Effects of magnetic layer thickness and of head-to-medium spacing on noise in advanced particulate recording media

Abstract

The effects of magnetic layer thickness on the noise characteristics of advanced metal particle tape have been observed using a dc demagnetization process generated with a uniform in-plane magnetizer. The three-dimensional (3D) surface maps of spectral noise power plotted as a function of remanent magnetization state showed a change in behavior as the recording layer became thinner. The thickest magnetic coating of 310 nm showed “trough-like” characteristics associated with conventional thick particulate media. The thinnest sample with a 165 nm magnetic coating showed a “peak-like” response that is observed in continuous thin-film media, with a graduated trend from one to the other for the two intermediate samples. A simulation of these results has been made with an 8000 spherical particle micromagnetic model of the media remanent states and a simulated magnetoresistive read head. Noise maps produced from the simulation compared well with experiment. Spatial isolation of the noise contributions was achieved by dividing the modeled magnetic layer into sublayers. This revealed that particles at the surface were the source of the “peak-like” response, and their contributions became more dominant as the magnetic coating got thinner. Further model investigations showed an association of the different sublayer characteristics with a change in the mean magnetostatic interaction field. The interaction field of particles at the surface had characteristics similar to those of 2D granular thin films and hence generated “thin film-like” noise. A further effect was associated with the spacing between the head and various regions of particles. As this was increased, not only was the amplitude of the noise reduced, but the increased region of integration meant that longer range correlations were incorporated into the observed characteristics, resulting in noise maps more like those of conventional thick particulate media.