General Introduction
1, Alnico alloys make strong permanent magnets, and can be magnetized to produce strong magnetic fields.
2, Of the more commonly available magnets, only rare-earth magnets such as neodymium and samarium-cobalt are stronger.
3, 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.
4, Some brands of alnico are isotropic and can be efficiently magnetized in any direction.
5, Other types, such as alnico 5 and alnico 8, are anisotropic, with each having a preferred direction of magnetization, or orientation.
6, Anisotropic alloys generally have greater magnetic capacity in a preferred orientation than isotropic types.
7, Alnico's remanence (Br) may exceed 12,000 G (1.2 T), its coercivity (Hc) 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).
8, This means alnico can produce a strong magnetic flux in closed magnetic circuit, but has relatively small resistance against demagnetization.
9, Anisotropic alnico magnets are oriented by heating above a critical temperature, and cooling in the presence of a magnetic field.
10, Both isotropic and anisotropic alnico require proper heat treatment to develop optimum magnetic properties — without it alnico's coercivity is about 10 Oe, comparable to technical iron, which is a soft magnetic material. After the heat treatment alnico becomes a composite material, named "precipitation material"—it consists of iron and cobalt rich precipitates in rich-NiAl matrix.
11, Alnico's anisotropy is oriented along the desired magnetic axis by applying an external magnetic field to it during the precipitate particle nucleation, which occurs when cooling from 900 °C (1,650 °F) to 800 °C (1,470 °F), near the Curie point.
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