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Magnetic Field Strength vs. Material Type

The magnetic field strength (or flux density) of different types of magnets is measured by the residual magnetic field, denoted by “Br”, which is the magnetic field remaining after the magnetization process. 


Magnetic field strength is expressed in Tesla (T) or Gauss (S). 1 Tesla (1T) is equal to 10,000 Gauss. Tesla can also be expressed in SI kilograms per Ampere second squared, i.e. T = kg/As2. 


The most common type of magnetic material is iron oxide (ferrite). It can be made into a hard ferrite by sintering it at high temperatures with other compounds such as barium or strontium carbonate. These magnets are the least expensive and have a lower magnetic field strength of 200mT to 400mT. Bonded or “injection molded” ferrite further reduces the magnetic field strength. Bonded ferrites of the same size and volume as sintered magnets have field strengths between 100mT and 200mT.   


Rare-earth neodymium or samarium cobalt magnets are popular because they offer higher field strengths in a smaller volume, and these sintered magnets can offer remanent magnetism from 900mT to 1,400mT. These Br values are usually halved if the magnet is molded by bonding, and the table below summarizes the strengths of the most common types of magnets and their associated properties.


Comparison and properties introduction of 5 types of magnetic materials

Type

Brief Introduction

Residual Magnetism Range

Temperature Range

Advantages

Disadvantages

Ceramic Ferrite

Sintering iron oxide (Fe2O2) and other metallic elements together at high temperatures

0.2 to 0.45 T

200-300℃

Lower cost and most widely used

Low magnetic field strength, need to be close to the sensor

Sintered Ndfeb

Praseodymium, iron and boron sintered together. Also known as “rare earth” magnets.

1.0 to 1.4 T

80-200℃

Very high strength/size ratio

Significant high temperature attenuation, higher cost than ferrite

Sintered Samarium Cobalt

Samarium and cobalt are sintered together to make another “rare earth” magnet.

0.9 to 1.2 T

250-350℃

Higher maximum working temperature than neodymium, higher demagnetization impact strength

Higher cost and weaker magnetic properties than sintered NdFeB.

Bonded Ferrites

Ferrite powder is mixed with binder and then molded by molding.

0.1 to 0.25 T

120-150℃

Low cost, easy to machine complex shapes

The magnetic field strength is extremely low and requires a very small air gap with the sensor.

Bonded Neodymium

NdFeB powder is mixed with binder and then molded by molding.

0.3 to 0.75 T

120-150℃

Lower cost than sintered NdFeB; suitable for larger diameter rings or multi-pole rings.

Not easy to process complex shapes


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