Transition noise spectral measurements in thin film media

Noise in thin film media is concentrated at the transition center and must be characterized by a nonstationary autocorrelation function. The noise voltage spectrum is determined by the frequency response of this correlation function beyond the standard head field terms. In this work, the use of spectral measurement to determine the nonstationary noise is illustrated. Noise spectra of thin film media are experimentally studied in detail for various thin film disks using both inductive and MR heads. The results compare extremely well to the analytical expression of the spectrum derived utilizing a good approximation for the correlation function of the magnetization fluctuations. Both transition length and medium noise cross-track correlation width were determined from the measured spectra. The measured transition lengths agree with signal analysis, and the noise cross-track correlation widths range from 15 to 71 nm. Lowering the flying height reduces the transition widths, and the cross-track correlation width remains unchanged.>