Magnetization:

Magnetic moment per unit volume, resulting from the individual magnetic moments contributed by atoms or molecules of the material; symbol M, units A/m (amps per metre); expresses how much a material is magnetized. For diamagnetic materials, magnetization opposes the external field; for paramagnetic materials, it reinforces it. In these cases, the magnetization is proportional to the eternal field. For ferromagnets this proportionality fails, and M can be large, even with no external field.