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

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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. ***