One of the best shielding materials for low frequency magnetic field applications is nickel-iron with a nickel content of around 80%, widely known als "Mumetal, Mumetall, µ-Metal". Unfortunately, where a "µ" is around, there ist not necessarily 80% nickel, "Mu-metal" inside .......
Systron uses 80% nickel-iron, "mu-metal" primarily in it's LabShield® shielding systems for room shielding applications where best magnetic DC- and AC-field attenuation is needed. Mu-metal is perfectly suitable for applications where no strong magnets, such as NMR's are around, as mu-metal would saturate in these strong fields. However, static earth magnetic field and slow varying DC shifts are perfectly attenuated, as well as AC fields with mains frequencies, as long as the mu-metal has received the right heat treatment and has been properly handled. The presence of stronger fields might require the use of alternative alloys such as pure iron or silicon iron.
According to Wikipedia, Mu-metal is defined as follows:
Mu-metal is a nickel–iron soft ferromagnetic alloy with very high permeability, which is used for shielding sensitive electronic equipment against static or low-frequency magnetic fields. It has several compositions. One such composition is approximately 77% nickel, 16% iron, 5% copper, and 2% chromium or molybdenum.
More recently, mu-metal is considered to be ASTM A753 Alloy 4 and is composed of approximately 80% nickel, 5% molybdenum, small amounts of various other elements such as silicon, and the remaining 12 to 15% iron. The name came from the Greek letter mu (μ) which represents permeability in physics and engineering formulae. A number of different proprietary formulations of the alloy are sold under trade names such as MuMETAL, Mumetall, and Mumetal2....... continue reading in Wikipedia