Magnet Information and Selection
In general magnet information, there are four families of magnets available commercially. Factors such as operating temperature, demagnetizing effects, field strength, environmental characteristics, and available space for movement need to be considered before selecting a magnet for a reed switch or reed sensor application. An overview of each of the families of magnets is given below. A list of our standard magnets is available here.
NdFeB
An NdFeB, or Neodymium Iron Boron magnet, is a type of rare earth magnet which is one of the strongest available commercially.
- Highest energy product
- Very high remanence and coercivity
- Relatively low priced
- Mechanically stronger
- Some grades can be used up to 200°C
- Not recommended in Hydrogen atmosphere
- Bonded types can be machined but not tapped
SmCo
An SmCo or Semarium Cobalt magnet, it a also a type of rare earth magnet which is not as strong as NdFeB magnets but can withstand higher temperatures.
- High energy product
- Suitable for high performance applications
- High resistance to demagnetization
- Excellent thermal stability
- High corrosion resistance
- Most expensive magnet
- Can be used up to 300°C
- Prone to chipping – should not be used as a structure
AlNiCo
An AlNiCo or Aluminum Nickel Cobalt magnet, is a type of magnet have high coercivity, or resistance to loss of magnetism.
- Cheaper than rare earth magnets
- Highest working temperature of 550°C
- Lowest temperature coefficient
- Low coercivity when compared to other types
High induction levels
Ferrite (Ceramic)
A Ferrite or Hard Ferrite ceramic magnet, is a type of magnet that is electrically non-conductive and generally low cost permanent magnets.
- Brittle
- Poor thermal stability
- Cheapest of all types
- Can be used up to 300°C
- Needs grinding to meet tight tolerances
- High corrosion resistance
Magnet Selection Guide
Depending on what a reed switch or reed sensor application demands, we have tabulated magnet information and the properties of the four types of magnets in increasing order of magnitude. The most important property required should be looked at first and then subsequent ones, to get best results.
| Low | High | |||
| Cost | Ferrite | AlNiCo | NdFeB | SmCo |
| Energy | Ferrite | AlNiCo | SmCo | NdFeB |
| Operating Temperature | NdFeB | Ferrite | SmCo | AlNiCo |
| Corrosion Resistance | NdFeB | SmCo | AlNiCo | Ferrite |
| Resistance to Demagnetization | AlNiCo | Ferrite | NdFeB | SmCo |
| Mechanical Strength | Ferrite | SmCo | NdFeB | AlNiCo |
| Temperature Coefficient | AlNiCo | SmCo | NdFeB | Ferrite |
Units Conversion Table
| Property | CGS Unit | SI Unit | Conversion Factor |
| Magnetic Flux | Maxwell | Weber | 1 Weber = 108 Maxwell |
| Magneto-motive Force | Gilbert | Ampere-Turn | 1 AT = 1.256 Gilbert |
| Magnetic Flux Density (B) | Gauss | Tesla | 1 Tesla = 104 Gauss |
| Magnetic Field Strength (H) | Oersted | Ampere-Turn/Meter | 1 AT/m = 0.0125663 Oersted |
| Magnet Performance (BHmax) | MGOe | Kilo-Joules/Meter3 | 1MGOe = 7.957 KJ/m3 |