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Old hard drive brackets, made of Mu-metal.

Mu-metal, also known as Mu metal or Mumetal is a nickeliron soft magnetic alloy with very high permeability widely used for shielding sensitive electronic equipment against magnetic fields. The name of the alloy comes from the Greek letter mu (μ), which the symbol for magnetic permeability.

The alloy is sold under various trade names, such as MuMETAL, Mumetall, and Mumetal2.


The alloy has several compositions, the most common being 77% nickel, 16% iron, 5% copper and 2% chromium or molybdenum. Other types include ASTM A753 Alloy 4 which consists of 80% nickel, 12 to 15% iron, 5% molybdenum and other elements such as silicon.


Mu-metal is resistant to corrosion, though acids will slowly dissolve it in the presence of oxygen.


Mu-metal is commonly encountered in the form of HDD magnet brackets. Old hard drives tend to have big brackets.

Other sources of Mumetal are old submarine cables and cathode ray tube brackets.


  • Extract elemental nickel
  • Magnetic shielding



Mu-metal is relative inert, but due to it's high nickel percentage, it may cause dermatitis to some people.


In closed containers.


Best to try to recycle it.


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