Eddy current loss
Eddy current loss is caused by small currents circulating
within the core material, stimulated by the alternating flux in the core.
The I2R power loss associated with these
currents produces heating of the core known as eddy current loss.
In iron-cored transformers, insulated iron sheets known
as laminations are used to minimize this effect by restricting the path
for circulating currents.
Ferrite cores restrict these paths even further.