Q
Rare Earth Magnet Properties (Comparison of several types of magnets attached)
A

Some important properties used to compare permanent magnets are: 

  • remanence (Br), which measures the strength of the magnetic field; 
  • coercivity (Hci), the material's resistance to becoming demagnetized; 
  • energy product (BHmax), the density of magnetic energy; and 
  • Curie temperature (Tc), the temperature at which the material loses its magnetism. 


Rare earth magnets have higher remanence, much higher coercivity and energy product, but (for neodymium) lower Curie temperature than other types. The table below compares the magnetic performance of the two types of rare earth magnet, neodymium (Nd2Fe14B) and samarium-cobalt (SmCo5), with other types of permanent magnets.


Magnet Br (T) Hci (kA/m) (BH)max (kJ/m3) Tc (°C)
Nd2Fe14B (sintered) 1.0–1.4 750–2000 200–440 310–400
Nd2Fe14B (bonded) 0.6–0.7 600–1200 60–100 310–400
SmCo5 (sintered) 0.8–1.1 600–2000 120–200 720
Sm2Co17 (sintered) 0.9–1.15 450–1300 150–240 800
Alnico (sintered) 0.6–1.4 275 10–88 700–860
Sr-ferrite (sintered) 0.2–0.4 100–300 10–40 450

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