A magnetic field generating device is disclosed having an arrangement of permanent magnets, each permanent magnet (PM) having a north end and a south end, and each aligned in the same north-south orientation. The PM arrangement is configured to have a surface at the north polarity end, a surface at the south polarity end, or a surface at both ends. A layer of ferromagnetic material is securely disposed at one of the surfaces of the PM arrangement, the layer having a thickness equal to or less than about 15 millimeters.