Saturation (magnetic)

(Though, magnetization continues to increase very slowly with the field due to paramagnetism.)

Saturation is a characteristic of ferromagnetic and ferrimagnetic materials, such as iron, nickel, cobalt and their alloys.

[9] Saturation puts a practical limit on the maximum magnetic fields achievable in ferromagnetic-core electromagnets and transformers of around 2 T, which puts a limit on the minimum size of their cores.

In applications in which the weight of magnetic cores must be kept to a minimum, such as transformers and electric motors in aircraft, a high saturation alloy such as Permendur is often used.

This means that their inductance and other properties vary with changes in drive current.

In linear circuits this is usually considered an unwanted departure from ideal behavior.

When AC signals are applied, this nonlinearity can cause the generation of harmonics and intermodulation distortion.

To prevent this, the level of signals applied to iron core inductors must be limited so they don't saturate.

To lower its effects, an air gap is created in some kinds of transformer cores.

These are used in variable fluorescent light ballasts, and power control systems.