Transverse susceptibility measurements on particulate recording media

Abstract

An experimental investigation of transverse susceptibility (Xi) measurements on particulate recording media has been made. The main use of this measurement is to determine the anisotropy field (Ilk) of a material which is one of its intrinsic properties. Previous theoretical modelling of Xi was reviewed and a description given of the apparatus constructed to carry out the measurements.
Xi was measured on a variety of experimental and commercial samples. The experimental systems investigated comprised of samples prepared from Cr02 , Co -Fe2 03 and Ba-ferrite. Results from the textured systems showed good agreement
with theory, with the curves displaying peaks at 14 and hysteresis in the low field region. An investigation into the suppression of the 14 peaks in random powder samples was shown to result from texture rather than particle interactions as had previously been suggested. Hysteresis in the X. response was examined using difference curves which were made by subtracting field sweeps from opposing directions.
The variations found between experiment and theory were accounted for in terms of texture and the reversal mechanism.
Using Xe measurements a method was developed enabling bulk magnetisation values for tape samples to be determined. When combined with VSM measurements these values were used to give a measure of the magnetic layer thickness.
Comparative thickness values were also measured using a surface roughness technique. Xi and standard magnetic measurements were used to investigate the dispersion process which is currently of considerable interest. This was carried out by preparing samples of wet dispersion and dry hand spreads from various production stages. A study on a Cr02 system was made as part of a programme of measurements between a number of European laboratories. Results from Xi and remanence measurements were shown to be sensitive to subtle changes in dispersion quality due to processes such as solvent letdown. Measurements on a Ba-ferrite pigment were used to study the process of platelet stacking which was shown to result primarily from orientation.
In addition the Xe measurements were found to be more sensitive to changes in the dispersion properties than remanence measurements.