Magnetization Processes in a Polycrystalline Manganese Zinc Ferrite

Magnetic domains

“…At greater values of 0 (4"-7") ' lozenges ' are formed ; rows of discrete structures elongated in the [loo] direction and arranged in rows perpendicular thereto. These are similar to certain patterns found on single crystals (Bates and Hart 1953) and have been interpreted as representing the intersection with the surface of rows of transverse spikes, originating at inclusions during demagnetization (Bates and Davis 1956). As they resemble the isolated elliptical figures found on some slightly mis-oriented surfaces of uniaxial crystals, it seems possible that they might represent the intersection of reverse spikes originating at internal grain boundaries.…”

“…When the patterns on accurately aligned axial planes of cobalt crystals are studied, the walls remain straight and parallel during their movement, but their spacing is not that of the internal domains, since they meet and disappear when the crystals are magnetized to about only one-third of saturation. Although the reason is not apparent, the behaviour of walls on axial planes of magnetoplumbite specimens (Bates, Craik, Griffiths and Isaac 1960) corresponds more to the expected behaviour of internal domains. Here it is seen that the equally-spaced parallel lines which correspond to the demagnetized state become curved when a field is applied, so that they approach in the central regions but maintain the same spacing at the ends (Fig.…”

“…12(f) shows some four concentric reverse spikes while the principal 180" walls are greatly distorted. The axial planes of large crystals are readily examined ; the patterns represent 180" walls intersecting the surface to give straight parallel lines which on magnetization move together in pairs as described below (Bates, Craik, Griffiths and Isaac 1960).…”

“…When a single crystal boule of manganese ferrite, grown by the flame fusion method, is cleaved as a preliminary to surface orientation, two distinct types of pattern are found (Bates, Craik and Griffiths 1958). The surface approximates to a (100) plane, and the large-scale patterns shown in Fig.…”

“…It is easy to observe characteristic domain structures in large-grain barium ferrites after careful mechanical polishing (3 4.3), although this treatment obscures the structures on very fine grains ; because of the low anisotropy of the cubic ferrites such polishing tends to give strain patterns which are not characteristic of the internal structure (Bates, Clow, Craik and Griffiths 1958). T h e strain patterns can be removed by etching, but this is not satisfactory, since grain boundaries are selectively etched away and the generally porous material is attacked internally, leaving surfaces pitted.…”