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

Permanent magnet materials based on tetragonal rare earth compounds of the type RFe12−xMx

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

Intrinsic hard magnetic properties of Sm(Fe1 − xCox)12 compound with the ThMn12 structure

We succeed in inserting a number of nitrogen atoms into the RTiFe11 intermetallics. The nitrides retain the ThMn12‐type structure, but with an increase in the unit cell volume. The crystallographic sites located by nitrogen atoms are determined by using neutron diffraction techniques. The nitrogen atoms are found to have an effect of increasing Curie temperature and saturation magnetization. Moreover, an essential change in magnetocrystalline anisotropy is observed upon nitrogenation. By all of these effects, the NdTiFe11N1−δ compounds have excellent intrinsic magnetic properties favorable for permanent magnet applications.

Magnetic and crystallographic properties of novel Fe‐rich rare‐earth nitrides of the type RTiFe11N1−δ (invited)

We have discovered that the rare‐earth–iron intermetallics of the type RTiFe11 can absorb moderate quantities of nitrogen at 500 °C, giving the approximate composition RTiFe11N0.5 at 1 atm. X‐ray diffraction showed that the tetragonal structure (I4/mmm) is retained but that the unit cell volume is slightly increased. More significantly, profound change of magnetocrystalline anisotropy have occurred upon the absorption of nitrogen. In this letter, we report the lattice parameters and magnetocrystalline anisotropic properties of RTiFe11Nx compounds.

Magnetocrystalline anisotropies of RTiFe11Nx compounds

New potential hard magnetic material-ndtife11nx

Neutron diffraction study of the nitride YTiFe11Nx

We succeed in stabilizing the PrMo1.5Fe10.5 compounds and their nitrides with ThMn12‐type structure. The single phase was identified by using x‐ray diffraction technique and thermomagnetic measurements. In PrMo1.5Fe10.5Nx, the c‐axis is the easy magnetization direction from 0 K to Curie temperature. The anisotropy field is up to 147 KOe at 1.5 K and 110 KOe at room temperature. In combination with a high Curie temperature of 640 K and a large saturation magnetization of 141.70 emu/g, these intrinsic magnetic properties are favorable for permanent magnet applications. As a preliminary attempt, a coercive force of 3.0 and 10.0 KOe was obtained at 300 and 1.5 K, respectively, by using hydrogenation disproportionation and desorption (HDD) processing.

Xiao-dong Zhang

Papers

Magnetocrystalline anisotropies of RTiFe11Nx compounds

New potential hard magnetic material-ndtife11nx

Neutron diffraction study of the nitride YTiFe11Nx

Formation and characteristics of hard magnetic materials: Pr(Mo,Fe)12Nx

Neutron diffraction study of Y2Fe14BN1−δ