Irreversible loss

If we increase the temperature to the Curie temperature, a magnet will permanently lose its magnetism. The atoms vibrate so intensely that there is no longer any global orientation. The material demagnetizes. Mechanical shocks, oxidation or exposure to very strong external fields can also make the magnetism disappear permanently.

This loss cannot be repaired = irreversible.

On the other hand, we have reversible loss: temporary loss of magnetism, e.g. due to a change of temperature. This loss can be reversed by cooling or remagnetization.