J.B. Dunlop

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

A structural determination of the new magnetic ternary rare-earth iron-rich intermetallic Nd3(Fe1−xTix)29 phase, previously reported as Nd3(Fe1−xTix)19, has been carried out by means of powder X-ray diffraction on a Nd3(Fe0.955Ti0.045)29 sample. The structure is monoclinic with the space group P21c (No. 14). There are two Nd sites, namely 2a and 4e, and fifteen Fe(Ti) sites in the structure, one 2d and fourteen 4e sites. The refined lattice parameters are a=10.641(1) A, b=8.5913(8) A, c=9.748(1) A and β=9 (6)δ, and Z=2. The structure is a new intermediatestructure between the well-known rhombohedral Th2Zn17 and tetragonal ThMn12 structures. All these three structures are derived by the replacement of a fraction of the Ca(Th or Nd) atoms in the CaCu5 structure by a pair of Cu(Zn, Fe(Ti) or Mn) atoms (dumb-bells) along the c-axis of the CaCu5 structure. The relationship between these three structures will be discussed in terms of the dumbbell substitution sequence in the hexagonal CaCu5 structure. The fractions of dumbbell replacement are 13, 25 and 12 for the Th2Zn17, Nd3(Fe1−xTix)29 and ThMn12 structures, respectively. It has been shown that only light rare-earths and Gd form the new Nd3(Fe1−xTix)29 phase, while for heavy rare-earths beyond Tb there should exist another new structure type.

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

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.

Analysis and design optimisation of magnetic couplings using 3D finite element modelling

Accurate analysis and optimal design of magnetic couplings are essential to minimise the volume of magnet material and to avoid the construction and testing of multiple models to achieve a given design goal. This paper compares the results of using 3D and 2D finite element analysis (FEA) and analytical methods with experiment. It is found that 3D analysis provides superior agreement. Design of FEA meshes in 3D and 2D are discussed. A method of correcting 2D FEA for end leakage is presented. Optimisation using 3D FEA, combined with computer search techniques, is demonstrated.

Magnetic viscosity in NdFeB and SmCo5 alloys

Abstract The magnetic viscosity parameters ( kT/q = S v ) of spherical specimens of NdFeB and SmCo 5 have been measured as functions of intensity of magnetization. Two methods of measurement were used for both specimens. For the NdFeB specimen the value of kT/q varies from 50 Oe at M =+400 G to 80 Oe at M =-900 G. For SmCo 5 , kT/q varies from approximately 18 to 21 Oe and has a maximum value at M =0. For each specimen the two methods of measurement give results which are in agreement within the limits of experimental error. The volumes of material which are subject to thermal activation, e.g. pinning or nucleation centres, range from 4 to 6.4X10 -19 cm 3 for NdFeB and is about 2.4X10 -18 cm 3 for SmCo 5 .

Magnetic properties of interstitially modified Nd3(Fe,Ti)29Xy compounds (X=H, C, and N)

The effects of light atom intercalation on the magnetic properties of the monoclinic compound Nd3(Fe,Ti)29 have been studied by Mossbauer spectroscopy and thermogravimetric analysis. Maximum contents of 4 nitrogen atoms and 6 hydrogen atoms per formula unit have been achieved, consistent with structural calculations. The associated lattice expansion ranges from 2% in the hydride to 6.5% in the nitride. Attempts to introduce carbon were unsuccessful as the material decomposed rapidly during the reaction. Both hydrogen and nitrogen additions lead to substantial increases in the magnetic ordering temperature, but only the nitrogen leads to an increase in the iron moment.

Phase equilibria in the Fe‐rich corner of the Nd‐Fe‐Ti ternary alloy system at 1100 °C

High‐temperature phase relations in the Fe‐rich corner of the Nd‐Fe‐Ti ternary alloy system have been investigated and an equilibrium phase diagram has been constructed at 1100 °C. Arc‐melted and annealed alloys of systematically varying compositions were characterized utilizing scanning electron microscopy, an energy dispersive x‐ray microanalysis system (EDS), x‐ray diffraction, and optical metallography. Three major phases have been identified, the well known Nd(Fe,Ti)12 ‘‘1:12’’ (ThMn12‐type structure) and Nd2(Fe,Ti)17 ‘‘2:17’’ (Th2Zn17‐type structure) compounds, and a phase with approximate composition Nd2(Fe,Ti)19 ‘‘2:19.’’ The crystal structure of the latter phase has very recently been solved, and the ‘‘ideal’’ composition shown to be Nd3(Fe,Ti)29 ‘‘3:29.’’ Quantitative EDS data has been used to identify the compositional limits for the three major phases. Annealing the ‘‘1:12’’ and ‘‘3:29’’ ternary phases at 900 °C results in a slow decomposition into Nd2(Fe,Ti)17, Fe2Ti, and α‐Fe(Ti).

Magnetic properties of nanocomposite and materials with an excess of Fe

Two-phase nanocomposite materials have been prepared by high-energy ball-milling (HEBM) (2:14:1 phase) (u = 0, 0.75, 1.5 or 3.0; y = 0 or 11.6 and z = 0 or 0.5) or (1:12 phase), with excess Fe and then annealing. Magnetic properties of materials containing volume fractions of up to 75% of a magnetically soft Fe phase have been investigated and remanence enhancement observed. Optimum magnetic properties are obtained for materials with a volume fraction of a magnetically soft phase of 37 - 40%; for -Fe powders a remanent magnetic polarization of 1.05 T and intrinsic coercivity of ; and for -Fe powders a remanent magnetic polarization of 0.85 T and intrinsic coercivity of . For Co-containing alloys, evidence was observed for the redistribution of Co in the HEBM process, resulting in a magnetically soft Fe(Co) phase. The magnetic properties of isotropic -Fe and -Fe type magnets, compacted by hot pressing, are reported.

TWO-STAGE NANOSTRUCTURAL FORMATION PROCESS IN FE-NB-B SOFT MAGNETIC ALLOYS

The nanostructural formation kinetics in a soft magnetic Fe80Nb6B14 alloy have been investigated by means of differential scanning calorimetry, thermogravimetric analysis and transmission electron microscopy. Unlike nanocrystalline Fe–Zr–B soft magnetic alloys, where the nanocrystallite formation is governed mostly by a nucleation and growth mechanism, the nanostructural formation mechanism in the Fe–Nb–B alloy shows a change in the fraction transformed range 0.1–0.2. The first‐ and second‐stage nanostructural formation processes have been described by the nucleation and growth and grain‐growth models, respectively. This two‐stage nature in the nanostructural formation kinetics can be attributed to a high population density of the primary bcc nuclei.

Structural and magnetic properties of the novel compound Dy3(Fe,Ti)29

Microstructural characterisation, by means of energy dispersive X-ray microanalysis and X-ray diffraction of a Dy3Fe27.5Ti1.4 alloy annealed at 960°C for 7 days, has revealed the existence of a novel compound having the recently reported monoclinic Nd3(Fe,Ti)29-type structure. Thermogravimetric analysis (TGA) gives a magnetic ordering temperature of 438 K. Refinement of powder X-ray diffraction data by using the P21/c (a = 10.5759 A, b = 8.4962 A, c = 9.6704 A and β = 97.0472°) and A2/m (a = 10.5759 A, b = 8.4958 A, c = 9.6697 A and β = 97.0416°) space groups yields reliability R factors of 10.4% and 9.8% respectively. 57Fe Mossbauer spectroscopy measurements at room temperature yield an average 57Fe magnetic hyperfine field of 19.9(2) T, which corresponds to an average Fe magnetic moment of 1.3 μB.

57Fe Mössbauer measurements of the spin reorientation in Tm2Fe14B

57Fe Mossbauer spectra of Tm2Fe14B, measured above and below the spin reorientation temperature (∼310 K), have been analyzed and are entirely consistent with a rotation of the magnetization from the basal plane to the c axis as the temperature is increased.