I'm not sure if it would change the wave field of the magnet or not but 303 and 304 type stainless is Austenitic so they may work for you. Linked some info below.
https://www.kjmagnetics.com/blog.asp?p=shielding-materials
https://www.kjmagnetics.com/blog.asp?p=stainless
https://www.kjmagnetics.com/blog.asp?p=shielding-materials
https://www.kjmagnetics.com/blog.asp?p=stainless