A permanent magnet is magnetized by application of a strong outer magnetic field. This magnetic field forces the spins of the atomic electrons stepwise into its own direction. With increasing outer field the magnet will trace the new curve. If the outer field strength is bigger than the saturation field strength all the spins have been oriented with the field. A high magnetization will not be possible from there on.

In case of permenent magnets this is an irreversible process. The magnet remains magnetized when the outer field goes back to zero. It will go back to the remanence point Br.

In case of weak magnets it may come to self demagnetiation due to its own feld. Normal iron would be demagnetized almost back to zero. Weaker permanent magnets such like AlNiCo or Cobold alloys might have to be stabilized by wel engineered geometries.