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Thermally activated magnetization reversal processes in longitudinal magnetic recording media are the origin of signal decay and time dependence of the coercivity. The former may limit the lifetime of the stored data and the latter determines the minimal write fields at short pulse widths. Both effects depend on the ratio of the reversal barrier and the thermal energy. Signal decay and time dependent coercivity measurements are combined in this paper to experimentally derive a stability ratio, 1/C, as a function of film thickness, recording density and temperature. The experiments are performed with a contact write/read tester using a merged read/write head in physical contact with the sample. Samples are mounted on a variable temperature stage (300 - 390 K) allowing to vary the stability ratios. The samples are a series of CoPtCr recording media with thicknesses from 5.5 nm to 13.0 nm. In the low density limit (500 fc/mm) the onset of thermal decay is observed near [(1/C).sub.0] [approximately equals] 38. Keywords--Magnetic viscosity, magnetic recording, time-dependent coercivity, superparamagnetism.

A study of a series of progressively aligned metal particle tape samples has been undertaken. Our data indicates that increasing the orientation, desirable for better recording performance, has been found to increase thermal effects at both DC and high frequencies. The implications of this are that larger head fields are required to write high frequency transitions on more aligned media. The experimental results are compared to the switching model suggested by el Hilo to determine the thermal stability factor [KV.sub.m]/kT of the samples. Index Terms--interactions, magnetisation reversal, metal particles, orientation, pulsed magnetic fields, thermal stability

A self-consistent recording simulator combined with a micromagnetic MR head model is developed to study write equalization in tape recording. The simulation study presented in this paper focuses on the understanding of the magnetization configurations resulted from write equalization and the impact on the write and read nonlinearity. It is found that the write equalization process results in a demagnetized state in otherwise saturated regions. The model analysis combined with an EPR4 channel demonstrates how both write and read linearity of the system are improved. Index Terms--write equalization, tape recording, nonlinearity.

To explain the origin of noise in a perpendicular magnetic recording medium, the surface-nucleation model which assumes weak anisotropy on the surface layers is utilized. The model shows that DC-erased noise results from tilting magnetization in the film. The tilting angle is increased by the existence of weak anisotropy on the surface layers. The surface layers with weak anisotropy trigger the magnetization reversal of the whole film and enhance thermal fluctuations. As a result, coercivity at a finite temperature decreases dramatically. It is concluded that control the magnetic properties on the medium surface is very important in order to attain low noise and stability against thermal fluctuation. Index Terms--computer simulation, medium noise model, perpendicular magnetic recording, thermal fluctuation