ac demagnetization of particulate and thin film recording media

ac demagnetization processes have been investigated for different starting remanence states and compared to dc demagnetization processes. Measurements have been made in a range of magnetic recording media including acicular p articulate flexible media, Ba-ferrite coatings and sputtered thin films. In all cases an offset of the ac demagnetization relative to that expected fr om dc measurements was observed, which could be to higher or lower fields. This could not be explained in terms of expected trends from interaction ef fects or time dependence and additional processes had to be invoked. (C) 20 00 American Institute of Physics. [S0021-8979(00)39008-9].