Magnetic saturation is the state reached in a sample when increases in applied external magnetic field H cannot increase the magnetization of the material further. At saturation, the total magnetic flux density B does not increase with increases in applied external fields. Saturation is a characteristic of ferromagnetic and ferrimagnetic materials, such as iron, nickel, cobalt and their alloys.
Saturation is most clearly seen in the Hysteresis loop (above).. As the H field increases, the B field approaches a maximum value asymptotically, denoted as the saturation magnetization of the substance.
Different materials have different saturation levels. High permeability iron alloys used in transformers reach magnetic saturation at 1.6–2.2 teslas (T), whereas ferrites saturate at 0.2–0.5 T. Some amorphous alloys saturate at 1.2–1.3 T. Mu-metal saturates at around 0.8 T.
source: Wikipedia