Remanent state noise in particulate magnetic recording media

Abstract

Remanent state noise is the variation in stray flux emanating from a magnetic recording medium which is in a remanent state of magnetisation. A portion of this noise is related to the magnetic microstructure of the recording medium. This study had two main objectives. The first was to devise and implement hard and software which was capable of capturing, storing and manipulating remanent state time series from a tape sample. The noise measurement apparatus was set-up to magnetise tape samples according to the principal remanent magnetisation curves.
A noise study, using commercially available products, was made to test the capabilities of the noise measurement system. In the majority of cases the noise was observed to follow 'typical' behaviours as described in the literature. However, a minority of samples displayed an interesting deviation in their noise behaviour which could be described as a superposition of the typical particle and cluster responses seen in past studies. It was also observed in some samples that the noise power would increase with number of passes. This effect was studied in-depth and the empirical evidence suggested that it was a phenomenon caused by inverse magnetostriction. The noise increase was observed in only selected samples based on cobalt modified gamma ferric oxide and chrome dioxide systems.
The second objective was to examine the remanent state noise characteristics of barium ferrite. This investigation involved examining samples produced from two different sources. (1) Tape samples have been produced 'in house' and such a set of
samples has been used to examine the relationship between milling, noise and particle interactions. The general trend that was observed was that increased milling led to a reduction in noise power. (2) Samples were also investigated from an industrial source.
These were used to test the relationship between noise, particle orientation and particle size. Contrary to the expected behaviour implied by past work, increased particle orientation (increasing measures of positive particle interactions) led to higher noise levels. However, decreasing particle size led to increasing measures of positive interactions and decreasing noise levels which had been predicted by previous studies.