研究结果如下：首先,针对高密度磁存储领域存在的铁磁性纳米粒子“超顺磁限制”这一关键科学问题,以溶剂蒸发制备得到的(00l)取向CoFe-LDHs薄膜为前驱体,在氦气保护下利用LDHs的结构拓扑效应焙烧制备了(111)取向的系列CoFe2O4/CoO纳米复合薄膜。CoFe2O4和CoO界面间强的铁磁／反铁磁相互作用提高了CoFe2O4磁性纳米粒子的热稳定性。与相同粒径的纯相CoFe2O4粒子相比,CoFe2O4/CoO纳米复合薄膜中CoFe2O4粒子的截止温度(TB)提高了100 K以上。同时发现,该薄膜的磁各向异性导致了平行于膜面方向的交换偏置场(HE)的数值大于垂直于膜面条件下的交换偏置场。然后,以(00l)取向的NiFe-LDHs薄膜为前驱体,首先利用LDHs的结构拓扑效应焙烧制备了(111)取向的NiFe2O4/NiO纳米复合薄膜。然后,采用硝酸溶蚀的方法将此复合薄膜中的NiO去除,得到了多孔的(111)取向NiFe2O4薄膜。其表面粗糙程度可通过焙烧温度及酸溶蚀时间来进行调控。经过表面有机化处理后,多孔NiFe2O4薄膜显示出了良好的超疏水性能。随其表面粗糙程度的增强,薄膜与水的接触角变大。磁性及表面浸润性的可控调节使得该多孔尖晶石基铁氧体薄膜有可能在苛刻的外界环境中获得应用。此外,基于LDHs薄膜可控制备的重要意义,通过研究表征溶剂蒸发组装过程,探讨了LDHs薄膜的成膜驱动力及组装机制。在不同晶化温度条件下制备了LDHs纳米粒子。TEM、AFM等表征结果表明,随晶化温度升高LDHs纳米粒子的表观形貌由类球形转变为六方片状,其长厚比(aspect ratio)的增加表明LDHs纳米粒子各向异性程度加强。成膜实验显示,长厚比的大小直接影响溶剂蒸发后最终成膜的连续性及粒子(00l)晶面的取向程度。大的长厚比有利于LDHs纳米粒子间面-面相互作用的增强。在所研究的NiFe-LDHs体系中,发现长厚比大于3时能够制得连续完整的LDHs薄膜。本论文最后还尝试采用了涂覆技术制备LDHs薄膜前驱体,然后经过焙烧处理分别得到了MgFe2O4/MgO和NiFe2O4/NiO复合铁氧体薄膜以及纯相MgFe2O4薄膜。研究表明,上述复合铁氧体薄膜中组分均匀分布,磁性可调；而纯相MgFe2O4薄膜在室温条件下则显示出了优异的“超顺磁”性能。
[Abstract]:In this paper , the composition , morphology and orientation of the thin film are studied by the method of high density storage , electromagnetic wave absorption , magnetic resonance and so on .

The innovation points and research results of this paper are as follows :

The magnetic anisotropy of CoFe2O4 / CoFe2O4 particles increased by more than 100 K . At the same time , it was found that the magnetic anisotropy of the films resulted in the exchange bias field ( HE ) parallel to the direction of the film surface being greater than the exchange bias field perpendicular to the film surface condition .

Then , the NiFe2O4 / NiO nano composite film oriented with ( 111 ) orientation was prepared by using the structure topological effect of LDHs as the precursor . The porous ( 111 ) oriented NiFe2O4 thin film was obtained by using the method of nitric acid dissolution . The surface roughness can be controlled by calcination temperature and acid etching time . After surface organic treatment , the contact angle between the film and water becomes larger . The controllable adjustment of the magnetic and surface wettability makes the porous spinel - based ferrite thin film be used in harsh external environment .

In addition , the film forming driving force and assembly mechanism of LDHs films were investigated based on LDHs film control . LDHs nanoparticles were prepared under different crystallization temperature conditions . The results showed that the apparent morphology of LDHs nanoparticles was enhanced with the crystallization temperature . TEM , AFM and other characterization showed that the morphology of LDHs nanoparticles increased with the crystallization temperature . The results showed that the size of the long - thickness ratio directly affects the continuity of the final film formation and the orientation of the particles ( 00l ) .

In the end , the LDHs film precursor was prepared by coating technique , then MgFe2O4 / MgO and NiFe2O4 / NiO composite ferrite thin films and pure phase MgFe2O4 thin films were obtained after calcination .
while the pure - phase MgFe2O4 film exhibits excellent " super - paramagnetic " performance at room temperature .
【学位授予单位】：北京化工大学
【学位级别】：博士
【学位授予年份】：2010
【分类号】：TB383.1

【参考文献】