Transverse susceptibility studies of recording media
A highly sensitive transverse susceptometer has been developed for the investigation of magnetic recording media. The susceptometer was based on the design of Pareti and Turilli with modifications to the solenoid and sensing coils. The modifications have resulted in an improvement in the signal to baseline ratio of a factor of 525, and a reduction in random noise. The increase in the sensitivity of the susceptometer allowed the investigation of Advanced Metal Particle (AMP) tapes and the measurement of the imaginary component of the transverse susceptibility (TS) proposed by Papusoi. Also, a modification was developed which allowed the investigation of the non-linear TS, proposed by Chantrell et al. The work reported for the latter two techniques was the first experimental demonstration of these measurements on magnetic recording media. Samples of Co-y-Fe203, Cr02, mixed y-Fe203 / Cr02 and AMP tapes were investigated, as were y- Fe201, Cr0 2 and AMP powders. The investigations suggested that the incoherent reversal mode was dominant in the systems containing Cr02, with coherent reversal dominant in the remaining systems. The anisotropy peaks measured using the non-linear IS were found to be less dependent on sample texture than those of the traditional linear measurement. In particular the anisotropy peaks of the non-linear TS for incoherently reversing systems appeared to be independent of texture and it was proposed that these were a direct measure of the anisotropy field distribution, although independent verification was not performed. The determination of magnetic coating thickness after Sollis and Bissell was extended to allow the measurement of AMP tapes. A computer model was developed to investigate the error in the technique due to the particulate nature of the coating. The results of the model indicated that the error increased as coating thickness and volume packing fraction decreased. Correction factors were determined for MP3 and MP4 particle based systems. The detection of the imaginary component of TS and its close agreement with the theoretical predictions of Papusoi suggested that the dassification of TS as a 'stiffness' method of anisotropy field determination might be in error.