Lithographically Formed Nanoparticles for an Ultra High Density, Low Noise, Magnetic Data Storage Medium

9710395白色光刻图像化薄膜磁性介质提供了在保持令人满意的信噪特性的同时将磁性数据存储介质的面位密度可能扩展两个数量级的潜力。目前的磁性介质是由许多非常小的独立作用的单畴晶粒组成的连续无特征薄膜。数据位的大小、形状和位置由写入磁头的磁场决定，每个位包含数千个颗粒。随着数据密度越来越高，比特大小越来越小，介质的粒度变得很麻烦，产生了不可接受的“介质噪声”。原则上可以通过减小晶粒尺寸来降低噪声，但是比目前使用的小得多的晶粒对热激活磁化反转是不稳定的。在这项研究中，将研究光刻图像化纳米颗粒阵列的磁性结构和记录电位。在这样的介质中，每个纳米粒子是一个单一的域和一个单一的数据位。最初的研究将是在外延钴薄膜上，其中晶体的单轴各向异性应该允许合成平面磁化的单畴条形岛屿，也平行于条形的短轴。这种纳米粒子阵列与现有的读写技术兼容。孤立的单个纳米颗粒的单畴特性将使用磁力显微镜和洛伦兹显微镜仔细检查。将确定阵列中磁化模式的稳定性，并测量阵列的信噪特性。为了避免外延膜固有的笛卡尔或六边形几何结构的限制，将合成适当磁化的条形纳米颗粒，其在衬底上的方向可以是任意的（例如，在圆盘上的径向或周向）。所需的单轴各向异性将通过棒状纳米颗粒中的各向异性应变释放来实现，再加上材料的磁致伸缩。本文将探讨高磁致伸缩薄膜的非晶SmFe和SmCoFe族。再次，将评估单域特性，阵列稳定性和信号/噪声特性。＊＊＊

9710395 White Lithographically patterned thin film magnetic media offer the potential for extending the areal bit density of magnetic data storage media perhaps two orders of magnitude while preserving satisfactory signal-to-noise properties. Present magnetic media are formed of a continuous featureless thin film comprised of many very small independently acting single-domain grains. The size, shape, and position of the data bit is determined by the magnetic fields from the write head and each bit contains thousands of grains. As data densities get higher, and bit size smaller, the granularity of the medium has become troublesome, giving rise to unacceptable "media noise". In principle the noise could be reduced by decreasing grain size, but grains much smaller than are presently in use are unstable against thermally activated magnetization reversal. In this study, the magnetic structure and recording potential of lithographically patterned nanoparticle arrays will be studied. In such a medium, each nanoparticle is a single domain and a single data bit. The initial studies will be on epitaxial cobalt thin films, where the crystalline uniaxial anisotropy should allow the synthesis of single-domain bar shaped islands magnetized in plane and also parallel to the short axis of the bar. Such a nanoparticle array is compatible with present read-write technology. The single-domain character of isolated individual nanoparticles will be carefully examined using magnetic force microscopy and Lorentz microscopy. The stability of the magnetization pattern in an array will be determined, and the signal-to-noise characteristics of an array measured. To escape the restriction to a Cartesian or hexagonal geometry inherent in the epitaxial films, synthesis will be pursued of appropriately magnetized bar-shaped nanoparticles whose orientation on the substrate can be arbitrary (radial or circumferential on a disk, for instance). The required uniaxial anisotropy will be achieved using the anisotro pic strain relief in a bar-shaped nanoparticle, coupled with the magnetostriction of the material. The amorphous SmFe and SmCoFe family of highly magnetostrictive films will be explored for this purpose. Again, single domain character, array stability, and signal/noise characteristics will be evaluated. ***