Rare Earth Magnets

The value in rare earth magnets is their magnetic qualities, not the common materials from which hey are made. These magnets were developed in the 1970s and 1980s and have proven to be the strongest type of permanent magnets available. Magnets are rated by four different properties; their value depends upon the strength of the magnetism and how long it lasts. Two kinds of man-made magnets are widely used today because of these special properties. These are Samarium-cobalt and Neodymium.

The four properties used to compare permanent magnets are remanence (the strength of the magnetic field), coercivity (ability to stay magnetized), energy product (density of the magnetic energy) and Curie temperature (temperature at which the magnetism is lost). Although Samarium-cobalt and Neodymium are more expensive, they are the strongest and longest lasting magnets on the market. Samarium-cobalt is the most expensive but retains its magnetic properties to a higher temperature, 720?F.  Neodymium begins to lose its magnetic qualities around 310 to 400?F.


 The elements called rare earth metals are metals that can be magnetized, like a rare earth magnet. This has to do with the electrons and other components of the crystalline structure.





These minerals are as abundant as lead. Combining these with other metals like cobalt, nickel and iron in a costly and complicated process is necessary to produce these permanent magnets. For example solid pieces of Neodymium and other metals must be ground into a very fine powder, the size a few microns in diameter. This is pressed firmly into a mold and magnetized. This block is very carefully heated in a sintering furnace to about 1000?C that allows the Neodymium to melt.

These magnets have some built-in problems. The magnets are extremely brittle and will corrode easily. Chipping, cracking and fracturing are common problems requiring careful handling. The corrosion issue was addressed by coating the magnets with different metals and even an epoxy resin. The specific use determines what covering is used; zinc, nickel, tin and gold are common choices. Even more of a problem is their strength. People can become injured if they are trapped between two magnets only a few centimeters in size. These injuries can be pinched skin or even broken bones. If the magnets are allowed to get too close to each other they smash together with enough force to break the brittle material and send flying pieces everywhere.

These wonderful rare earth magnets provide a long-lasting, powerful magnetic field and are used in many industries to make life easier for people. The name rare earth magnet comes from the unique properties the minerals have of allowing themselves to be magnetized.