How do you suppress a magnetic feild?

Question

What material works best to sheild one feild from another, and how thin can it be?

Answer 1

Certain metal alloys, called mu metals, will block magnetic fields. These are often used in small loudspeakers that are used near cathode ray tubes (CRTs). Since CRTs are affected by magnetism and since loudspeakers have strong magnets, mu metal shields the CRT from the speaker's magnet.

Dunno about thickness but the shields I've seen are on the order of 16-gauge (perhaps 1 mm).