Magnetic recording forms the basis of one of the largest international industries. Electron microscopy has of course played a significant role in relating magnetic performance to the underlying microstructure. However, relatively little attention has been paid to the ways in which imaging of the magnetic structure can be correlated with processing conditions and microstructural parameters. The present research has been aimed to address this deficiency.

A method was devised to prepare samples with large electron transparent areas (e.g., 250 microns square) from real computer hard discs. Fresnel TEM images were taken in a Philips CM20 FEG equipped with a special Lorentz pole piece, and with the objective lens off. Upon defocusing, the ferromagnetic domain structure strikingly appears. The characteristics of the recorded tracks depend on the magnetic state of the disc prior to magnetic “writing”, and much information about the local direction of magnetization could be obtained from the nature of the magnetic “ripple” structure.