Magnetisation reversal studies of particulate recording media
Both an experimental investigation of the interaction effects within commercial particulate recording media and a numerical investigation of the reversal mechanism of particles within the media have been made. The particle systems investigated comprised three audio y-Fe203 tapes, three audio Cr02 tapes and a video metal particle tape. An absolute measure of the interaction effects within particulate tapes has been investigated by comparing the measured properties of isolated particles taken from the medium with the measured bulk properties of the medium. The results indicated negative interactions for all the samples investigated except the video metal particle tape, which indicated positive interactions. However, Al plots for all the samples however, indicated negative interactions. This is contrary to the absolute interactions measured in the video metal particle tape. A possible explanation for this inconsistency was the presence of highly localised alignment of particles, "a chaining effect", within the metal particle system. This effect allows for increased system coercivity without removing the general negative interactions characteristic of all acicular particulate media. A micromagnetic model was developed to study typical y-Fe203 and Cr02 particles measured experimentally in this study. Simulations were performed as a function of the applied field angle and the results compared to the experimental study. The simulations representing typical 'y-Fe203 particles indicated reasonable agreement at the lower applied field angles, while poorer agreement was observed at larger applied field angles. The simulations representing a typical Cr02 particle indicated reasonable agreement at the higher applied field angles, while poorer agreement was observed at low applied field angles. These inconsistencies for both types of particles investigated were accounted for by assumptions and simplifications within the model, particularly the absence of bulk crystalline imperfections, the degree of surface irregularities and the effect of an oversimplified particle shape. The micromagnetic model developed was also used to investigate the effect of model parameters on the reversal mechanism of the 'y-Fe203 particle simulation. It was found that the reversal mechanism was very sensitive to the size and shape of the model particle.