ON THE TOROIDAL ARRANGEMENT OF THE 180-DEGREES DOMAIN-WALLS IN RING POLYCRYSTALLINE SOFT FERRITES

According to an assumption proposed by Globus in 1976, special ring-sh aped polycrystalline soft ferrites could have a toroidal arrangement o f their magnetic domains (so-called ''magnetic ring'' concept). Experi ments in the past have shown that this property must be restricted to the defect-free grain microstructures. This paper gives two examples o f investigations which confirm the good validity of the concept. The f irst example is concerned with the magnetoelastic effects of the mecha nical compression applied along the circumferences of the ring sample. lambda being negative (YIG), the spins are forced to align in the str ess direction leading to a more or less marked increase of the initial susceptibility (measurement is made in the same direction as the stre ss applied) according to the aptitude of the sample investigated to ob ey the above concept. In the most Favourable cases, the axial directio n (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 proc ess, The second investigation is thus the analysis of the magnetizatio n in this so-called ''hard'' direction. Comparisons with a theoretical development of the hysteresis of rotation are made which lead to good agreements.