Magnets technical information
The determining of magnetic properties is often not given its proper place along the development path of a product. These basic but important considerations are commonly considered as features which will adapt themselves into 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, with the increased use of rare earth materials, this is no longer the case 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. Only when the magnet is subjected to an external magnetic field of sufficient strength to align the domains can, we say that the magnet has been magnetized. A fully magnetized magnet can be considered as saturated.
To ascertain saturation, it is necessary to apply an external magnetizing field (referred to as the Peak H) of sufficient strength to fully align the domains which exhibit the highest coercivity. The weaker domains will follow. The intensity of the applied field required will depend on the material being used. In general, the Alnico family will require 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 is capable of providing 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 internal 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 maintains the stability of the material and obtains a high degree of consistency in the end-product.