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。数据存储行业的主导分支是磁硬盘驱动器。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。超顺磁性响应是指磁性纳米粒子的磁矩在热激活时发生切换，从而导致记录信息丢失的可能性。如果没有被增加的记录介质的磁晶各向异性能量密度平衡，则对于较小的比特大小，开关频率变得更大。事实上，达到1 TB/in2或更高的存储密度的关键(记录介质)限制是超顺磁性造成的。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。当在室温下沉积时，FePT和CoPT合金薄膜形成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。为了获得化学有序的L10结构，需要在高温(600摄氏度)下进行沉积后处理或在加热的衬底上沉积(500摄氏度)。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。为了超越为降低有序温度而设计合金的反复尝试的努力，有必要对A1到L10转变有更深的基本理解。因此，这些研究的目的是通过测量A1到L10转变的热力学和动力学参数，加深对FePT、CoPt和相关的三元(FeCuPT，FeNiPT)合金薄膜中A1到L10转变的理解。本研究的重点是合金化学和成分对这些参数的影响。用差示扫描量热法(DSC)测量了L10合金在均匀的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研究将随着DSC对元素多层膜中L10相形成的研究的补充，这些多层膜包括Fe和铂(Fe/Pt)和Co和铂(Co/Pt)。除了DSC，X射线和电子衍射研究还将用于物相鉴定和长程有序参数测量，以及用于表征薄膜微结构的透射电子显微镜研究。更广泛的影响：该计划(I)除了研究生研究外，还将大力支持本科生研究；(Ii)将做出广泛努力，让代表人数不足的群体的学生参与进来；(Iii)将支持PI实验室--系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；(4)将帮助开发商业技术，即用于硬盘驱动器的L10介质，预计存储容量为1 TB/in2及以上。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。用于这些系统的L10合金的形成类似地涉及真空沉积的Al相的转变。因此，预计拟议的研究也将有助于这些组成部分的发展。

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.