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Magnet Types

Ferrite or Ceramic Magnets

Ferrite Magnets or Ceramic Ferrite Magnets are manufactured from strontium ferrite, usually die pressed and sintered. Sintering is when a mass of metal particles bonded and partly fused by the use of pressure and heat below the melting point. Due to good machining properties, these magnets can be cut and magnetized to virtually any size or shape required. Due to their high coercively and low cost, they are used in a wide range of applications. Stable up to a maximum temperature of 120°C, by weight they are stronger than steel, but less so than neodymium or Rare Earth Magnets. Like all ceramics, they are quite brittle and will easily break if dropped onto a hard surface. They are the most economical choice for magnetic strength.

These magnets are also made in different grades. Ceramic-1 is an isotropic grade with equal magnetic properties in all directions. Ceramic grades 5 and 8 are anisotropic grades. Anisotropic magnets are magnetized in the direction of pressing. The anisotropic method delivers the highest energy product among ceramic magnets at values up to 3.5 MGOe (Mega Gauss Oersted). Ceramic magnets have a good balance of magnetic strength, resistance to demagnetizing and economy. They are the most widely used magnets today.

Ferrite magnets are generally the best choice for doing repulsion and attraction experiments since some of the rare earth magnets may be too strong and bar magnets will demagnetize. Ferrites come in blocks/slabs, disks and rings.

Attributes of Ceramic Magnets

High intrinsic coercive force.
Least expensive material compared to alnico and rare earth magnets.
Limited to simple shapes due to manufacturing process.
Lower service temperature than alnico, greater than rare earth.
Finishing requires diamond cutting or grinding wheel.
Lower energy product than alnico and rare earth magnets.

Rare Earth Magnets or Neodymium Iron Boron Magnets

Neodymium Magnets or Rare Earth are manufactured from sintered neodymium iron boron. They possess the most powerful magnetic properties in relation to volume and can lift up to 1000 times their own weight. However they do not possess strong heat resistant qualities usually remaining stable up to 80°C, although SH grades of the compound are available which are stable up to 120°C. For higher temperature applications, rare earth samarium cobalt is recommended. Also due to their corrosive nature, neodymium is usually supplied nickel coated. These magnets are magnetized through their thickness, and are often used when space is limited and you need a lot of sticking power. Neodymium Magnets or Rare Earth Magnets can be used for demonstrating attraction and repulsion, for science, engineering, research & development, education, industry and magic, but the larger ones are exceptionally strong and should be used with caution.

Neodymium Magnets or Rare Earth Magnets are available in disks, slabs/blocks and rings.

What is the difference between Ferrite Magnets and Rare Earth or Neodymium Magnets?

The biggest differences between ferrite magnets and rare earth magnets is that rare earth magnets are much stronger. The intensity of magnetization and the coercive force are elements determining the performance of permanent magnets. Since rare earth magnets contain iron and cobalt in the state not containing oxygen, their magnetization is large. In addition, magnetization of rare earth magnets has a strong force (coercive force) aligning the magnetism in one direction, so they are much stronger magnets than ferrite magnets. Since they have about 7 times the performance of ferrite magnets in total energy per volume, rare earth magnets are used for powerful magnetic circuits that could not be conceived of until now, space-saving magnetic circuits, etc.

What are the primary applications for Rare Earth or Neodymium Magnets?

The primary application, for rare earth magnets, is the voice coil motors that are a part of computer hard disk drives. Other applications include various industrial motors, sensors, consumer electronics, office equipment, musical instruments, and cellular phones. Recently, rare earth magnets have been used in products that help protect the environment and save energy such as electric vehicle motors, wind powered generators, and air conditioner compressors.

Attributes of Rare Earth or Neodymium Magnets

Very high resistance to demagnetization
High energy for size
Good in ambient temperature
Moderately priced
Material is corrosive and should be coated for long term maximum energy output
Low working temperature for heat applications, but higher levels of heat resistance materials are being introduced periodically.

Bar & Horse Shoe Magnets

Bar Magnets are used in physics education labs to show magnetic fields when used with compasses, iron filings or light metal objects such as paper clips. If a bar magnet or horseshoe magnet is stored properly, with its keepers, it can have a shelf life of at least 20 years.

Flexible Magnets

Flexible magnets are very similar to the injection molded magnets but are produced in flat strips and sheets. These magnets are lower in magnetic strength and very flexible depending on the materials that was used in the compound with the magnetic powders. Vinyl is often used in this type of magnet as the binder.

This page was last updated on Thursday, 05 November 2009