Properties and Applications of Ferromagnetic Materials

Ferromagnetic materials having low retentivities are widely used in power and communication
apparatus. Since silicon iron has high permeability and saturation flux density,
It is extensively used in the magnetic circuits of electrical machines and heavy current apparatus where a high flux density
is desirable in order to limit the cross-sectional area and, therefore, the weight and cost.
Thin siliconiron laminations (clamped together but insulated from each other by varnish, paper or their own
surface scale) are used in the construction of transformer and armature cores where it is essential to
minimize hysteresis and eddy-current losses.
In field systems (where flux remains constant), a little residual magnetism is desirable. For such
systems, high permeability and high saturation flux density are the only important requirements which
are adequately met by fabricated rolled steel or cast or forged steel.
Frequencies used in line communication extend up to 10 MHz whereas those used in radio vary
from about 100 kHz to 10 GHz. Hence, such material which have high permeability and low losses
are very desirable.
For these applications, nickel-iron alloys containing up to 80 per cent of nickel
and a small percentage of molybdenum or copper, cold rolled and annealed are very suitable.