Abstract: A rotary transformer includes a rotor core formed by stacking channel parts to form a required number of channels. Each channel part is formed by stacking two kinds of annular magnetic rings so that two rings having the same outside and inside diameters are placed at both sides of a ring having the same inside diameter as the two rings but a greater outside diameter than the two rings. A stator core is also formed by stacking channel parts to form the required number of channels. The channel part is formed by stacking two kinds of annular magnetic rings so that two rings having the same outside and inside diameters are placed on both sides of a ring having the same inside diameter with the two rings but smaller outside diameter than the two rings. A thin layer of glass can be used to bond the rings of the stator or rotor together.

Abstract: An Mn-Zn-based single crystal ferrite composition containing an additive material essentially consisting of 0.2 to 2 mole % SnO.sub.2, 0.1 to 1 mole % CoO, 0.2 to 1 mole % CaCO.sub.3 and 0.02 to 1 weight % V.sub.2 O.sub.5 added to a host material essentially consisting of 51 to 54 mole % Fe.sub.2 O.sub.3, 27 to 33 mole % MnO and 16 to 20 mole % ZnO. A magnetic head manufactured from the single crystal ferrite generates an enhanced reproduction output and a reduced rubbing noise, thereby achieving a high picture quality and a high resolution of images.