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化的热力学和动力学参数（通过a1矩阵中L10相的成核和生长发生），通过测量热力学和动力学参数的测量，通过v，ti，au，ag或b的三元添加来提高对A1至L10转化的理解。 FEPT是硬盘驱动器（HDDS）开发磁性介质的领先候选人。自引入以来，薄膜技术已通过减小磁记录介质的厚度和记录位的尺寸来大大增加HDD的地面记录密度。但是，随着记录密度的增加，超级磁性构成基本限制的方法也会增加。结果，人们对与四方，L10晶体结构的Fept，Copt和相关的铁磁合金的兴趣越来越大。这些化学订购的四方合金具有最高的KU，除了含有稀土元件（例如SM）的KU，耐腐蚀性较差。 FEPT和COPT的各向异性比当今基于合金的媒体高20-40倍。当在室温下沉积（和COPT）合金膜时，形成了化学下来的面对面的立方体（FCC或A1）相。 A1相具有低磁晶的各向异性，因此不适合用作记录介质。形成L10阶段所需的退火时间和温度，即使是用比COPT更快的动力学，它与当前的媒体制造需求不相容，目前是在录制系统中实施这些合金的主要障碍。为了超越对降低（动力学）排序温度的合金进行工程的试验努力，对A1至L10转换的基本了解已成为必要。因此，如上所述，这些研究的目的是提高我们对具有三元合金添加的Fept膜中A1至L10转化的理解。工作的特殊重点将是合金添加的选择和数量对这些参数的影响。合金膜中转化的热力学和动力学参数（以及A1和L10相）的热力学参数将通过差分扫描量热法（DSC）来测量。除DSC外，X射线和电子衍射研究还将用于相位识别和确定远程阶参数，用于显微结构表征的透射电子显微镜以及用于胁迫测量的磁力测定法。非技术：除研究生研究外，该计划还将强烈支持本科研究；将竭尽全力使来自代表性不足的团体的学生参与；将支持PI实验室内的专门实验基础设施，材料科学和ENG部门的运营和维护。以及卡内基·梅隆（Carnegie Mellon）的数据存储系统中心（DSSC）；将确保学生参加专业社会的会议，并在DSSC的半年度会议上参加；将有助于开发商业技术，即HDDS的L10媒体。除了磁性记录介质外，还考虑了微磁性执行器和微型/纳米电机力学系统（MEMS/NEMS）中的其他元素的铁磁合金。这些系统的L10合金的形成类似地涉及从沉积的A1相转换。因此，这些研究也有望在这些组成部分的发展中受益。