Domain wall interactions with non-magnetic inclusions observed by Lorentz microscopy

Abstract

A theory of spike formation around non-magnetic inclusions or voids is presented for biaxial type films in the manner reviewed by Craik and Tebble in 1965. The dependence of spike length on hole size and film thickness is determined. From the theory and observations, using Lorentz microscopy on single-crystal iron specimens, it is shown that a minimum hole size exists below which it is energetically unfavourable for spikes to nucleate. Around some holes below the minimum size a `web' type domain structure occurs and increases the effective hole size allowing spikes to nucleate on their extremities.From the results it appears that an increase in 90° wall energy γbar, above 90 from 1·0 ergs cm−2 at 400 Å thickness to 1·3 ergs cm−2 at 1557 Å gives good agreement with theory. This implies that certainly up to this thickness and probably for some considerable increase in thickness, the walls are of the Néel type and not the Bloch type as previously thought.