The magnetic field device includes a first magnet, a first ferromagnetic element disposed adjacent to the first magnet, a second magnet, and a gap between the first ferromagnetic element and the second ferromagnetic element. A second ferromagnetic element disposed relative to the first ferromagnetic element adjacent to the second magnet to produce a gap between the first ferromagnetic element and the second ferromagnetic element Having a third magnet disposed therein. [Selection] Figure 1B磁場デバイスは、第１の磁石、第１の磁石に隣接して配置された第１の強磁性素子、第２の磁石、第１の強磁性素子と第２の強磁性素子との間にギャップを生み出すために第２の磁石に隣接して第１の強磁性素子に対して配置された第２の強磁性素子、および第１の強磁性素子と第２の強磁性素子との間でギャップ内に配置された第３の磁石をもつ。【選択図】図１Ｂ
