The A1 to L1o Transformation in FePt, CoPt and Related Ternary Alloy Films

技术优势：数据存储是信息革命的一个极其重要的组成部分。数据存储行业的主要分支是磁性硬盘驱动器。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。超顺磁响应是指磁性纳米颗粒磁矩的热激活切换的概率，其结果是记录信息的丢失。如果不通过记录介质的增加的磁晶各向异性能量密度来抵消，则对于较小的比特尺寸，切换频率变得更大。事实上，达到1 Tb/in 2及以上的存储密度的关键（记录介质）限制是由超顺磁性造成的。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。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。在高温（600摄氏度）下的沉积后退火或在加热的衬底上的沉积（500摄氏度）对于实现化学有序的L10结构是必要的。这种高温处理步骤与介质制造需求不相容，并且目前是在记录系统中实施这些合金的主要障碍。为了超越设计合金以降低有序温度的试错努力，有必要对A1到L10转变有更深入的基本理解。因此，这些研究的目的是提高理解的A1到L10的转变FePt，CoPt和相关的三元（FeCuPt，FeNiPt）合金薄膜，通过测量的热力学和动力学参数的转变。本研究的一个特别重点是合金化学和成分对这些参数的影响。采用差示扫描量热法（DSC）测量了均匀二元和三元合金薄膜中相变的热力学和动力学参数（以及L10合金的居里温度）。这些合金的DSC研究将增加与DSC研究的形成的L10相的元素多层膜的Fe和Pt（Fe/Pt）和Co和Pt（Co/Pt）。除了DSC，X-射线和电子衍射研究将用于相鉴定和远程序参数测量，和透射电子显微镜研究薄膜微观结构的表征。更广泛的影响：该计划（i）将大力支持本科研究，除了研究生研究;（ii）将作出广泛的努力，让学生从代表性不足的群体;（iii）将支持PI的实验室，部门内的专业实验基础设施的操作和维护。（iv）将帮助开发商业技术，即用于预计存储容量为1 Tb/in 2及以上的硬盘驱动器的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真空沉积的A1相的转变。因此，预计拟议的研究也将有利于这些组件的开发。

Technical Merit: Data storage is an extremely important component of the information revolution. The dominant branch of the data storage industry is the magnetic hard disk drive. As recording densities increase, so does the approach to the fundamental limit posed by superparamagnetism. Superparamagnetic response refers to the probability of thermally activated switching of magnetic nanoparticle moments with consequent loss of recorded information. The switching frequency becomes larger for a smaller bit size, if not counterbalanced by an increased magnetocrystalline anisotropy energy density of the recording medium. Indeed, the critical (recording medium) limitation in reaching storage densities of 1 Tb/in2 and beyond is that 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. 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. Post-deposition annealing at high temperatures ( 600 degrees C) or deposition on heated substrates ( 500 degrees C) is necessary to achieve the chemically ordered L10 structure. Such high-temperature processing steps are incompatible with 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 ordering temperature, a deeper fundamental understanding of the A1 to L10 transformation is necessary. Thus, the objective of these studies is to improve understanding of the A1 to L10 transformation in FePt, CoPt and related ternary (FeCuPt, FeNiPt) alloy films, through the measurement of thermodynamic and kinetic parameters of the transformation. A particular emphasis of this research is the effect of alloy chemistry and composition on these parameters. The thermodynamic and kinetic parameters of the transformation (and the Curie temperature of the L10 alloy) in homogeneous binary and ternary alloy films will be measured by differential scanning calorimetry (DSC). The DSC studies of these alloys will be augmented with DSC studies of the formation of the L10 phase in elemental multilayer films of Fe and Pt (Fe/Pt) and Co and Pt (Co/Pt). In addition to DSC, x-ray and electron diffraction studies will be used for phase identification and long-range order parameter measurement, and transmission electron microscopy investigations for characterization of film microstructure. Broader Impact: The program (i) will strongly support undergraduate research in addition to graduate research; (ii) will make an extensive effort to involve students from underrepresented groups; (iii) 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; (iv) will help the development of commercial technology, namely, L10 media for hard disk drives with projected storage capacities of 1 Tb/in2 and beyond. 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 vacuum-deposited A1 phase. Thus, the proposed studies are also expected to be of benefit in the development of these components.