Measurement of interaction fields in particulate tapes by linearization of the Henkel plot

Inter-particle interactions are a major source of noise in particulate recording media and, as such, impose limits on recoding densities. It is well-established that these interactions may be studied by isothermal (I
_r
) and dc demagnetization (I
_D
) remanence measurements. Such measurements are usually analyzed using Henkel plots or the more recently introduced δ-I plots. In the absence of interactions, Wohlfarth's theory predicts that I
_D
= 1 – 2I
_r
. Clearly, an experimental (Henkel) plot of I versus I results in a straight line of slope -2 for a non- interacting dispersion. In reality, the Henkel plot in the vast majority of commercial tapes bends below this straight line on account of 'negative' interactions. In this study, the interaction fields themselves have been measured by a process of re-linearization of the Henkel plot into the form of eq. (1) above. This has been done for a wide selection of commercial audio, video and digital tape media by replotting the Henkel plot data points in terms of an effective field which is the vector sum of the applied field and an interaction field which is taken as directly proportional to the tape magnetization.