On the Toroidal Arrangement of the 180° Domain Walls in Ring Polycrystalline Soft Ferrites

Abstract
According to an assumption proposed by Globus in 1976, special ring-shaped polycrystalline soft ferrites could have a toroidal arrangement of their magnetic domains (so-called "magnetic ring" concept). Experiments in the past have shown that this property must be restricted to the defect-free grain microstructures. This paper gives two examples of investigations wich confirm the good validity of the concept. The first example is concerned with the magnetoelastic effects of the mechanical compression applied along the circumferences of the ring sample. λ being negative (YIG), the spins are forced to align in the stress direction leading to a more or less marked increase of the initial susceptibility (measurement is made in the same direction as the stress applied) according to the aptitude of the sample investigated to obey the above concept. In the most favourable cases, the axial direction (the revolution axis of the ring), can be then approached as a true "hard magnetization" axis, so that it becomes possible to interpret the magnetization in this direction as an irreversible rotational process. The second investigation is thus the analysis of the magnetization in this so-called "hard" direction. Comparisons with a theoretical development of the hysteresis of rotation are made which lead to good agreements.