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== <div class="references-small"> <references/> </div> ==External links== * [http://arxiv.org/abs/cond-mat/0306016 Giant Magnetoimpedance in Crystalline Mumetal] [[Category:Nickel alloys]] [[Category:Magnetic alloys]] [[de:Mu-Metall]] [[fr:Mu-métal]] [[it:Mu-metal]] [[nl:Mumetaal]] [[pl:Mumetal]]