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Alnico is an acronym referring to a family of iron alloys which in addition to iron are composed primarily of aluminium (Al), nickel (Ni) and cobalt (Co), hence ''al-ni-co''. They also include copper, and sometimes titanium. Alnico alloys are ferromagnetic, with a high coercivity (resistance to loss of magnetism) and are used to make permanent magnets. Before the development of rare earth magnets in the 1970s, they were the strongest type of magnet. Other trade names for alloys in this family are: ''Alni, Alcomax, Hycomax, Columax'', and ''Ticonal''. The composition of alnico alloys is typically 8–12% Al, 15–26% Ni, 5–24% Co, up to 6% Cu, up to 1% Ti, and the balance is Fe. The development of alnico began in 1931, when T. Mishima in Japan discovered that an alloy of iron, nickel, and aluminum had a coercivity of 400 oersted (Oe; 32 kA/m), double that of the best magnet steels of the time. ==Properties== Alnico alloys make strong permanent magnets, and can be magnetised to produce strong magnetic fields. Of the more commonly available magnets, only rare-earth magnets such as neodymium and samarium-cobalt are stronger. Alnico magnets produce magnetic field strength at their poles as high as 1500 gauss (0.15 tesla), or about 3000 times the strength of Earth's magnetic field. Some brands 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's remanence (B''r'') may exceed 12,000 G (1.2 T), its coercivity (H''c'') can be up to 1000 oersted (80 kA/m), its energy product ((BH)max) can be up to 5.5 MG·Oe (44 T·A/m). This means alnico can produce a strong magnetic flux in closed magnetic circuit, but has relatively small resistance against demagnetization. Alnico alloys have some of the highest Curie temperatures of any magnetic material, around , although the maximum working temperature is normally limited to around .〔(Arnold-Alnico Magnets ). Arnoldmagnetics.com. Retrieved on 2011-07-30.〕 They are the only magnets that have useful magnetism even when heated red-hot. This property, as well as its brittleness 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. Alnico magnets are electrically conductive, unlike ceramic magnets. As of 2008, Alnico magnets cost about $44/kg ($20/pound) or $4.30/BHmax.〔(Frequently Asked Questions ). Magnetsales.com. Retrieved on 2011-07-30.〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Alnico」の詳細全文を読む スポンサード リンク
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