Nickel is a higher permeability lower loss magnetic material when compared to silicon steel. It is usually used in combination with iron. Saturation for a fifty-fifty percent combination is around 15 kilogauss. Saturation for an 80% nickel combination is around 8 kilogauss. For the same power rating, a transformer made with Nickel iron will be larger than a silicon steel transformer provided they are operated in the silicon steels useful frequency range. At higher frequencies Nickel iron is preferred over silicon steel. Nickel iron is more expensive than silicon steel. Nickel iron, because of its higher permeability and lower losses it preferred over silicon steel for high fidelity applications even at the lower frequencies suitable for silicon steel. Nickel iron can be operated beyond 10 kilohertz with proper choice of strip thickness and kilogauss level. Ferrites can match the lower losses of Nickel iron but cannot match the saturation level or the high permeability.
Nickel iron can be processed to optimize either round loop or square loop properties.