【作者】 胡学让；

【导师】 袁俊；

【作者基本信息】 清华大学 ， 材料科学与工程， 2009， 博士

【摘要】 L1₀-FePt具有超高的单轴磁晶各向异性Ku,被认为在将来超高密度垂直磁记录介质中具有良好的应用潜力。本论文结合薄膜生长技术和高空间分辨电子显微术,对L1₀-FePt的结构控制、磁性能与生长条件的关系、小晶粒的有序化等问题进行了研究,并发展相关电子显微方法研究L1₀-FePt的磁二向色性。为了实现垂直记录,在非晶基底上生长了Pt/Fe多层膜,研究制备条件对L1₀-FePt的[001]垂直取向度的影响。发现退火条件对薄膜[001]垂直取向影响很小,而减小Fe层生长速率并提高生长温度能少量提高薄膜[001]垂直取向度。在MgO单晶基底上外延生长了[001]垂直取向的L1₀-FePt薄膜,研究了薄膜磁性能与生长条件的关系。针对L1₀-FePt矫顽力过高的问题,在多层膜快速退火中引入氧化,制备了Fe₃O₄/L1₀-FePt交换耦合双层膜。微磁模拟表明,Fe₃O₄厚度不能超过约10 nm,Fe₃O₄的引入可以使L1₀-FePt的矫顽力降低约28.6%。L1₀-FePt的磁性严重依赖于其化学有序度。利用球差校正高分辨电子显微术对单个十面体FePt颗粒的有序状态进行了研究,发现颗粒图像上最里面5层{002}面原子图像的积分强度随层数发生周期性起伏。多层法图像模拟结果表明这种周期性起伏不会出现在无序的FePt十面体上,实验十面体的最里面的五层{002}面为化学有序,外面三层的有序状态则不能完全确定。这些结果证明FePt颗粒小至3.4 nm时仍然可以是有序的。利用电子能量损矢谱技术对FePt相关材料进行了研究。对Fe₃O₄/L1₀-FePt双层膜的能量损失断面图（ELSP）研究,得到了Fe-L边的化学位移信息,结合氧元素面分布情况,推测氧在氧化过程中进入L1₀-FePt中,并在晶界形成氧化前驱体。结合ELSP和多元统计方法,发展了获得各向异性材料二向色性谱的实验方法。利用单根多壁碳纳米管的C-K边ELSP谱进行验证,获得了本征的平均谱和二向色性谱。利用ELSP-多元统计方法对单个L1₀-FePt颗粒的Fe-L边进行了研究,获得了二向色性信息,这种二向色性是由磁各向异性引起的。这种电子能量损失谱的磁线性二向色性可以用来研究磁性材料的磁矩信息。更多还原

【Abstract】 Because of its ultra-high magnetocrystalline anisotropy Ku, L1₀-FePt has great application potential for future ultra-high density perpendicular magnetic recording media. In this thesis we have combined the thin film technique with high resolution electron microscopy, investigating the structure control of the L1₀-FePt thin film, the relationship between growth conditions and the magnetic properties and the ordering state of small FePt nanoparticle. We have also tried to develop electron energy-loss spectroscopy based method to investigate the magnetic linear dichroism of L1₀-FePt.In pursuance of high density perpendicular recording, we have investigated the influence of the fabricating conditions on the degree of [001] perpendicular orientation of Pt/Fe multilayer grown on amorphous substrate. It was found that the annealing temperature and the annealing time did not have much effect on the degree of [001] perpendicular orientation, while this [001] perpendicular orientation degree can be promoted partly when decrease the growth rate of the Fe layer at elevated temperature. Perfect [001] perpendicular oriented L1₀-FePt thin film was fabricated epitaxially on MgO substrate and the magnetic properties were investigated as a function of the growth conditions. In order to solve the high coercivity problem associated with its high magnetocrystalline anisotropy in L1₀-FePt, Pt/Fe multilayer was rapid thermally annealed while oxidation was introduced to fabricate exchange-coupled Fe₃O₄/L1₀-FePt bilayer. Micromagnetic simulation results indicate that the thickness of the Fe₃O₄ layer should smaller than a critical value which is about 10 nm. The introduction of the Fe₃O₄ layer can reduce the coercivity of L1₀-FePt by about 28.6%.The magnetic properties of L1₀-FePt depend strongly on the degree of chemical ordering. The ordering state of a single FePt decahedron nanoparticle was studied using aberration-corrected high resolution transmission electron microscopy （HRTEM）. The HRTEM image of this particle indicate that the integrated intensity of the {002} layer atoms oscillated periodically from one shell to another for the inner five {002} shells while the outer three {002} shells did not show this kind of oscillation. Multislice image simulation results indicate that this intensity oscillation cannot be found in the images of disordered FePt decahedrons. The experimental decahedron may be ordered for the inner five {002} shells and the ordering state for the outer three shells remains unknown. Our results show that FePt particle, as small as 3.4 nm, can still be ordered. Even though, multiple twinning causes an effective reduction of the magnetic anisotropy.We have employed electron energy-loss spectroscopy to study the FePt related materials. Using energy-loss spectroscopic profiling （ELSP） technique, we obtained the chemical shift information for Fe-L edge. Combined with oxygen elemental mapping results, it was proposed that oxygen diffused into the L1₀-FePt layer to form oxidation precursor along the grain boundary. We have also combined the ELSP method with multivariate statistical analysis （MSA） method to develop a method of experimentally measuring the dichroic signals in an anisotropic material. It was tested on the C-K ELSP images from a single multi-wall carbon nanotube and the intrinsic averaged spectrum and the dichroic spectrum were successfully recovered from MSA processing. We used this ELSP-MSA technique to investigate the magnetic anisotropy of a single L1₀-FePt particle Fe-L edge image. The dichroic like signal was recovered which was due to its magnetic anisotropy. This kind of magnetic linear dichroism can be used to study the magnetic moment of magnetic materials.更多还原