Mu-metal

Other ratios are also common, such as 80% Ni, 16 % Fe and 4% Co.

Permalloy / Supermalloy: 78.5 % Ni; 3 % Mo

Mu - metal ( μ - metal, mu-metal, English Mu -metal or permalloy English ) is a soft magnetic nickel -iron alloy ( approximately 70-81 % nickel, and possibly also traces of molybdenum, cobalt, chromium or manganese) high magnetic permeability, which is used for shielding low frequency magnetic fields, and for the preparation of the ferromagnetic cores of signal transformers, magnetic flux sensors and current transformers.

Properties

Mu - metal has a high permeability ( = 50000-140000 ), which causes the magnetic flux of low frequency magnetic fields are concentrated in the material. This effect results in shielding of low frequency or static magnetic interference fields caused a significant attenuation of shielding.

If Mu - metal bent, deformed or mechanically processed, breaking the high permeability drastically. Values ​​up to = 150 are possible down. Therefore, Mu - metal should definitely be re-annealed after mechanical stress to recover by annealing of lattice defects the high permeability.

Mu - metal, there are in the form of films and sheets of a thickness ranging from about 0.1 to 5.0 mm in standard dimensions, and in addition to a plate shape.

Areas of application

• As a magnetoresistive element in hard disk heads. The resistance of the element can be influenced by changing the surrounding magnetic field. (see magnetoresistive effect)
• The core material for low-frequency transformers, current transformers, magnetic current sensors
• In powder form for the preparation of compressed powder cores
• In the form of thin sheets as material for shielding magnetic interference in electronic devices or watch cases. It finished shields with typical wall thicknesses of 1 to 2 mm in standard shapes such as cups, pipes and hoses are available. Furthermore, there are Abschirmhauben for magnetic heads, monitor picture tubes, cups for automotive gauges and screens for small electric motors in tape recorders
• Shielded enclosures: Walkin shielded enclosures or rooms with multi-shell shields have been built for magnetic field -free studies or high-field laboratories.

Production

The molten alloy is processed after cooling into sheets in strip form or wire. Mu - metal can punch up, etching, deep drawing, bending, soldering, welding and galvanic coating. As cutting shapes, drilling and grinding are possible. The finished workpiece is exposed after machining a final annealing at 1000 to 1200 ° C and a subsequent annealing treatment at 400-600 ° C. These thermal treatments are performed under vacuum or inert gas such as hydrogen. By special cooling process or Magnetfeldglühungen particularly high permeabilities or other special magnetic properties can be achieved.