Publisher Summary This chapter describes the interstitially modified intermetallics of rare earth and 3D elements. The discovery that metastable intermetallic compounds can be produced by a process of gas-phase interstitial modification has significantly widened the range of rare earth intermetallics with intrinsic magnetic properties suitable for use as permanent magnets. To have a sufficiently high magnetic hardness and a reasonable temperature stability, high magnetization and high Curie temperature are essential for new materials suitable for permanent magnet applications. The intrinsic magnetic properties at room temperature for some well known permanent magnet materials are also discussed in the chapter. Permanent magnets with different levels of ( BH )max have their own market according to different requirement in various kinds of applications. The main contribution to the magnetic anisotropy in permanent magnet materials is the crystal-field induced single-ion anisotropy on the magnetic rare earth-atoms. The 4f moment of the rare-earth atoms will prefer a certain magnetization direction that is determined by the properties of the rare-earth atoms and the crystal electric field at the particular crystallographic sites.

Chapter 3 Interstitially modified intermetallics of rare earth and 3D elements

Stabilizing the 1‐12 phase with cerium was possible using a special heat treatment. The structural and magnetic properties of Ce(Fe,M)12 and their nitrides, for M=Ti, V, Cr, Mo, etc., were investigated using x‐ray‐diffraction and magnetic measurements. The effects of interstitial nitrogen atoms on lattice parameters, Curie temperature, saturation magnetization, and magnetocrystalline anisotropy are reported. A profound change was found on the magnetocrystalline anisotropy. As an example, in the case of CeMo2Fe10Nx, the easy magnetization direction changes from c axis to the basal plane depending on the nitrogen content x.

Structural and magnetic properties of Ce(Fe,M)12Nx interstitial compounds, M=Ti, V, Cr, and Mo

The hard magnetic properties of nitrided melt-spun R(Fe,M)12 (R=Pr and Nd, M=V and Mo) ribbons have been investigated Hard magnetic powders were prepared by vacuum annealing of ground ribbons in the temperature range from 700 to 950 °C and subsequent nitrogenation For NdFe105Mo15Nx and PrFe105Mo15Nx powders, coercivities as high as 104 and 45 kOe at room temperature, respectively, were achieved by carefully controlling the nitrogenation process The coercivity strongly depends on the preparation route, ie, annealing temperature as well as nitrogenation temperature and time By the detailed investigation of the influence of these conditions, the optimum process parameters were determined The coercivity mechanism of melt-spun NdFe105Mo15Nx powders shows characteristics of a randomly oriented single domain particle system Poor coercivities have been obtained for Nd(Fe,V)12 and Pr(Fe,V)12 In these cases as well as for not optimally nitrogenated Nd(Fe,Mo)12, the low coercivity of the nitrided po

Hard magnetic properties of melt-spun R(Fe,M)12 nitrides (R=Nd or Pr; M=Mo or V)

The magnetocrystalline anisotropy of YFe12-xMox and YPe12-xMoxNy (x=1-3, y approximately=1) have been investigated by X-ray diffraction and the singular point detection technique. The uniaxial anisotropy of the YFe12-xMox series decreases with increasing Mox concentration with a clear turning point at about x=1.6. The anisotropy characteristic of the nitride YFe12-xMoxNy changes into a canted-type anisotropy for x or=1.5. The anisotropy reduction for YFe12-xMox is mainly due to the substitution of Mox atoms on the 8i sites, while the further change in anisotropy for YFe12-xMoxNy may be due to a change in the 3d orbital moment or to a change in crystal-field interaction by the interstitial Ny atoms.

Study of the magnetocrystalline anisotropy of YFe12-xMox and YFe12-xMoxNy (x=1-3, y approximately=1)

A series of iron‐rich ternary intermetallics PrFe12−xMox (x=0.5, 0.75, 1.0) and their nitrides have been prepared by arc melting, annealing at 1273–1393 K and water quenching. A single‐phase structure of the ThMn12 type has been obtained for x=1.0 when annealed at 1345 K (with α‐Fe<5%). The lattice constants are a=8.5978(2) A, c=4.7795(3) A. The alloys exhibit planar anisotropy, a Curie temperature of 498 K, and a room‐temperature magnetization of 120.4 A m2/kg prior to the nitrogenation. After nitrogenation the anisotropy changes to uniaxial, the Curie temperature increases to 681 K, and the room‐temperature magnetization becomes 136 A m2/kg. A lattice expansion corresponding to 2.4% of the cell volume is observed. In the x=0.5 and x=0.75 alloys, a secondary 2:17 phase is also present, besides the 1:12‐type structure. The peritectic decomposition temperature is 1393 K for all samples.

Synthesis and magnetic properties of PrFe12−xMox and PrFe12−xMoxNy (0.5≤x≤1.0, y≊1)

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.

Ming‐hou Zhang

Papers

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