The bulk magnetic properties of (ErxY1-x)2Fe14B and (ErxPr1-x)2Fe14B systems were studied over the temperature range 4.2-1100 K. Lattice parameters, saturation magnetizations, Curie temperatures and spin reorientation temperatures were determined. Theoretical description of the detailed magnetic behavior is presented, based on a crystal field model. The (ErxY1-x)2Fe14B compounds were all found to exhibit plane-to-axis spin reorientations similar to that observed for Er2Fe14B, with the transition temperature decreasing with increasing Y content. In contrast, the spin reorientations in the (ErxPr1-x)2Fe14B systems appear to be of the cone-to-axis type. Since higher order crystal field terms appear to be significant only in the cases of Nd3+ and Ho3+, the results are discussed in terms of a crystal field Hamiltonian involving only 2nd order terms. Using known values of the exchange field, Fe anisotropy and the ratios of the crystal field coefficients, the multi-ion cr 6.tal field problem was formulated in terms of a single adjustable parameter (B02(f). It is shown that 2nd order crystal field terms are capable, not only of explaining the conical anisotropy of the (ErxPr1-x)2Fe14B systems, but also the decrease in the Er moment upon passing through the spin reorientation (as has been observed for Er2Fe14B). The magnetic structure of Er1.5Pr0.5Fe14B is also predicted.

Alloys of composition RCo7−xZrx (R=Pr or Er and x=0−0.8) were synthesized and characterized in the temperature range of 10–1273 K in fields up to 5 T. As with the SmCo7−xZrx system studied earlier in our laboratory, the effects of Zr doping on the stability of the TbCu7 phase and the increase in the anisotropy field HA are also observed in the systems of PrCo7−xZrx and ErCo7−xZrx. Nearly single phase TbCu7 materials were formed in as-cast alloys when x=0.1–0.2. In the case of R=Pr, HA changes from almost planar for x=0 to uniaxial with Ha∼100 kOe for x⩾0.2 at room temperature (RT). In the case of R=Er, HA for the x=0.1 composition is almost two times larger than that of the Zr-free alloys, which shows strong uniaxial anisotropy at both RT and 10 K. Spin reorientation behavior (when R=Pr) and R–M antiparallel coupling (when R=Er) were also observed.

Quaternary R1-xR'xFe14-xCoxB of mixed rare earth (where R = Nd, and R' = Tb or R = Tm and R' = Dy) intermetallics crystallize in tetragonal form isostructural to Nd2Fe14B alloy. Measurements of lattice parameter, saturation magnetization, Ms, magnetic ordering temperatures, T-C, spin reorientation temperatures, T-SR, and anisotropy fields, H-A, were determined. In Tm1-xDyxFe14B, Tm and Dy are rare earth ions characterized by second order Steven's coefficients with opposite signs. Progressive replacement of Tm by Dy enhances the anisotropy field H-A markedly. This was evidenced from the expansion of the uniaxial anisotropy temperature range determined by constructing the magnetic phase diagram. In NdTbFe14-xCoxB the anisotropy field is increased by almost two folds upon 50% substitution of Tb for Nd at room temperature. This behavior is ascribed to the stronger magnetic anisotropy of Tb ion in the lattice. The latter feature is crucial, in part, in improving the coercive force of NdFeB-based permanent magnets. The partial replacement of Co for Fe in the lattice also improves the magnetic ordering temperature, but reduces the saturation magnetization. Results are discussed in terms of the competing anisotropies of the 4f of the rare earth and 3d transition metal ions.

A brief review is presented of recent work dealing with the structure and magnetic properties of RCo 7−x Zr x alloys (R=Sm, Pr, Er, Gd, and Y). The experimental results obtained are consistent with a model in which Zr atoms partly replace dumbbell Co atoms and play an important role in stabilizing the TbCu 7 structure while significantly increasing the anisotropy field (HA). For example, when R=Sm, H A increases from 90 kOe for x=O to 130 kOe for x=0.2 at 300 K, and from 140 kOe for x=0 to 220 kOe for x=0.2 at 10 K. In the case of R=Y and Gd, HA is mainly contributed by the Co sublattice. For R=Y alloys, H A increases from 18 kOe for x=0 to 74 kOe for x=0.2 at 300 K and from 20 kOe for x=0 to 82 kOe for x=0.2 at 10 K. For R=Gd alloys, HA shows the largest enhancement. It increases from 35 kOe for x=0 to 140 kOe for x=0.2 at 300 K and from planar for x=0 to uniaxial with 182 kOe for x=0.2 at 10 K. In general, experimental results are in accord with the theory of Greedan and Rao for anisotropies of R-Co alloys. The magnetic moments for cobalt and rare earth in RCo 7−x r x compounds (x=0∼A).2) have been estimated from the experimental values. The results show that they are nearly the same as those in RCo 5 or R 2 Co1 7 . The Co moment is 1.5∼;1.6 μB. Some phase transition phenomenon between RCo 5 , RCo 7 , R 2 Co 17 and R 2 Co 7 at different heat treatment conditions will also be discussed.

The alloys with composition of SmCo7−xZrx(x=0–0.8) were synthesized and characterized in the temperature range of 10–1273 K and at fields up to 5 T. The experimental results show that a small amount of Zr substitution can contribute to a stabilization of the TbCu7 structure, and improve magneto-anisotropy Ha from 90 kOe for x=0–180 kOe for x=0.5 at room temperature, and from 140 kOe for x=0–300 kOe for x=0.5 at 10 K. It is probable that Zr may partly replace a dumbbell of Co atom pair in these alloys. The phase transition between CaCu5, TbCu7, Th2Zn17, and Ce2Ni7 at different heat treatment conditions was also discussed.

LaCo 13 and La(Co, Fe)13 alloys have been prepared and studied as high temperature, high performance soft magnetic materials. The dc magnetic properties have been measured over a temperature range of 10–1273 K in fields of 0 to 5 T. Data obtained show that the dc magnetic properties (Hc,K1) of the La(Co, Fe)13 bulk alloys are comparable with Fe bulk alloy and Tc=1021–1297 K are higher than that of Fe and Hiperco; ac magnetic properties are first time reported in a bulk LaCo13 alloy, showing a reasonably higher power loss than that of commercial Hiperco alloy. The ac magnetic properties can be improved by making LaCo13 alloys as laminated thin sheets.

Studies of the magnetic and structural characteristics of RCo9+δSi4 (δ=0–4), nonstoichiometric alloys, have been extended from R=La in our earlier work to R=Pr and Gd. In the present work, as the extra Co content increases, the magnetic properties M, Tc, and Hc are significantly enhanced compared to that of the stoichiometric alloys (δ=0). Using x-ray diffraction measurements, the sublattice occupancies are calculated. The extra Co atoms are found to occupy the 4a and 16L2 sites in the Ce2Ni17Si9 unit cell. They partially replace R and Si in these sites.

A nuclear-magnetic-resonance study of Fe16N2, Fe4N, and bcc alpha-Fe phases, along with magnetization experiments on samples containing these phases, show that the average Fe moment for Fe16N2 is between 2.7 mu(B) and 2.9 mu(B). This is in contrast to previous studies which report values ranging from 2.3 mu(B) to 3.5 mu(B). The results reported here indicate an average Fe moment for Fe16N2 which is significantly enhanced compared with that for alpha-Fe, and a moment for Fe atoms at the 4d sites which is greater than 3.0 mu(B).

The magnetism of LaCo13-type alloys such as LaCo13, PrCo13−xSix, etc., has recently received considerable attention as potentially useful magnetic materials. The present study is concerned with RCo13−xSix where R=La, Pr, Nd, Gd or Dy.

LaCo9+δSi4 and LaCo8.5+δSi4.5 alloys with δ=0 to 4 have been synthesized and characterized. The stoichiometric alloys (δ=0) have low Tc and small moments, whereas the alloys with δ≠0 have larger Tc and magnetization.

PrCo13−xSix alloys with 0 ≤ x ≤ 4.5 have been synthesized and studied at temperatures from 1 0 to 1273 K and in fields up to 17 kOe. The structure and magnetic properties of the alloys vary significantly with changes in Si content x. In the alloys with x = 0, TMA and XRD studies show the phases present to be Pr2Co17 and Co. For x = 1.5 or 2.0, the alloys are essentially single-phase fcc materials (NaZn13 structure type). At larger values of x the ternary alloy formed in a bct structure (Ce2Ni17Si9 structure type). Replacement of Co by Si in PrCo13 results in a drop in TC from 1318 K (for LaCo13) to ∼ 900 K for fcc Pr(Co,Si)13 alloy and to ∼ 20 K for bct Pr(Co,Si)13 alloys. There is also a large drop in magnetization from 104.6 emu/g for the alloy with x = 1.5 to 19.2 emu/g for the alloys with x = 4.0. A bct alloy (x = 3.5) showed negligible magnetic anisotropy. Si doping sharply reduces the Co moment. Si doping also reduces the Pr moment to 1.5μB (fcc alloys) and to 1.8μB (bct alloys). Nitrogenation fails to improve Pr(Co,Si)13 alloys as permanent magnet materials.

A series of TiMn multicomponent alloys based on the composition TiMn2 with high hydrogen storage capacity were investigated. It is found that the alloy Ti0.8Zr0.3Mn1.4Mo0.1V0.2Cr0.2 has a maximum hydrogen capacity of 3.4 H/M (mol H/mol alloy), theoretical electrochemical capacity of 560 mAh g−1, exhibits a plateau pressure range between 0.006 and 0.01 MPa at 293 K. Addition of the elements Si and Al in a four component alloy causes the hydrogen storage capacity to decrease and plateau pressure to increase. Addition of a small amount of Mo increases hydrogen storage capacity. The substitution of V for Mn lowers the plateau pressure dramatically. The phase composition and microstructure of Ti0.8Zr0.3Mn1.4Mo0.1 V0.2Cr0.2, which is one of the highest capacity TiMn2-based alloys, has been studied by X-ray diffraction, optical microscopy and scanning electron microscopy.

The magnetic properties of SmCo (2:17-type) magnets with high contents of Fe (v=Fe/3d≳0.34) and/or light rare earths (up to 0.4) were investigated. For magnets with compositions of Sm(FevCobalZr0.02Cu0.06{Ga}x)7.72, v=0.35, x=0–0.06, both iHc and (BH)max can be improved significantly by Ga doping, from 1.0 kOe and 5.4 MG Oe for x=0 to 6.4 kOe and 15.4 MG Oe for x=0.06. For magnets with compositions of Sm0.8Pr0.2(FevCobalZr0.02Cu0.06)7.67, v=0.30–0.31, iHc can be increased strikingly by a special heat treatment, from 2.5 to over 20 kOe for v=0.30 and from 0.5 to 15.5 kOe for v=0.31. Examining magnets with compositions of Sm0.59Pr0.41(Co0.68Fe0.20Cu0.10Zr0.02)z (z=6.68–7.75) shows two stages of the magnetization reversal process in the range of 5.5 to 9.5 kOe and 16 to 19 kOe. Observed (BH)max ranged from 17 to 22.5 MG Oe.

The α′-FeN phase was prepared by treating Fe powder with NH3H2 gas mixtures at a temperature of ≈ 665°C followed by a quench to cryogenic temperatures. Conversion of α to α′ to an extent exceeding 85% has been achieved. α″-FeN is produced by treatment of α′ for ≈ 1 to 2 h at 120–150°C. Bsat values obtained for α′- and α″-FeN are 23.5 and 26.6 kG, respectively. The latter corresponds to 2.9μBFe atom, a 34% enhancement over that of α-Fe.