Domain Structures and Coercivity of Alcomax III

Abstract

Bitter figure and electron-micrograph studies have been made of (i) field-cooled, (ii) optimum and (iii) over-aged specimens of Alcomax III cut from the same test block and subjected to the appropriate thermal treatments. The photographic records taken during the description of a hysteresis loop with each specimen have been compared. The general domain structure of all three specimens consists of 180° domains and spikes of reverse magnetization, and is superficially typical of a uniaxial material like cobalt. Significant differences between the structures of the three specimens are discussed; in particular, in the optimum specimen there are no marked changes in domain directions across grain boundaries, the domain walls are less clear than in the other specimens, and the domains are narrower. On planes perpendicular to the field applied during cooling, normal Lifshitz closure domains are formed in case (i), complex free pole structures in case (ii) and coarser free pole structures in case (iii). An interpretation of the observed phenomena is suggested in terms of magnetic interaction domains.