Alnico
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'''Alnico''' is an acronym<ref name="Hellweg">{{cite book
| title = The Insomniac's Dictionary
| edition =
| last = Hellweg
| first = Paul
| coauthors =
| year = 1986
| publisher = Facts On File Publications
| id = 0-8160-1364-0
| pages = 115}}</ref> referring to alloys which are composed primarily of [[aluminium]] (symbol '''Al'''), [[nickel]] (symbol '''Ni''') and [[cobalt]] (symbol '''Co'''), hence ''al-ni-co'', with the addition of [[iron]], [[copper]], and sometimes [[titanium]], typically 8-12% Al, 15-26% Ni, 5-24% Co, up to 6% Cu, up to 1% Ti, rest is Fe. The primary use of alnico alloys is magnet applications.
==Properties==
Alnico alloys make strong [[permanent magnet]]s, and can be magnetized to produce strong [[magnetic field]]s. Of the more commonly available magnets, only [[rare-earth magnet]]s such as [[neodymium magnet|neodymium]] and [[samarium-Cobalt magnet|samarium-cobalt]] are stronger. Alnico magnets produce magnetic field strength at their poles as high as 1500 [[gauss (unit)|gauss]] (0.15 [[tesla (unit)|tesla]]), or about 3000 times the strength of Earth's magnetic field. Some types of Alnico are [[isotropic]] and can be efficiently magnetized in any direction. Other types, such as Alnico 5 and Alnico 8, are anisotropic, with each having a preferred direction of magnetization, or orientation. Anisotropic alloys generally have greater magnetic capacity in a preferred orientation than isotropic types. Alnico remanence (B<sub>r</sub>) may exceed 12000 gauss (1.2T), its coercion force (H<sub>c</sub>) can be up to 1000 oersted (80kA/m), its energy product ((B*H)<sub>max</sub>) can be up to 5.5M Gs*Oe (44 T*A/m) - this means Alnico can produce high magnetic flux in closed magnetic circuit, but has relatively small resistance against demagnetization.
Alnico is produced by [[casting]] or [[sintering]] processes. Anisotropic alnico magnets are oriented by heating above a critical temperature, and cooling in the presence of a magnetic field. Both isotropic and anisotropic Alnico require proper heat treatment to get its magnetic properties - without it its coercion is about 10 Oe - comparable to technical iron, which is a soft magnetic material. After the heat treatment alnico becomes kind of composite material, named "precipitation material" - it consist of rich-Co precipitate in rich-NiAl matrix. Alnico anisotropy is oriented if it is in external magnetic field during the precipitate particle nucleation, which occur when cooling from 900 to 800 C, near Curie point. Without external field there are local anisotropies of different orientations, due to spontaneous magnetization. The precipitate structure is a "barrier" against magnetization changes, as it prefers few magnetization states requiring high energy to get the material into any intermediate state. Also, small magnetic field change magnetization of matrix phase only, and it is reversible.
Alnico alloys have some of the highest [[Curie point]]s of any magnetic [[Chemical substance|material]], around 800 °[[celsius|C]], although the maximum working temperature is normally limited to around 538 °C.<ref>[http://www.arnoldmagnetics.com/products/alnico/index.htm Arnold - Alnico Magnets<!-- Bot generated title -->]</ref> This property, as well as its [[brittle]]ness and high melting point, is the result of the strong tendency toward order due to [[intermetallic]] bonding between aluminium and its other constituents. They are also one of the most stable magnets if they are handled properly.
As of 2008, Alnico magnets cost about $20 per lb, $4.30 per BHmax.<ref>[http://www.magnetsales.com/Design/FAQs_frames/FAQs_frame.html Frequently Asked Questions<!-- Bot generated title -->]</ref>
==Use==
Alnico magnets are used in [[electric motor]]s, electric [[guitar pickup]]s, [[microphones]], [[sensor]]s, [[loudspeaker]]s, and [[cow magnet]]s.
==References==
<references/>
# Physical Review: [http://prola.aps.org/abstract/PR/v77/i6/p839_2 77p839_2], [http://prola.aps.org/abstract/PR/v80/i1/p112_2 80p112_2], [http://prola.aps.org/abstract/PR/v80/i2/p302_1 80p302_1], [http://prola.aps.org/abstract/PR/v81/i3/p478_1 81p478_1];
# Review of Modern Physics [http://prola.aps.org/abstract/RMP/v17/i1/p15_1 17p15], [http://prola.aps.org/abstract/RMP/v25/i1/p316_1 25p316_1];
# Journal of Applied Physics [http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JAPIAU000029000003000299000001&idtype=cvips&gifs=Yes 29p299], [http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JAPIAU000031000005000S82000001&idtype=cvips&gifs=yes 31pS82], [http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JAPIAU000040000003001308000001&idtype=cvips&gifs=Yes 40p1308].
[[Category:Aluminium alloys]]
[[Category:Nickel alloys]]
[[Category:Cobalt alloys]]
[[Category:Magnetic alloys]]
[[Category:Types of magnets]]
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