磁性多层膜系统中的交换偏置、铁磁共振和自旋波性质的研究

【作者】 潘靖；

【导师】 胡经国；

【作者基本信息】 扬州大学 ， 凝聚态物理， 2006， 硕士

【摘要】 近年来,具有新颖物理特性的人工纳米结构的材料引起了人们的极大兴趣,特别是由磁性层和非磁性层材料相间组成的磁性多层膜由于其表现出许多与众不同的磁学及其它物理性质,如层间交换耦合,表(界)面各向异性,巨磁电阻等效应而倍受人们的青睐。它们不仅衍生出了一些全新的物理机制,而且还具有新的重要的高科技应用前景。自从1956年Meiklejohn和Bean在Co(铁磁)/CoO(反铁磁)混合系统中发现交换偏置以来,特别是1991年Dieny在设计的以铁磁/反铁磁双层膜为基础的自旋阀中发现有增强的磁电阻以后,铁磁/反铁磁双层膜在磁传感器、磁记录读出头和随机存储器以及无接触磁控元件等方面得到了广泛地应用。为了提高它的性能,研究铁磁/反铁磁双层膜的物理性质显得非常重要,并已经成为当今凝聚态物理中的研究热点之一。鉴于磁性多层膜在物理研究和实际应用中的重大意义,本文选择“磁性多层膜系统的交换偏置、铁磁共振和自旋波性质的研究”作为研究课题。目前,实验上在铁磁/反铁磁多层膜系统中已经发现了很多有趣的物理现象同时也有多种方法用来探测其交换偏置等,其中最基本的方法是磁滞回线法,另外还有交流磁化法以及铁磁共振法等。其中铁磁共振法是获取磁晶各向异性以及磁弛豫等信息的主要手段,而磁弛豫等与外应力密切相关。同时实验还表明:铁磁/反铁磁双层膜系统中的交换偏置不仅和反铁磁材料的磁参量有关,而且和材料的微观结构也有很大的关系,如晶粒度、织构、界面粗糙度等。同时,样品的制备工艺和具体的生长条件对交换偏置影响也很大。本论文重点研究了外应力场存在的条件下,铁磁/反铁磁双层膜系统的交换偏置、铁磁共振和自旋波的性质。我们采用了自由能最小化的方法,研究了铁磁/反铁磁双层膜系统在外应力下的交换各向异性(交换偏置)和一致进动的自旋波性质(也就是铁磁共振现象)。本模型中铁磁层具有单轴磁晶各向异性和立方磁晶各向异性,而反铁磁层仅具有单轴磁晶各向异性,但其厚度趋于半无穷。理论上解析地给出了系统的等效交换更多还原

【Abstract】 There has been a great deal of interest in recent years in artificially engineered nano-structured materials with novel physical properties. One of particular interest is that of magnetic multilayers comprised of thin magnetic layers separated by thin non-ferromagnetic layers. They display some unusual physical properties, such as magnetic anisotropy, interlayer exchange coupling, giant magnetoresistance (GMR) and abnormal magneto-optical (MO) effect, and new applied prospects. The exchange bias effect, which arises from the interfacial exchange coupling between a ferromagnet (FM) and an antiferromagnet (AFM), was discovered more than 40 years ago. Recently, the effect has attracted much attention due to its application to giant magnetoresistive spin-valve heads for high-density recording systems. In order to understand the origin of this phenomenon, many experimental and theoretical results have been reported. In this thesis, the exchang bias, ferromagnetic resonanc and spin wave are studied.Recently many methods have been used to measure the exchange bias. The reversible measurement techniques, such as ac susceptibility and ferromagnetic resonance (FMR), other than the basic hysteresis loop measurement where the shift of loop corresponds to the exchange bias, have been used to determine the exchange anisotropy in exchange coupled bilayer systems. At the same time, many experimental results show that the characteristics of the exchange bias in FM/AFM bilayers not only depend on constituent of materials, but also on micro-structure of materials, such as size of particle, structure and rough of interface and so on. Meanwhile, the method and condition of growth of sample will affect the exchange bias.In this paper, we study the in-plane exchange anisotropy and spin wave (that is ferromagnetic resonance) in a ferromagnetic (FM)/antiferromagnetic (AFM) bilayer under stress field. Both cubic and uniaxial magnetocrystalline anisotropies are taken into account for the FM layer, while the AFM layer is only considered as uniaxial更多还原