The comparison of anisotropic (and isotropic) powders for polymer bonded rare earth permanent magnets

Anisotropic rare-earth permanent magnetic powders offer the ability to produce high-energy bonded magnets. Currently, Hydrogenation-Disproportionation-Desorption-Recombination (HDDR) Rare-Earth Iron Boron (RE-Fe-B) and Samarium Iron Nitride (Sm-Fe-N) type powders are available in the marketplace. Recently, an alternative technique for producing anisotropic powder has recently been announced, which can produce RE-Fe-B powder with exceptional magnetic properties and thermal stability. This novel technique involves the hot plastic deformation of melt-spun RE-Fe-B particles. One high energy product version of this powder can produce compression molded bonded magnets with (BH)(max) = 22 MGOe (176 kJ/m(3)) in a preferred orientation at room temperature. Another type of hot deformed powder can produced bonded magnets that exhibit total irreversible flux losses of less than 2% following an aging trial at 125degreesC for 100 hours in air. Equivalent REFe-B HDDR magnets suffered over 15% loss and Sm-Fe-N magnets suffered over 6% loss under the same aging test regime. This study has compared the magnetic properties and thermal stability of such anisotropic bonded magnets with some recently developed isotropic bonded magnets. It is demonstrated that HDDR type magnets have poor thermal stability and demagnetization loop squareness. It is also shown that hot deformed RE-Fe-B powder, and SmFeN material to a limited extent, offer great potential for anisotropic bonded magnets. The greatest thermal stability was observed in an MQP(TM)-14-12 isotropic bonded magnet sample with an uniform nano-scale microstructure.