Recording characteristics of perpendicular magnetic media with CoZrNb, NiFeNb, and exchange-pinned NiFeNb soft magnetic underlayers

Abstract

The recording performance of perpendicular media with amorphous CoZrNb, nanocrystalline NiFeNb, and exchange-pinned FeMn/NiFeNb soft magnetic underlayers ͑SULs͒ has been studied. A method has been proposed to quantify the spike noises from the SUL. We found that media with higher permeability NiFeNb SULs showed 4 db higher signal-to-noise ratio than media with lower permeability CoZrNb SULs. The exchange-pinned NiFeNb SUL suppresses spike noise and offers good recording performance. Furthermore, the recording frequency dependence of dynamic coercivity (H c ) was strongly affected by the use of different SULs. The increase in dynamic H c with linear density is negligibly small for media with NiFeNb SULs, whereas dynamic H c sharply increases with increasing density for media with CoZrNb SULs.

SNR improvement of granular perpendicular recording media

“…For example, simulation studies [5] show that if the permeability of the SUL is reduced to 100, the sensitivity to stray fields is greatly reduced, with little effect on recording performance. However, our experimental results [7] show that a higher permeability is preferable to achieving a better field gradient and, thus, improved SNR.…”

“…Unfortunately, most SUL materials are not only susceptible to stray fields causing random spike noises [4], but also deteriorate the recording performance. There remain discrepancies between theoretical simulations and experimental data on the effect of SUL permeability on recording performance [4]- [7]. For example, simulation studies [5] show that if the permeability of the SUL is reduced to 100, the sensitivity to stray fields is greatly reduced, with little effect on recording performance.…”

“…This method is simple, but it gives, at best, a qualitative representation. A more direct and quantitative method was proposed by counting the number of pulses whose amplitude exceeds a certain threshold [7]. Media performance comparison is done by rating the slope of the number of pulses versus voltage threshold curve.…”

“…For SUL spike noise evaluation, a method based on quantitatively counting the number of pulses whose amplitude exceeds a certain threshold is used [7]. Media performance comparison is done by ranking the pulse count at a fixed threshold level or by rating the slope of the number of pulses versus voltage threshold curve.…”