US Patent 7821366 Magnetic circuit and method of applying magnetic field

In a magnetic circuit for providing magnetic anisotropy in the in-plane radial direction of a soft magnetic under layer, magnets for perpendicular magnetization are respectively provide on the north and south poles of a magnet for horizontal magnetization. When magnetic circuits configured thus are stacked in a plurality of stages, a magnetic field (air-gap magnetic field) formed in a gap between the magnetic circuits is superimposed by magnetic fields from the magnets for perpendicular magnetization as well as a magnetic field from the magnet for horizontal magnetization (in-plane magnetization). The pole faces of the magnets for perpendicular magnetization are disposed closer to the gap between the magnetic circuits, so that a stronger magnetic field can be formed in the gap.