Mu-metal

Mu-metal is a nickel-iron alloy (approximately 75% nickel, 15% iron, plus copper and molybdenum) that has very high magnetic permeability. The high permeability makes mu-metal very effective at screening static or low-frequency magnetic fields, which cannot be attenuated by other methods. The name came from the Greek letter mu (μ) which represents permeability. A number of different proprietary formulations of the alloy are sold under trade names such as Mumetal, MuMetal, and MuShield; this article will cover their common features.