After the development of Nd–Fe–B magnets, rare-earth magnets are now essential components in many fields of technology, because of their ability to provide a strong magnetic flux. There are two, well-established techniques for the manufacture of rare earth magnets: powder metallurgy is used to obtain high-performance, anisotropic, fully dense magnet bodies; and the melt-spinning or HDDR (hydrogenation, disproportionation, desorption and recombination) process is widely used to produce magnet powders for bonded magnets. In the industry of sintered Nd–Fe–B magnets, the total amount of production has increased and their dominant application has been changed to motors. In particular, their use for motors in hybrid cars is one of the most attractive applications. Bonded magnets have also been used for small motors, and the studies of nanocomposite and Sm–Fe–N magnets have become widespread. This paper reviews the current status and future trend in the research of permanent magnets.

https://iopscience.iop.org/article/10.1088/0022-3727/44/6/064001/pdf

Current status and recent topics of rare-earth permanent magnets

http://www.contrib.andrew.cmu.edu/~dl0p/laughlin/pdf/248.pdf

Nano-scale materials development for future magnetic applications

Permanent magnet development has historically been driven by the need to supply larger magnetic energy in ever smaller volumes for incorporation in an enormous variety of applications that include consumer products, transportation components, military hardware, and clean energy technologies such as wind turbine generators and hybrid vehicle regenerative motors. Since the 1960s, the so-called rare-earth “supermagnets,” composed of iron, cobalt, and rare-earth elements such as Nd, Pr, and Sm, have accounted for the majority of global sales of high-energy–product permanent magnets for advanced applications. In rare-earth magnets, the transition-metal components provide high magnetization, and the rare-earth components contribute a very large magnetocrystalline anisotropy that donates high resistance to demagnetization. However, at the end of 2009, geopolitical influences created a worldwide strategic shortage of rare-earth elements that may be addressed, among other actions, through the development of rare-earth-free magnetic materials harnessing sources of magnetic anisotropy other than that provided by the rare-earth components. Materials engineering at the micron scale, nanoscale, and Angstrom scales, accompanied by improvements in the understanding and characterization of nanoscale magnetic phenomena, is anticipated to result in new types of permanent magnetic materials with superior performance.

Perspectives on Permanent Magnetic Materials for Energy Conversion and Power Generation

Existence range, structural and magnetic properties of Nd3Fe27.5Ti1.5−yMoy and Nd3Fe27.5Ti1.5−yMoyNx (0.0 ≤ y ≤ 1.5)

Structural properties of a novel magnetic ternary phase: Nd3(Fe1−xTix)29 (0.04 ≤ x≤ 0.06)

New rare‐earth (R), iron‐rich ternary intermetallic compounds of the form R3(Fe,M)29 with the monoclinic Nd3(Fe,Ti)29 structure (space group P21/c, ♯14, Z=2) have recently been shown to form with R=Ce, Nd, Pr, Sm, and Gd, and M=Ti, V, Cr, and Mn. This novel structure is derived from the alternate stacking of Th2Zn17 and ThMn12‐type segments and contains two R sites and fifteen Fe(M) sites. Reported Curie temperatures of the 3:29 compounds range from 296 K (R=Ce, M=Cr) to 524 K (R=Sm, M=V). The 3:29 compounds all show improved magnetic properties after interstitial modification with H or N; in particular, room‐temperature coercivity has been reported in Sm3(Fe,Ti)29N5, making this compound a candidate for possible permanent‐magnet applications. In this article we will review the work carried out to date on the 3:29 compounds.

New rare‐earth intermetallic phases R3(Fe,M)29Xn: (R=Ce, Pr, Nd, Sm, Gd; M=Ti, V, Cr, Mn; and X=H, N, C) (invited)

Alloys with the composition Nd2(Fe,Ti)19 can exist in two crystal structures depending on the preparation technique. Melt‐spun material has a hexagonal TbCu7‐type structure (a=4.902 A, c=4.248 A) for a range of quenching speeds. Alloys prepared by arc melting, annealing at 1373 K and then water quenching have a complex monoclinic structure derived from a TbCu7 superlattice (a=10.644 A, b=8.585 A, c=9.755 A, β=96.92°) and related to those of other intermetallics such as tetragonal Nd(Fe,Ti)12 and rhombohedral Nd2Fe17. Magnetic ordering temperatures for annealed (monoclinic) and melt‐spun (hexagonal) Nd2(Fe,Ti)19 are 411 and 454 K, respectively. 57Fe Mossbauer spectroscopy at 295 K demonstrates that the local environments of the Fe atoms in the two structural modifications of Nd2(Fe,Ti)19 are similar. The average 57Fe magnetic hyperfine fields at 295 K for the monoclinic and hexagonal Nd2(Fe,Ti)19 are 20.8 and 22.3 T, corresponding to average Fe magnetic moments of 1.33 and 1.43μB, respectively.

R. L. Davis

Papers

Structural properties of a novel magnetic ternary phase: Nd3(Fe1−xTix)29 (0.04 ≤ x≤ 0.06)

New rare‐earth intermetallic phases R3(Fe,M)29Xn: (R=Ce, Pr, Nd, Sm, Gd; M=Ti, V, Cr, Mn; and X=H, N, C) (invited)

Structural and magnetic properties of Nd2(Fe,Ti)19

New Rare-Earth Intermetallic Phases R3(Fe,M)29Xn: (R: Ce, Pr, Nd, Sm, Gd; M: Ti, V, Cr, Mn; and X : H, N, C)