Q: How permanent is a permanent magnet?
A: The ability of a permanent magnet to "hold" a magnetic field results from "locked-in" positions of small magnetic domains within the magnet itself. For practical purposes, if magnetized properly, a permanent magnet will maintain all of its magnetism unless acted upon by external forces. In the absence of these forces, a permanent magnet will not lose any more than 2% of it's magnetism over a 100 year period. Forces that can demagnetize a permanent magnet are:

• Temperature (heat)

• Opposing external magnetic fields from another magnet, or an electromagnetic field.

• Vibration or Shock (although these factors have little or no effect in most applications).

Q: What is a "rare earth" magnet?
A: A rare earth magnet is a permanent magnet that is manufactured using one of the "rare earth" elements. Rare earth magnets are the most powerful magnets commercially available in the world today. The rare earth elements (elements 57-71) have striking similarities, and have been identified as a family on the Periodic Table of Elements. The most common rare earth magnets contain samarium (samarium- cobalt), and neodymium (neodymium-iron-boron). Commercial magnets are also available, although not as common, containing Cerium and Praseodymium. 

Q: What is the "most economic" magnet material? 
A: This is a tricky question! The obvious answer is that ceramic is the most cost effective material in terms of lowest price per pound (then Alnico, Neodymium-Iron Boron, and finally Samarium Cobalt). But the reality is that often the more expensive rare earth materials can be more economical, as due to their high energies and coercive force properties, the amount of material required can be dramatically reduced. The proper answer (not a cop out) is that it depends on the application. At MagStar, our applications engineers can assist you in determining the most economical material for your application. 

Q: How do I know which type of material to use for my application? 
A: Choosing a material sometimes involves eliminating materials based on material properties. For example;

• Will the magnet be exposed to elevated temperatures? Neodymium-Iron-Boron materials will demagnetize (irreversible losses) above 150 degrees Celsius. 

• How much space do I have for the magnet? What is the envelope (profile) where the magnet needs to fit? Alnico magnets typically need long magnetic lengths in relation to the cross sectional area. If space is limited or the profile is small, rare earth magnets work very well.

• What environment will the magnet be placed in? Neodymium magnets oxidize (rust) due to the high content of iron in the material. Plating or coating a neodymium magnet is always recommended, but even so is not always enough to prevent corrosion of the magnets.

• Will the magnet see demagnetizing forces (temperature, back EMF, electromagnetic fields, or a field from another magnet)? Then a magnet material with a high coercive force and/or high operating temperatures would be required.

Our applications engineers can assist you in selection of the material that is best for your application. There are obviously many factors that influence material selection. The more specific information you have (i.e. gauss, force requirements, air gap, etc) the quicker we can assist you in the choice of the best possible material for your application. MagStar Technologies maintains extensive inventories of the best materials from around the world. We have no biases toward a particular manufacturer, or material - just a bias to helping you select the best material for your application. Please contact us today!

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