|How does a magnet manufacturer make a permanent magnet—how does it vary in strength?
The manufacturer assembles the magnet from hard magnetic materials. These materials are intrinsically magnetic (ferromagnetic) so that they have tiny magnetic domains inside. They are hard, meaning that these domains have great difficulty changing their magnetic orientations. As the final processing step, the finished magnets are exposed to an extremely strong magnetic field; so strong that it flips all of the domains into the desired direction. The domains become trapped in this new orientation and the magnet becomes permanently magnetized. Unless it is exposed to other very strong fields or excessive heat or shock, it will remain permanently magnetized indefinitely.