Magnets can be re-magnetized when the magnet is demagnetized by several factors. When magnetizing pickups, a few methods can be used. One method is using a semi-continuous DC magnetizer that uses iron core electromagnets that are energized by filtered direct current. They have adjustable and interchangeable pole pieces to fit most rod and bar magnets used in musical instrument pickups. I’ve used powerful horseshoe magnets to magnetize bar and rod magnets. Some manufacturers magnetize the rod or bar magnet one at a time before the bobbin or flatwork is fabricated and others magnetize the magnet(s) after the pickup is completely assembled.

There are also capacitor-discharge magnetizers, half cycle, DC-bias/AC-inrush type and other special purpose types.