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Rare Earth (RE) Permanent Magnets based on SmCo and NdFeB

Permanent magnets are characterized by the remanence Br (= strength of the magnet) and the coercivity HcJ (= temperature stability / stability against opposing magnetic fields). Permanent magnets based on SmCo and NdFeB  reveal about a factor of 10 higher energy products (BH)max (= stored energy per volume) compared to "conventional" permanent magnets like ferrites and AlNiCo.

RE permanent magnets are produced powder metallurgical by pressing in strong magnetic fields and subsequent sintering. The high (BH)max values are achieved on the one hand by the high amount of metallic, strong magnetic iron or cobalt and on the other hand by the highly anisotropic rare earth elements.

RE permanent magnets are used for multiple applications depending on different aspects of their properties:

  • Highest energy product for miniaturization in application like sensors
  • Highest temperature stability in motors and for automotive applications
  • Highest stability against opposing fields for servo motors

For the characterization of the properties of permanent magnets most commonly a plot of the remanence vs. the coercivity is used. Additionally the maximum application temperature is shown in the diagram below.

VACODYM:

VACODYM® magnets consist predominantely out of two phases - the hardmagnetic (Nd,Dy)2Fe14B phase and a nonmagnetic and ductile Nd-rich phase at the grain boundaries. The coercivity is determined by the amount of Dy, which replaces the Nd in the main phase. With increasing amount of Dy the coercivity is increased, while the remanence is slightly is reduced. By optimizing the composition of Nd-rich boundary phase the corrosion resistance in hot and humid climates could be significantly enhanced. So it is now possible to use uncoated VACODYM magnets in even more applications.

VACODYM 7xx: Nd-Fe-B magnets with highest energy density (= remanence) for applications in linear motors, beam guiding systems (like undulators) and medical technology (like MRI).

VACODYM 8xx: Nd-Fe-B magnets with highest energy density (= remanence) für motors and generators. These alloys show a very high corrosion stability in hot and humid atmospheres.
Depending on the application the coercivity can be adjusted by the right composition (i.e. VACODYM 837 for linear motors, VACODYM 872 for servo motors und VACODYM 890 for hybrid motors in automobiles).

VACODYM 6xx: Standard grade with similar properties concerning the corrosion stability as VACODYM 8xx.


VACOMAX:

This class of Sm-Co based alloys reveals a significantly improved temperature stability of the magnetic properties compared to Nd-Fe-B magnets.

VACOMAX® 225/240: Sm-Co magnets based on Sm2Co17. Because of the extremely high Curie temperature applications of up to 350 °C are possible for these grades. The demagnetization of these types of magnets is based on the "pinning type". Therefore these grades are perfectly suitable for miniature applications, where degradation of remanence due to surface effects is not acceptable.

VACOMAX 145/170/200: Sm-Co Magnete based on SmCo5. Due to the high Curie temperature these grades can be used up to 250 °C. In contradiction to Nd-Fe-B magnets SmCo5 does not contain any iron and therefore does not corrode (rust) in contact with water or water vapor. Therefore SmCo5 magnets will normally not be coated. Since SmCo5 are nucleation type magnets (as Nd-Fe-B) they can be much easier magnetized than VACOMAX 225 magnets.

Last update: 18.03.2016

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