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Abstract
Current high-density magnetic recording systems utilize magnetoresistive (MR) playback heads and polycrystalline thin film media. In this dissertation, several key problems in such systems are studied both experimentally and theoretically.
Playback characteristics of MR heads are studied using a linear theory. A simple model is developed to derive analytical expressions for the longitudinal surface fields from several types of MR heads. Analytical formulas for PW 50, D50 and peak playback voltage are also obtained. These results are useful for analyzing the effect of recording geometry on playback properties.
A theoretical study of nonlinear transition shift is conducted. An analytical formula for nonlinear transition shift is derived and utilized to study the dependence of nonlinear transition shift on recording parameters. The write precompensation levels for transitions in a series are calculated.
Thermal stability of recorded bits in thin film media consisting of small grains is studied. This issue is crucial to the development of longitudinal media for ultra-high density recording. An experimental technique is developed to accurately measure the time dependence of playback signal amplitude and noise level due to the decay of recorded magnetization patterns. This technique is applied to a systematic investigation of the dependence of signal and noise decay on recording density and magnetic layer thickness in longitudinal thin film media. A NEel-Arrhenius type model is developed to calculate the time evolution of a square wave magnetization transition pattern subject to thermal agitation. Further, noise decay is calculated based on the magnetization decay results through a simplified model. The calculation results of signal and noise degradation with time agree well with the measurement data.
