1 August 1990 DC modulation noise in thin-film magnetic recording disk media
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DC Modulation noise was studied in thin film magnetic recording disk media as a function of magnetic layer thickness for plated, longitudinal, low-noise, 900 Oe to 1 100 Oe, Co-alloy disk media from a controlled fabrication runs. This noise is generated when a reverse longitudinal DC field is applied to a uniformly magnetized disk. This noise provides information on the uniformity of the disk for high density recording. Noise measurements using electronic detection via a spectrum analyzer provide resolution and sensitivity that is not obtainable from conventional microscopic observation. This noise was deduced to be caused by vanations in coercivity associated with defects in the medium, and not to surface roughness as has been conjectured previously. A new model was developed which allows autocorrelation functions and noise spectra to be calculated. The model agrees with measured spectral noise data with correlations greater than 0.99. The model treats the noise as effective transitions with an average magnetization less than saturation across the track width, an associated variance, and a linear distribution with Weibull process statistics, which generalizes previous work using the Poisson process for AC-erased noise. Data indicate that as the reverse field increases from zero, the distance between effective transitions peaks and then decreases as the field increases further. As the magnetic layer thickness increases from 25 nm to 60 nm, the maximum distance between effective transitions decreases from 2.8 im to 1 jim. The maximum average transition amplitude is bounded by 0.001 of the saturation magnetization and is independent of thickness.
© (1990) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Romney R. Katti, Romney R. Katti, Douglas A. Saunders, Douglas A. Saunders, } "DC modulation noise in thin-film magnetic recording disk media", Proc. SPIE 1248, Storage and Retrieval Systems and Applications, (1 August 1990); doi: 10.1117/12.19632; https://doi.org/10.1117/12.19632

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