Alnico Magnets

Alnico Magnets

As one of the members of magnets family, Alnico remains the workhorse of the permanent magnet industry and can be relied upon to deliver impressive flux density at an economical price. Alnico also boasts the lowest temperature coefficient of any commercial magnet material (0.02% per degree centigrade) allowing for excellent stability over a wide temperature range.

The most efficient use of Alnico requires that it be magnetized after the magnet has been assembled with its pole pieces into the final magnetic circuit. Magnetic saturation at the end-use location requires the application of a magnetizing force 4 to 5 times greater than the coercive force of the material. For Alnico 5, a magnetizing force of 3000 oersteds (240 KA/m) is recommended. For Alnico 8, the magnetizing force should be at least 7000 oersteds (560 KA/m). The magnetizing force need be applied only momentarily. Thus, impulse magnetizers employing a capacitor discharge are commonly used. Direct current magnetizers are also effective.

Stability & Temperature Effects

lnico magnets offer excellent stability with respect to temperature changes: reversible change is 0.02% per degree Centigrade. Heating may produce an irreversible loss of magnet strength. The magnitude of loss depends upon the dimensions of the magnet and its composition, but is usually less than 5%, and may be recovered by re-magnetization. At temperatures exceeding 1000oF (538ºC), a metallurgical change takes place which causes magnetic strength to reduce rapidly. This change will not be recovered by re-magnetization.

External magnetic fields can also induce partial demagnetization. In some critical applications, it is desirable to stabilize the magnet by intentionally reducing magnetic output by 5% to 10%. Such stabilization may reduce, or even eliminate, the effect of stray external fields.