Rapidly quenched isotropic rare earth iron boride (RE–Fe–B) powders have found many applications throughout the electronics, automotive and white goods industries. The magnetic performance, thermal stability, corrosion resistance and processability of a powder are important factors when selecting a RE–Fe–B powder for a particular application. For electronic devices that operate at ambient temperatures, high remanence (Br) tends to be a priority and RE2Fe14B/α-Fe nanocomposite powder magnets are favoured. Alternatively, automotive applications tend to require greater thermal stability and corrosion resistance, which are satisfied by single-phase RE2Fe14B powder magnets with higher intrinsic coercivity (Hci). This article reviews the performance of commercially available rapidly solidified RE–Fe–B powders and recent developments made to address the demands of applications.

The microstructure and magnetic properties of melt-spun RE2Fe14B/alpha-Fe and RE2Fe14B/Fe3B nanocomposite powders; were studied using Pr and Nd versions of RE9Fe86B5(RE2Fe14B/alpha-Fe) and RE9Fe79B12(RE2Fe14B/Fe3B) alloys. It was found that the RE9Fe86B5 exhibited a finer and more uniform microstructure with an average grain size of similar to 10 nm, whereas a relatively coarse microstructure (grain size up to 100 nm) was observed in the RE9Fe79B12. It was also found that the RE9Fe86B5 yielded higher B-r and (BH)(max), and a more square demagnetization loop, although the H-ci was slightly lower. The superior magnetic properties observed in the RE9Fe86B5 can be attributed to the more favorable intrinsic magnetic properties of alpha-Fe (higher M-s and lower K) and the much finer microstructure, which produces a stronger intergrain exchange coupling between the RE2Fe14B and alpha-Fe phases. The results indicate that RE2Fe14B/alpha-Fe nanocomposites are more desirable than RE2Fe14B/Fe3B for future development of RE-Fe-B nanocomposite magnets.

Hot deformed magnets can be commercially produced from hyper-stoichiometric nanocrystalline Nd-Fe-B compositions. This paper summarizes the influence of the rare-earth component (Nd, Pr, Dy) and gallium to magnetic properties and hot workability of die-upset magnets based upon hyper-stoichiometric compositions. Increasing the Nd from 13.3 to 14.4 at.% raises the H/sub ci/ from 770 to 930 kAm/sup -1/. B/sub r/ values are highest (1.31 T) at lower levels of RE (/spl sim/13 at.%), although such compositions exhibit a decrease in hot workability. The substitution of Dy and Pr for Nd promotes higher H/sub ci/ values at some expense in B/sub r/. Gallium additions up to 0.5 at.% significantly increase both B/sub r/ and H/sub ci/.

This paper presents an application of the finite-element method codes developed to design the magnetizing fixtures for isotropic magnets when in situ magnetization is required. The radial, pseudoradial, and multipole magnetization of the surface mounted and interior magnet assemblies are considered. On several case studies, it is demonstrated how accurate modeling of magnetization can be effectively employed for design of permanent-magnet assemblies.

The paper describes a finite-element solver capable to simulate a pulse magnetization of anisotropic permanent magnets and magnet assemblies. A simplified vector hysteresis model of the anisotropic magnet material is presented. The solver has been validated using analytical solutions and experimental flux profiles measured at the surfaces of cylinders and rings in the open and closed magnetic circuits. Several case studies are given to illustrate benefits of the solver in design and optimization of the magnetizing fixtures when a full saturation, shaping or skewing of magnetic poles is required.

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.

An improved model of the isotropic permanent magnet is presented. The model uses different portions of the hysteresis loop in orthogonal directions. The model can predict fairly well the small and mid-range angles of rotation of the magnetization vector when the direction of magnetizing field changes in time