Abstract: A permanent magnet magnetic circuit comprises a main magnet block having a pair of opposite outer surfaces. A pair of main magnetic poles of opposite polarities are disposed on the respective outer surfaces of the main magnet block. The main magnet block is provided with a channel defined between the pair of outer surfaces and the channel has a pair of inner surfaces corresponding to the respective outer surfaces of the main magnet block. The main magnet block is also provided with a pair of oppositely polarized compensating magnetic poles arranged on the respective inner surfaces for controlling any vector of the magnetic field directed from one of the main magnetic pole to the other main magnetic pole. A pair of adjusting magnet blocks are arranged on the respective inner surfaces to adjust the magnetic field directed from one of the main magnetic poles to the other magnetic pole.

Abstract: A permanent magnet magnetic circuit is provided capable of producing a unidirectional magnetic field substantially free of unnecessary perpendicular magnetic field components. A pair of main magnetic poles of opposite polarities are situated at a pair of opposite edge surfaces of a permanent magnet block for producing lines of magnetic force. One major surface of the block between the edge surfaces is provided with a channel where a pair of auxiliary magnetic poles are situated at opposed inner surface portions of the channel for controlling a middle portion of the lines of magnetic force to be linear.

Abstract: A rubber or plastic magnet of high magnetic properties is produced by incorporating a magnetoplumbite type magnetic powder into a rubber or thermoplastic or thermosetting matrix at a high concentration with a high degree of orientation of the magnetic particles. Such high concentration and orientation can be obtained by using a magnetoplumbite type magnetic powder having a compressed density in the range between 3.30 g/cm.sup.3 and about 3.55 g/cm.sup.3 and an average particle size of about 1.00 and 1.50.mu., said particles being prepared by dry crushing process from coarse sintered particles and having predominantly single crystal structure.