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基质中L10相的形核和生长)，提高我们对V、Ti、Au、Ag或B三元添加的FePT中A1到L10转变的理解。FePT是开发硬盘驱动器(HDD)中的磁记录介质的领先候选者。自从引入薄膜技术以来，通过减小磁记录介质的厚度和记录比特的尺寸，使得HDD的面记录密度大幅增加。然而，随着记录密度的增加，接近超顺磁性所构成的基本极限的程度也在增加。因此，人们对具有四方L10晶体结构的FePT、CoPt及相关铁磁合金的兴趣与日俱增。这些化学有序的四方合金具有最高的Ku，除了那些含有稀土元素的合金，如Sm，这些元素的耐腐蚀性很差。FePT和CoPt的各向异性比今天的钴合金介质高20-40倍。当在室温下沉积时，FePT(和CoPT)合金薄膜形成了化学无序的面心立方(FCC，或A1)相。A1相具有低的磁晶各向异性，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，即使对于其动力学速度比CoPT快的FePT，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施的主要障碍。为了超越为降低(动力学)有序温度而设计合金的反复尝试的努力，有必要对A1到L10转变有更深的基础理解。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化的FePT薄膜中A1到L10转变的理解。这项工作的重点将是合金添加的选择和数量对这些参数的影响。用差示扫描量热法(DSC)测量了合金薄膜的热力学和动力学参数(A1相和L10相的居里温度)。除了DSC，X射线和电子衍射研究将被用于物相鉴定和长程有序参数的确定，透射电子显微镜用于微结构表征，以及磁测量用于矫顽力测量。非技术性：除了研究生研究外，该计划还将大力支持本科生的研究；将做出广泛努力，让代表不足的群体的学生参与进来；将支持皮埃尔？S实验室内专业实验基础设施的运营和维护。材料科学与工程系。和卡内基梅隆大学的数据存储系统中心；将确保学生参加专业学会的会议和数据存储系统中心的半年一次的会议；将有助于商业技术的发展，即硬盘驱动器的L10介质。除了磁记录介质外，铁磁性L10合金也被考虑用作微/纳米机电系统(MEMS/NEMS)中的磁致动器和其他元件。对于这些系统，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组成部分的开发有所裨益。