Editing Mu-metal (section)

==Application==
[[File:Mu metal CRT shields.jpg|thumb|Mu-metal shields for [[cathode-ray tube]]s (CRTs) used in [[oscilloscope]]s, from a 1945 electronics magazine]]
Mu-metal is a soft magnetic alloy with exceptionally high magnetic permeability. The high permeability of mu-metal provides a low [[reluctance]] path for [[magnetic flux]], leading to its use in [[Magnetic shielding|magnetic shields]] against static or slowly varying magnetic fields. Magnetic shielding made with high-permeability alloys like mu-metal works not by blocking magnetic fields but by providing a path for the [[magnetic field line]]s around the shielded area. Thus, the best shape for shields is a closed container surrounding the shielded space. 

The effectiveness of mu-metal shielding decreases with the alloy's permeability, which drops off at both low field strengths and, due to [[Magnetic saturation|saturation]], at high field strengths. Thus, mu-metal shields are often made of several enclosures one inside the other, each of which successively reduces the field inside it. Because mu-metal saturates at relatively low fields, sometimes the outer layer in such multilayer shields is made of ordinary steel. Its higher saturation value allows it to handle stronger magnetic fields, reducing them to a lower level that can be shielded effectively by the inner mu-metal layers.<ref>{{Cite web |date=2019-10-22 |title=MuMetal Shielding Performance - MuMETAL® High Permeability Magnetic Shielding Alloy ASTM A753 |url=https://web.archive.org/web/20191022014848/https://www.mu-metal.com/shielding-fundamentals.html |access-date=2025-04-07 |website=web.archive.org}}</ref><ref>{{Cite web |title=MuMETAL® Technical Data Sheet {{!}} Magnetic Shield Corporation |url=https://www.magnetic-shield.com/mumetal-technical-data/ |access-date=2025-04-07 |website=www.magnetic-shield.com}}</ref>

[[Radio frequency|RF]] magnetic fields above about 100 [[Kilohertz|kHz]] can be shielded by [[Faraday cage|Faraday shields]]: ordinary conductive metal sheets or screens which are used to shield against [[electric field]]s.<ref>{{cite web| title = Magnetic Fields and Shields| work = FAQ| publisher = Magnetic Shield Corp.| url = http://www.magnetic-shield.com/faq/interference.html| access-date = 2008-12-14| archive-date = 2008-12-18| archive-url = https://web.archive.org/web/20081218190613/http://magnetic-shield.com/faq/interference.html| url-status = dead}}</ref> [[Superconducting]] materials can also expel magnetic fields by the [[Meissner effect]], but require [[cryogenic]] temperatures.

The alloy has a low coercivity, near zero magnetostriction, and significant anisotropic magnetoresistance. The low magnetostriction is critical for industrial applications, where variable stresses in thin films would otherwise cause a ruinously large variation in magnetic properties.