There are five families of magnetic materials. These are, in order of increasing magnetic strength, the Flexible, Ceramic, Alnico, Samarium Cobalt, and Neodymium types. The information below summarizes the properties of each type to help you decide what you might need.
Flexible magnets are a special form of ferrite or rare-earth magnet materials, manufactured by binding ferrite or rare-earth magnet powders in a variety of carriers, such as vinyl.
Ceramic (ferrite) magnets are composed of barium or strontium ferrite, and the most widely used, lowest-cost magnet material available today.
Alnico magnets are composed of aluminum, nickel, and cobalt, and have been popular since the 1930’s. Alnico magnets are used primarily in technical applications, where temperature stability is critical.
Samarium Cobalt magnets are a class of rare-earth magnet materials that were introduced in the early 1970’s. Today, SmCo magnets are most often used in applications that require elevated temperatures and the need for high magnetic properties.
Neodymium magnets are rare-earth magnet materials with the highest magnetic properties. Composed of neodymium, iron & boron, these strong permanent magnets are the most powerful class of magnet materials commercially available today.
In addition to the families noted above, there are various grades within each family. For most non-technical applications, the grade is not terribly important. The magnets shown on the MagnetShop.com site are chosen for economy and for general applications.
The most powerful magnets available today are the Rare Earth types. Of the Rare Earths, Neodymium-Iron-Boron magnets are the strongest. However, at elevated temperatures (of approximately 200 degrees C and above), Samarium Cobalt magnets can be stronger than the Neodymium-Iron-Boron types (depending on the magnetic circuit).
Given a magnet size, you can estimate how much magnetic flux different materials will project at a given distance or you can use this information to compare one material to another.
Example: How much more flux will a Neo 35 project as compared to a Ceramic 5 of the same dimension at a given distance?
Simply divide the Br of Neo 35 by the Br of Ceramic 5 (12,300/3,950) to get 3.1. This means that the Neo 35 would give you 3.1 times the flux a Ceramic 5 the same size would at a given distance. Given a certain flux required at some fixed distance from the magnet, you can use this information to estimate what magnet volume will be required for different magnet materials.
Example: What volume of a Ceramic 5 magnet would give the same flux as a Neo 35 magnet at a given distance?
Simply divide the BHmax of Neo 35 by the BHmax of Ceramic 5 (35/3.6) to get 9.7. This means that the volume of the Ceramic 5 magnet would have to be 9.7 times that of the Neo 35 magnet to give you the same flux.
The maximum temperature that a magnet may be effectively used at depends greatly on the magnetic circuit the magnet is operating in. Shown here are approximate maximum operating temperatures for the various classes of magnet material. At temperatures close to those listed here, special attention may be needed in order to ensure that the magnet will not become demagnetized.