Co基合金超薄膜的结构与磁性

【作者】 许晓英；

【导师】 金晓峰；

【作者基本信息】 复旦大学 ， 凝聚态物理， 2008， 博士

【摘要】 近年来,结合电子电荷与自旋的自旋电子学与自旋电子学元件因为其广泛的应用前景而引起了人们极大的研究兴趣。薄膜磁学是其中一个重要的分支。随着尺度降低到纳米量级,许多新奇的物理现象出现。而新的样品制备技术和高灵敏度的磁性测量手段也使研究超薄膜的磁性成为可能。本人在博士期间的工作及结果主要包括以下四个方面：1研究了自然界中不存在的体心立方结构(bcc) Co的磁晶各向异性以及Co/GaAs(001)体系结构与磁性的关联。随Co膜厚度增加体系发生结构相变,磁性也随之变化。通过改变生长温度调节了结构相变发生的位置。同时也排除了六角密堆积结构(hcp)Co对bcc Co磁性的影响,定量的给出bcc Co的磁晶各向异性常数,合理地解释了以往关于bcc Co磁性的实验事实。2系统地研究了在GaAs(001)上生长的bcc FexCo1-x合金薄膜结构与磁性的关联以及在GaAs衬底上单轴各向异性的起源。立方晶系的结构并不能决定磁晶各向异性的易轴方向。对于同样为bcc结构的FexCo1-x合金,其磁晶各向异性的易轴随Fe成分由<100>方向转向<110>方向。通过改变FexCo1-x合金成分,半导体衬底(GaAs)与金属薄膜之间的晶格失配得以改变,进而实现了对单轴各向异性的调节。3系统地研究了面心立方结构(fcc)的CoxPd1-x合金薄膜的磁性以及CoxPd1-x合金薄膜垂直各向异性的起源。薄膜合金的磁各向异性易轴随Pd成分的增多由CoxPd1-x<110>方向转到<100>方向,转变点在Co0.5Pd0.5。通过改变缓冲层(Cu和Au)来调节Co0.25Pd0.75薄膜是否具有垂直各向异性。4研究了亚原子层Mn/Fe双层膜体系中Mn和Fe之间的耦合情况。C(2×2)的Mn降低了整个体系的铁磁性,同时居里温度降低。这来源于Fe和Mn之间的反铁磁耦合,以及Mn和Mn之间反铁磁的耦合作用。更多还原

【Abstract】 In the recent decades, spintronics and spintronic devices which combine electron charge and spin attract scientists’interest greatly for their potential industrial applications. Thin film magnetism is one of the important research areas. With the decreasing dimensionality, especially to the nanometer scale, brand new phenomena emerges. In the mean time, new technologies for sample preparation and new equipments for magnetic measurement with high sensitivity make it possible to investigate and manipulate the magnetic properties of ultrathin films.Some of my works are listed as follows:1 The magnetocrystalline anisotropy of body-centered-cubic(bcc) Co, which does not exist in nature, is investigated. The crystalline structure and magnetic properties of Co/GaAs(001) are also exploited. With the increasing Co thickness, there is a structural phase transition:from body centered cubic (bcc) to hexagonal close packed (hcp) structure. The critical thickness depends on the growth temperature of Co. The magnetocrystalline anisotropy constants of bcc Co is quantitatively determined by excluding the magnetic effects from hep Co, which consists with all the previous experiments results.2 The correlation between magnetic properties and crystalline structure of bcc FexCo1-x flims and the origin of uniaxial anisotropy are studied. Bcc cubic symmetry does not necessarily require the easy axes of magnetocrystalline anisotropy parallel to <100> directions, which switch from bcc FexCo1-x<100> to<110> directions from Fe rich end to Co rich end. The misfit between GaAs substrate and FexCo1-x films, which could be tuned by Fe composition, manipulates the orientation of easy axis of uniaxial anisotropy.3 The magnetic properties of face-centered-cubic (fcc) CoxPd1-x films and the origin of perpendicular magnetic anisotropy are studied. The easy axes of magnetocrystalline anisotropy are found to switch from<110> to<100> directions, which is different from those of bulk alloys. The transition point is at 50% Co. The possession of perpendicular magnetic anisotropy in films depends on the buffer layer(Au or Cu).4 Submonolayer Mn/Fe/Cu(001) was investigated on the interaction between Mn and Fe. The magnetization and Curie temperature of the whole system are lowered. Mn is found to be antiferromagnetically coupled to Fe and the interaction between Mn更多还原