The core symbol in below diagram indicates that it is an iron core material but Iam not sure whether it is correct. I see the same representation in many other circuit schematics as well.
Below ref says "To prevent saturation, the differential mode inductor must be made with a core that has a low effective permeability (gapped ferrites or powder cores). The common mode inductor, however, can use a high permeability material and obtain a very high inductance on a relatively small core"
"For the most part, ferrites are the material of choice for common mode inductors"
Were all the diagrams just a loose non- rigorous representation? Or was there any meaning in that core representation?