Magnets Technical Information

Determining magnetic properties is often not given its proper place along the development path of a product. These basic but essential considerations are commonly considered as features that will adapt themselves to the required format at a later date. This may be true for applications using low coercive materials such as Alnico or certain Ferrite types. However, this is no longer the case with the increased use of rare earth materials since they are more difficult to magnetize. Increasing sophistication in product design is another factor influencing this and making the preselection of magnets more essential.

Within the physical boundaries of any permanent magnet, there are many microscopic particles called domains. Each of these has a north and a south pole, but they exhibit a random orientation which results in no measurable magnetic field. We can only say that the magnet has been magnetized when the magnet is subjected to an external magnetic field of sufficient strength to align the domains. A fully magnetized magnet can be considered saturated.

To ascertain saturation, it is necessary to apply an external magnetizing field (referred to as the Peak H) of sufficient strength to align the domains that exhibit the highest coercivity fully. The weaker domains will follow. The intensity of the required applied field will depend on the material used. In genThe Alnico family will generally be 3,000 to 8,000 oersteds (Oe), the ferrites 10,000 to 14,000 Oe, and the rare earths 20,000 to greater than 50,000 Oe. A properly saturated magnet can provide the flux levels and resistance to demagnetization indicative of its particular magnet material. If full saturation is not ensured, the magnet will be more susceptible to demagnetization from both ial and external influences. If a magnet is to be used at a level below saturation, it must be fully magnetized and then subjected to a secondary process of controlled demagnetization or conditioning. Only through this process can one maintain the material’s stability and obtain a high degree of consistency in the end product.