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

技术支持：这些研究的目的是提高我们的理解的A1到L10的转变FePt与三元添加V，Ti，Au，Ag或B，通过测量的热力学和动力学参数的转变（发生在A1矩阵的L10相的成核和生长）。FePt是开发硬盘驱动器（HDD）中磁记录介质的主要候选材料。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位的尺寸，薄膜技术已经允许HDD的面记录密度的大幅增加。然而，随着记录密度的增加，超顺磁性所造成的基本极限也越来越接近。因此，人们对具有四方晶系L10晶体结构的FePt、CoPt和相关铁磁合金越来越感兴趣。这些化学有序的四元合金具有已知的最高Ku，除了那些含有稀土元素如Sm的合金，它们具有较差的耐腐蚀性。FePt和CoPt的各向异性比目前的钴合金基介质高20-40倍。当在室温下沉积时，FePt（和CoPt）合金膜形成化学无序的面心立方（fcc，或A1）相。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，即使对于具有比CoPt更快的动力学的FePt，也与当前的介质制造需求不相容，并且目前是在记录系统中实现这些合金的主要障碍。为了超越设计合金以降低（动力学）有序温度的试错努力，有必要对A1到L10转变进行更深入的基本理解。因此，如上所述，这些研究的目的是提高我们的理解的A1到L10的转变FePt膜与三元合金添加。特别强调的工作将是这些参数的合金添加剂的选择和数量的影响。用差示扫描量热法（DSC）测定了合金薄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）。除了DSC，X-射线和电子衍射研究将用于相鉴定和确定的长程有序参数，透射电子显微镜的微观结构表征，和磁力测量的磁性测量。非技术性：该计划将大力支持本科研究，除了研究生研究;将作出广泛的努力，让学生从代表性不足的群体;将支持PI内的专业实验基础设施的运行和维护？的实验室，该部门。材料科学与工程学院和卡内基梅隆大学的数据存储系统中心（DSSC）;将确保学生参加专业协会的会议和DSSC的半年度会议;将帮助开发商业技术，即用于HDD的L10介质。除了磁记录介质之外，铁磁L10合金正在被考虑用于微/纳机电系统（MEMS/NEMS）中的磁致动器和其他元件。这些系统的L10合金的形成类似地涉及从沉积的A1相的转变。因此，预计这些研究也将有利于这些组件的开发。

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.