Could be some sort of alloy of nickle-steel, but usually we dont try to figure out what kind of material we have based solely on the permeability unless the choices are narrowed down a lot. Usually the manufacturer tells *us* what their material can do and we make a note of it. Two manufacturers could make different alloys with similar characteristics so we wouldnt really know what we had unless we are given a short list to pick from.
Maybe you are just trying to characterize the material, but it's better to ask the manufacturer (look on their data sheets).