Part No. Size Grade Pull (kg) Quantity
HS-Button-9 25mm dia x 16mm Alnico 2 2.95kg Pack of 1 Magnet
Alnico does has a low coercive force. This means that it is easily demagnetized by external demagnetising fields. It is therefore possible to magnetise the magnet when part of an assembly (providing the means to magnetise is possible). The Alnico may also self demagnetize. This depends on the total magnetic circuit but an example may be removing an Alnico magnet from a motor assembly for inspection and then placing it back and discovering the magnetic output has fallen. Putting the Alnico magnet in open circuit may be enough to cause self demagnetisation (the working point is taken beyond the ‘knee’ of the Intrinsic curve, causing demagnetisation). The working point is changed if the magnetic circuit changes. Self demagnetisation occurs because the magnetic field from the magnet can pass back through the magnet itself (the magnetic path is more preferable than the air surrounding the magnet), which is thus an external demagnetising field applied by the magnet itself (all magnets in free space will apply a self–demagnetising field but only magnets with very low working point and/or a low Hci values will show demagnetisation as a result of it). Rare Earth magnets (NdFeB and SmCo) and ferrite magnets, in normal operation, do not demagnetise by self demagnetisation. Alnico (and indeed all magnets) is better at resisting self demagnetisation by being longer in the direction of magnetisation than in the other dimensions (usually termed Length to Diameter, L/D, ratio) as this increases the working point on the Intrinsic curve. An L/D ratio of at least 4 or 5 is considered a better design for Alnico. This is why Alnico magnets are very rarely short in length. For note, most BH curves for Alnico show a single curve, often the Normal curve. This is because the Intrinsic curve is deemed to be similar to the Normal curve but, to be accurate, the Intrinsic curve is the only curve to be used to determine demagnetisation effects (you may be able to use the Normal curve for crude analysis on Alnico but use of the Normal curve with any other magnet material will give incorrect results).
