Magnetic correlations in ac erased media: A contribution to tape noise

A study has been made of the noise power spectral density P(k) of ac erased recording media using a model based on the simulated annealing technique. The P(k) produced show a consistent trend with the rate of ac demagnetisation. The noise (for predominantly negative interactions) is found to decrease with decreasing rate of reduction, corresponding to an increase of the degree of correlation which arises from interparticle interactions. In terms of the annealing analogy the system is allowed to approach equilibrium at lower demagnetisation rates, which allows the correlation to develop. The implications for the modelling of the noise from recording media are discussed.