Magnetic time effects in small metallic particles for recording: orientation dependence

The leading magnetic material for use in data recording tapes is the metal particulate (MP) composition. The trend to smaller particle size necessarily entails an increase in thermally induced time effects. An Arrhenius-Ne´el switching model is used, together with the dependence of the experimental coercivity on field duration, to determine an effective switching volume. The model takes account of the highly imperfect magnetic orientation present in actual recording media. Results for coated media made with current advanced particles having various degrees of orientation (squareness) show that the calculated switching volume is not sensitive to orientation above a squareness value of about 0.6 (essentially random in plane). This switching volume correlates well with particle volume, as determined by transmission electron microscopy (TEM). These results confirm the practical relevance of the model, both for realistic tapes and for disks that have random grain orientation, and are evidence that the model adequately takes account of preferred-axis misalignment.