Dynamic response and noise of recording media

Abstract

A study of medium noise and Neutron Depolarisation in recording media has been made as a function of remanent magnetisation along the isothermal remanence and dc demagnetisation remanence curves. The measurements are discussed in relation to VSM measurements of the remanent characteristics. Medium noise measurements are presented for commercial particulate media, experimental barium ferrite media and commercial metal evaporated thin film media, while Neutron Depolarisation measurements are presented for commercial particulate media alone.
The results show that medium noise is not a unique function of magnetisation, but is also dependent upon the magnetic rnicrostructure brought about through its magnetic history; a microstructure which is in turn also dependent upon the
physical microstructure. This is seen through asymmetry in the observed noise during dc demagnetisation, and also in observed differences in noise between the two remanence curves In particular, a distinct difference is seen between the dc erased and ac erased states, where efficient flux closure and lower energy configurations are attributing factors to the lower ac erased noise. An effect which is also supported by Neutron Depolarisation results in these states.
Through the choice of samples with distinctly different physical microstructures within each media type studied, the medium noise measurements show how important a role the physical rnicrostructure has in its effect on the magnetic microstructure,
illustrating that the sensitivity of medium noise measurements as a natural probe of the magnetic and physical microstructures is an important source of information towards the general characterisation and understanding of magnetic
recording materials.