Patterned magnetic thin films for ultra high density recording

The areal bit density of magnetic disk recording has increased since 1990 60% per year and even in the last years 100%. Extrapolation of these rates leads to recording parameters not likely to be achieved without changes in the present way of storing hard disk data. One of the possible solutions is the development of so-called patterned magnetic media. Such media will also shift the superparamagnetic limit positively in comparison with the present thin film media. Theoretically, a bit density in the order of Tbits/in 2 may be possible by using this so-called discrete magnetic recording scheme. The patterned structures presented in this paper consist of a regular two-dimensional array of single domain dots with large uniaxial magnetic anisotropy and have been prepared from CoNi/Pt multilayers with strong intergranular exchange coupling and large perpendicular magnetic anisotropy. For the preparation of the patterned media, a patterning process based on Laser Interference Lithography method (LIL) and Ion Beam Etching has been developed. This technology provides the possibility to pattern 2-D arrays of submicron dots smaller than the critical size for the transition from multi to single domain. The smallest prepared dot sizes are 60 nm with a center-to-center dot spacing of 200 nm and thickness of 30 nm. The magnetic characterization of these dots showed that they are single domain with reasonable coercivity and good thermal stability. Micromagnetic simulations show that the single domain state is the lowest energy state for dots with a diameter below 75nm, which confirms the experimental observations.