Mu-metal
19196
223085026
2008-07-02T14:27:30Z
139.91.197.112
/* Uses and properties */
'''Mu-metal''' is a [[nickel]]-[[iron]] [[alloy]] (75% [[nickel]], 15% [[iron]], plus [[copper]] and [[molybdenum]]) that has very high [[Permeability (electromagnetism)|magnetic permeability]]. Permeability is represented by [[Mu (letter)|μ]].
The high permeability makes mu-metal very effective at screening static or low-frequency [[magnetic field]]s, which cannot be attenuated by other methods.<ref name="http://www.analog.com/UploadedFiles/Application_Notes/41727248AN_347.pdf">[http://www.analog.com/UploadedFiles/Application_Notes/41727248AN_347.pdf http://www.analog.com/UploadedFiles/Application_Notes/41727248AN_347.pdf]</ref>
Mu metal requires special [[heat treatment]] — [[Annealing (metallurgy)|annealing]] in [[hydrogen]] atmosphere, which reportedly increases the [[magnetic permeability]] about 40 times. The annealing alters the material's [[crystal structure]], aligning the grains and removing some impurities, especially [[carbon]]. Mechanical treatment may disrupt the material's grain alignment, leading to a drop in the permeability of the affected areas, which can be restored by repeating the hydrogen annealing step.
==Uses and properties==
Mu-metal is used to shield equipment from magnetic fields. For example:
* [[Vacuum chamber]]s for experiments with low-energy [[electron]]s, for example photoelectron spectroscopy
* [[Magnetic resonance imaging]] equipment
* The [[magnetometer]]s used in [[magnetoencephalography]] and [[magnetocardiography]]
* [[Photomultiplier]]s
* [[Cathode-ray tube]]s used in analog [[oscilloscopes]]
* [[Superconducting]] circuits and esp. [[Josephson junction]] circuits
* [[Electric power]] [[transformer]]s, which are built with mu-metal shells to prevent them from affecting nearby circuitry
* [[Magnetic cartridge]]s, which have a mu-metal case to reduce interference when [[Gramophone record|LP]]s are played back
* [[Hard Disk|Hard Drives]], which have mu-metal backings to the magnets found in the drive
Other materials with similar magnetic properties are [[supermalloy]], supermumetal, [[nilomag]], [[sanbold]], Molybdenum [[Permalloy]],[[Sendust]] ,[[Ultraperm]], [[M-1040]], [[Hipernom]], [[HyMu-80]], etc.
==References==
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==External links==
* [http://arxiv.org/abs/cond-mat/0306016 Giant Magnetoimpedance in Crystalline Mumetal]
[[Category:Nickel alloys]]
[[Category:Magnetic alloys]]
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