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

白色光刻构图薄膜磁介质提供了将磁数据存储介质的面位密度扩展可能两个数量级同时保持令人满意的信噪比特性的潜力。 目前的磁介质是由许多非常小的独立作用的单畴晶粒组成的连续的无特征薄膜形成的。 数据位的大小、形状和位置由写入磁头的磁场决定，每个位包含数千个晶粒。 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，从而产生了不可接受的“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于热激活磁化反转是不稳定的。 在这项研究中，磁结构和记录潜力的光刻图案化的纳米粒子阵列将进行研究。 在这样的介质中，每个纳米颗粒是单个域和单个数据位。 最初的研究将是外延钴薄膜，其中的晶体单轴各向异性应允许在平面内磁化的单域条形岛的合成，也平行于酒吧的短轴。 这种纳米颗粒阵列与目前的读写技术兼容。 将使用磁力显微镜和洛伦兹显微镜仔细检查孤立的单个纳米粒子的单域特性。 将确定阵列中磁化模式的稳定性，并测量阵列的信噪比特性。 为了摆脱外延膜固有的笛卡尔或六边形几何形状的限制，将合成适当磁化的棒状纳米颗粒，其在衬底上的取向可以是任意的（例如，磁盘上的径向或周向）。 所需的单轴各向异性将实现使用各向异性应变释放在一个条形纳米粒子，再加上磁致伸缩的材料。 非晶SmFe和SmCoFe家族的高磁致伸缩薄膜将探索用于此目的。 再次，单域字符，阵列的稳定性，和信号/噪声特性将进行评估。 ***

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. ***