The A1 to L1_0 Transformation in FePt Films with Ternary Alloying Additions

添加三元合金的 FePt 薄膜中 A1 到 L1_0 的转变

• 批准号: 0804765
• 负责人: Katayun Barmak
• 金额: $ 33万
• 依托单位: Carnegie-Mellon University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2008
• 资助国家: 美国
• 起止时间: 2008-07-01 至 2012-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0804765&HistoricalAwards=false
• 关键词: A1; L1_0; Transformation; FePt; Films

TECHNICAL: The objective of these studies is to improve our understanding of the A1 to L10 transformation in FePt with ternary additions of V, Ti, Au, Ag or B, through the measurement of thermodynamic and kinetic parameters of the transformation (which occurs by nucleation and growth of the L10 phase in the A1 matrix). FePt is the leading candidate for the development of magnetic recording media in hard disk drives (HDDs). Since its introduction, thin film technology has allowed large increases in areal recording densities of HDDs by decreasing the thickness of the magnetic recording medium and the dimensions of a recorded bit. However, as recording densities increase, so does the approach to the fundamental limit posed by superparamagnetism. As a result, there has been a growing interest in FePt, CoPt and related ferromagnetic alloys with the tetragonal, L10 crystal structure. These chemically-ordered tetragonal alloys have the highest known Ku except for those containing rare-earth elements such as Sm, which have poor corrosion resistance. The anisotropies for FePt and CoPt are 20-40 times higher than today's Co-alloy based media. When deposited at room temperature FePt (and CoPt) alloy films form the chemically-disordered face-centered cubic (fcc, or A1) phase. The A1 phase has low magnetocrystalline anisotropy and is consequently unsuitable for use as a recording medium. The annealing times and temperatures needed to form the L10 phase, even for FePt with its faster kinetics than CoPt, are incompatible with current media manufacturing needs, and, at present, are major barriers to the implementation of these alloys in recording systems. To move beyond a trial-and-error effort of engineering the alloys for reduced (kinetic) ordering temperature, a deeper fundamental understanding of the A1 to L10 transformation has become necessary. Thus, as noted above, the objective of these studies is to improve our understanding of the A1 to L10 transformation in FePt films with ternary alloying additions. The particular emphasis of the work will be the impact of the choice and quantity of alloying additions on these parameters. The thermodynamic and kinetic parameters of the transformation (and the Curie temperature of the A1 and L10 phases) in alloy films will be measured by differential scanning calorimetry (DSC). In addition to DSC, x-ray and electron diffraction studies will be used for phase identification and determination of the long-range order parameter, transmission electron microscopy for microstructure characterization, and magnetometry for coercivity measurements. NON-TECHNICAL: The program will strongly support undergraduate research in addition to graduate research; will make an extensive effort to involve students from underrepresented groups; will support the operation and maintenance of the specialized experimental infrastructure within the PI?s laboratories, the Dept. of Materials Science and Eng. and the Data Storage Systems Center (DSSC) at Carnegie Mellon; will ensure student participation at meetings of professional societies, and in the semi-annual meetings of the DSSC; will help the development of commercial technology, namely, L10 media for HDDs. In addition to magnetic recording media, ferromagnetic L10 alloys are being considered for magnetic actuators and other elements in micro/nano-electromechanical systems (MEMS/NEMS). The formation of L10 alloys for these systems similarly involves transformation from a deposited A1 phase. Therefore, these studies are also expected to be of benefit in the development of these components.

技术：这些研究的目的是通过测量转变的热力学和动力学参数（通过A1基体中L10相的成核和生长发生），提高我们对三元添加V、Ti、Au、Ag或B的FePt中A1到L10转变的理解。FePt是硬盘驱动器（hdd）中磁性记录介质发展的主要候选材料。自推出以来，薄膜技术通过减少磁性记录介质的厚度和记录钻头的尺寸，大大增加了hdd的面记录密度。然而，随着记录密度的增加，超顺磁性所构成的基本极限的接近也在增加。因此，人们对FePt， CoPt和相关的具有四方L10晶体结构的铁磁合金越来越感兴趣。除了含有稀土元素（如Sm）的合金具有较差的耐腐蚀性外，这些化学有序的四方合金具有已知的最高Ku。FePt和CoPt的各向异性比目前的Co-alloy基介质高20-40倍。室温沉积时，FePt（和CoPt）合金薄膜形成化学无序的面心立方相（fcc，或A1）。A1相具有低磁晶各向异性，因此不适合用作记录介质。形成L10相所需的退火时间和温度，即使对于FePt具有比CoPt更快的动力学，也与当前的介质制造需求不相容，并且目前是这些合金在记录系统中实现的主要障碍。为了超越在降低（动力学）有序温度下设计合金的试错努力，有必要对A1到L10转变有更深入的基本了解。因此，如上所述，这些研究的目的是提高我们对添加三元合金的FePt薄膜中A1到L10转变的理解。工作的重点将是合金添加量的选择和数量对这些参数的影响。采用差示扫描量热法（DSC）测量合金膜中相变的热力学和动力学参数（以及A1和L10相的居里温度）。除DSC外，x射线和电子衍射研究将用于相识别和确定长程有序参数，透射电子显微镜用于微观结构表征，磁强计用于矫顽力测量。非技术：除了研究生研究外，该计划还将大力支持本科生研究；将作出广泛努力，让来自代表性不足群体的学生参与进来；将支持PI内专业实验基础设施的操作和维护？材料科学与工程系。卡内基梅隆大学的数据存储系统中心（DSSC）；确保学生参加专业学会的会议，以及社会科学委员会的半年度会议；将有助于商用技术的发展，即hdd的L10介质。除了磁性记录介质外，铁磁性L10合金还被考虑用于微/纳米机电系统（MEMS/NEMS）中的磁致动器和其他元件。这些体系的L10合金的形成同样涉及沉积的A1相的转变。因此，这些研究也有望对这些成分的开发有益。