Someone (and i apologize for forgetting your name as well as deleting your original message) had sent me a message regarding what material was best for magnetic shielding for a 200kHz DRSSTC. Anyways, the best material for magnetic field shielding would be copper, however remember, that with shielding, actual attenuation is actually more dependent on the physical structure of the shield (slots, holes, etc...) rather than the property of the material itself.