Percolation studies in synthetic ferrimagnetic recording media

We have studied the percolation limit of synthetic ferrimagnetic media (SFM) by the measurement of noise power and third harmonic ratio and by imaging with a high-resolution magnetic force microscope (MFM). The noise power spectrum, which helps to find the onset of percolation, is significantly different in SFM structures compared to the conventional recording media. Properties of the stabilization layers, such as switching field distribution (SFD), are highly influential in deciding the integrated noise power spectrum. With suitable selection of high moment stabilization layers, the noise at higher densities, within the percolation density limit, can be substantially reduced. Third harmonic ratio studies indicate that the partial erasure occurs above ∼900 kfci. Using a high-resolution high-Q MFM, it is possible to obtain stable and nonpercolating high density patterns up to 1000 kfci on media with tBr=0.22 memu/cm² and Hc∼4500 Oe. This results in practical designs of media for recording densities >150 Gbits/in².