A review is given of the formation, the crystal structure and the magnetic properties of several classes of rare earth based intermetallic compounds that lend themselves as starting materials of permanent magnets. These compounds include R2Fe14B, R2Fe14C and R2Co14B and the large class of ternary rare earth compounds having the tetragonal ThMn12 structure. Special emphasis is given to the changes in magnetic properties of R2Fe17 compounds observed after interstitial solution of C or N atoms. The magnetic properties of all these compounds are discussed in terms of current models based on intersublattice and intrasublattice exchange and the interplay between the rare earth sublattice anisotropy and 3D sublattice anisotropy. A substantial portion of the review is devoted to manufacturing routes of permanent magnets and a description of the coercivity mechanisms operative in the magnets. A comparison is made of the performance and economic costs of various types of magnets and novel applications are briefly discussed.

https://iopscience.iop.org/article/10.1088/0034-4885/54/9/001/pdf

New developments in hard magnetic materials

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

The structure of thin, aggregated layers of CuS nanoparticles, grown in Langmuir−Blodgett film precursors, was investigated with atomic force microscopy along with the study of their electrical conductivity. Very thin layers revealed an essentially insulating behavior. These layers were composed of isolated particle aggregates that had a mean thickness corresponding to the average particle diameter. The increase of the film thickness resulted in the formation of conducting pathways formed by the aggregates in the layer plane. Such samples revealed an increased conductivity. Finally, when the thickness of the initial precursor LB layers was more than 25 bilayers, the resulting aggregated films were uniform and their electrical conductivity was high.

Microstructure origin of the conductivity differences in aggregated CuS films of different thickness

Chapter 4 Magnetism and processing of permanent magnet materials

A new stable compound in the Nd–Fe system has been identified as Nd5Fe17. The crystal structure belongs to the hexagonal space group P63/mcm, with a=2.0214(8) nm and c=1.2329(8) nm, and with 12 formula units per unit cell. This compound is a ferromagnet with Tc = 503 K and magnetization 162 emu/g at 4.2 K. Mossbauer spectra have been measured and fitted with five Fe sites, yielding an average Beff=26.5 T at room temperature, from which an average Fe moment of 1.83 Bohr magnetons is deduced. X‐ray powder diagrams from magnetically aligned samples suggest basal anisotropy.

Magnetic and structural characterization of Nd5Fe17

A new stable phase in the NdFe system has been identified. X-ray diffraction examination of single crystals was used to establish the crystal structure of Nd5Fe17. The hexagonal space group is P6 3 mcm and the lattice parameters are a = 2.0214(8) nm, c = 1.2329(8) nm, Z = 12. The Nd5Fe17 structure is built up of layers which are a tessellation of triangles, pentagons, hexagons and heptagons. The stacking of layers forms antiprisms. Clusters of neodymium atoms only are made of trigonal antiprisms or regular octahedra stacked upon each other to form infinite columns. Each neodymium cluster is surrounded by a first ring of nine pentagonal antiprisms centred by iron atoms and a second ring of 12 antiprisms with hexagonal and heptagonal faces centred by neodymium atoms.

A new phase in the NdFe system: Crystal structure of Nd5Fe17

X-ray diffraction on single crystals was used to establish the crystal structure of YCo 3 Ga 2 and YNi 3 Ga 2 . This hexagonal structure belongs to the P 6/ mmm space group. RCo 3 Ga 2 compounds with R ≡ La — Er and RNi 3 Ga 2 with R ≡ La — Tm crystallize with the same structure which is closely related to the hexagonal CaCu 5 -type structure.

RM3Ga2 Compounds (R ≡ rare earth, M ≡ Co, Ni): A new structural series

X-ray diffraction studies of single crystal YRh2Si were used to establish the crystal structure, with space group P6/mmc and lattice parameters a = 5.495 A, c = 15.030 A. YRh2Si with CeNi3-type structure is a member of the Rn +2 T3n +3M2n + 1 structural series (n = 1) with intergrown Mg2Cu3Si-type and CeCo3B2-type slabs.

Structure of YRh2Si: An ordered CeNi3 type

Magnetic structures of Nd2Fe2Si2C and Tb2Fe2Si2C

X-ray diffraction studies of single crystal DyFe2SiC were used to establish the crystal structure, with space group Cmcm and lattice constants a = 3.712(0) A , b = 10.531(3) A , c = 6.863(1) A . The crystal structure is derived from the YNiAl2 type (Re3B-type derivative) with an ordered replacement of aluminium atoms by iron atoms and of nickel atoms by silicon atoms and with an addition of carbon atoms between the infinite columns of silicon centred DyFe2 prisms.

L. Paccard

Papers

A new phase in the NdFe system: Crystal structure of Nd5Fe17

RM3Ga2 Compounds (R ≡ rare earth, M ≡ Co, Ni): A new structural series

Structure of YRh2Si: An ordered CeNi3 type

Magnetic structures of Nd2Fe2Si2C and Tb2Fe2Si2C

A new quaternary iron-rich phase stabilized by carbon: DyFe2SiC