Model of media noise generation based on modulation theory

Abstract

A random profile of transitions in magnetization on thin-film media causes fluctuations of transition-region widths and locations. The readback transducer reacts to an averaged derivative of magnetization, and this results in modulation of magnetization derivative pulses, in shape and amplitude as well as in position (jitter). Due to bandwidth limitations in the readback transducer the high-frequency sideband of the modulation is almost totally suppressed. Thus, readback filtration converts a double-sideband write-cycle modulation into a single-sideband readback modulation.

Recent advances in the recording physics of thin-film media

“…This formula represents an approximation of the behaviour of the entire grain assembly. As pointed out in [78] exchange interaction between the grains reduces the prefactor (0.566) that appears in equation (64). Typical media have weak exchange coupling and for h e = 0.05, the prefactor is 0.474 [78].…”

“…Since the noise increases with linear density, it was concluded, early on, that the noise must be associated with the transitions themselves. Transition noise has been treated theoretically in a number of papers [37,[46][47][48][49][50][51][52][53][54][55][56][57][58][59][60][61][62][63][64]. Overviews of simulation work can be found in [14,15].…”

“…Gaussian white noise associated with a resistor. As Minhuin points out [64], the noise-while being an additive noise to the medium magnetization-is multiplicative in nature at read back, and therefore appears as modulation noise. Since the read-back process represents a band-pass filter with a well defined shape, the modulation side bands are subjected to the filtering process.…”

“…Equation (64) was derived for media with no distribution of grain sizes. Real media, however, have grain size distributions.…”

“…Typically, the grain size distribution function is log-normal, as sketched in figure 17. It can be shown that the functional dependence of equation (64) does not change when a grain size distribution is considered.…”