[en] The microalloying effect of Cu and Nb on the microstructure and magnetic properties of an Fe₃B Nd₂Fe₁₄B nanocomposite permanent magnet has been studied by transmission electron microscopy (TEM) and atom probe field ion microscopy (APFIM). Additions of Cu are effective in refining the nanocomposite microstructure and the temperature range of the heat treatment to optimize the hard magnetic properties is significantly extended compared with that of the ternary alloy. Combined addition of Cu and Nb is further effective in reducing the grain size. Optimum magnetic properties obtained by annealing a melt-spun Nd_4.5Fe_75.8B_18.5Cu_0.2Nb₁ amorphous ribbon at 660 C for 6 min are B_r = 1.25 T, H_cJ = 273 kA/m and (BH)_max = 125 kJ/m³. The soft magnetic Fe₂₃B₆ phase coexists with the Fe₃B and Nd₂Fe₁₄B phases in the optimum microstructure of the Cu and Nb containing quinternary alloy. Three-dimensional atom probe (3DAP) results show that the finer microstructure is due to the formation of a high number density of Cu clusters prior to the crystallization reaction, which promote the nucleation of the Fe₃B phase. The Nb atoms appear to induce the formation of the Fe₂₃B₆ phase when the remaining amorphous phase is crystallized

[en] Developments in the field of high-energy Nd-Fe-B magnets are reviewed and discussed. The highest value of the maximum energy product (BH)_max reported so far for sintered Nd-Fe-B magnets is 416 kJ/m³ (52 MGOe), while a (BH)_max of 360 kJ/m³ (45 MGOe) has been realized in commercial production. The highest (BH)_max value obtained by means of rapid solidification and hot-pressing processes is around 380 kJ/m³ (48 MGOe). Rapidly solidified isotropic magnets with high squareness are also described

[en] Nanostructured Nd-Fe-B magnets prepared by crystallization of amorphous precursors have attracted considerable research interest due to the effect of remanence enhancement induced by the intergranular exchange interaction. Recently, additions of Cr were found to be very effective to improve hard magnetic characteristics of Nd_xFe_82-xB₁₈ (x = 3.5 to 5.5) nanocomposites. This improvement was due to the Cr-induced formation of Nd₂Fe₁₄B. However, despite its significance, little is known about the mechanism underlying this microstructural change induced by Cr. This preliminary study suggests that the effect of Cr on the crystallization kinetics of the precursor amorphous plays an important role in determining the phase constituent after crystallization. The aim of this paper is to report new results on the effect of Cr on the decomposition process of amorphous Nd₅Fe₇₄Cr₃B₁₈, with the specific goal of identifying the mechanism of the Cr-induced formation of Nd₂Fe₁₄B

[en] Effects of Ti and C additions on structural and magnetic properties of Fe_xB/Nd₂Fe₁₄B-type nanocomposite permanent magnets (x=3 or ((23)/(6))) prepared by means of rapid solidification and subsequent annealing in a B-rich and Nd-poor composition range are reported. Addition of Ti suppresses formation of primary Fe and promotes formation of ferromagnetic iron-borides. Carbon addition is effective for grain refinement and suppression of unfavorable formation of TiB₂, resulting in improvement of magnetic properties. Compositional adjustments have yielded a series of Fe_xB/Nd₂Fe₁₄B-type isotropic nanocomposite permanent magnets with magnetic performance comparable to near-single-phase isotropic melt-spun magnets in a composition range B>10 at% and Nd<10 at%

[en] Studies of anisotropy-coercivity correlation, microstructure and effects of surface conditions on coercivity, which have been undertaken at this laboratory in order to clarify the origin and mechanism of the intrinsic coercivity in sintered rare earth-iron-boron magnets, are reviewed. New results concerning the origin of the heat treatment effects are also disclosed

[en] High energy-products exceeding 430 kj/m³ (54 MGOe) have been realized on anisotropic permanent magnets based on the Nd₂Fe₁₄B phase, recently. To produce extremely high-energy-product permanent magnets, special processes have been designed in order to realize the minimum oxygen content, the maximum volume fraction of the hard magnetic Nd₂Fe₁₄B phase, the highest orientation of the easy axis of magnetization, and small and homogeneous crystalline grain sizes in the finished magnets. For the powder metallurgical process, special techniques such as low-oxygen fine powder processing and magnetic alignment using pulsed magnetic fields have been developed. It has been shown that a good control of both homogeneity of distribution of constituent phases and the narrowness of the size distribution in the starting powder have great influences on the magnetic energy products. It is emphasized that the recently developed techniques are applicable in a large-scale production, meaning that extremely high-energy-product magnets are available on commercial basis. (orig.)

[en] The large variation of the hyperfine fields (HFF) at Co nuclei in several series of rare earth-cobalt intermetallic compounds is interesting since it may be related partly to large anisotropy energies of these materials. In RCo₂ the Co atoms occupy the 3m sites with the three fold axis lying along one of the <111> directions. The Co sites are distinguishable by the angle 0 between the Co moment and the symmetry axis at that site. Two peaks with the intensity ratio of 3:1 should be observed in the spin echo spectra of ⁵⁹Co in the RCo₂ with the <111> easy axis, whereas one resonance is expected for the compound with the <100> easy axis. The observed spin echo spectra are shown. It was concluded that all spectra are due to ⁵⁹Co in magnetic domains or in domain walls from the observations of frequency-shifts and intensity-changes under applied magnetic fields up to 50kOe. Possible mechanisms to explain the large anisotropy in hyperfine fields are discussed. (UK)

[en] Magnetization distribution in Nd-Fe-B nanocomposite magnets was investigated by electron holography, using a new pole piece apparatus dedicated to observations of nanocrystalline ferromagnetic materials. The exchange coupling between the magnetically soft and hard grains of 20-30 nm was experimentally verified by this microscopic study with improved resolution

[en] After a short review on temperature dependence of the intrinsic coercivity in sintered Nd--Fe--B-type magnets is given, recent experimental results concerning the coercivity--anisotropy (H/sub c/-H/sub A/) correlation in B-rich Pr--Fe--B and Nd--Fe--B sintered magnets and the influence of the surface conditions of the sintered Nd--Fe--B magnets on the coercivity are reported. The results are interpreted in terms of the μ₀H/sub c/ vs cμ₀H/sub A/-NI/sub S/ plot, where I/sub S/ is the spontaneous magnetization of R₂Fe₁₄B (R = Pr or Nd) and N is the effective demagnetization field coefficient

[en] The state-of-the-art description of the magnetic hardening mechanism in the sintered Nd-Fe-B permanent magnet is given. Recent experimental results concerning the coercivity-anisotropy (H/sub c/-H/sub A/) correlation in B-rich Pr-Fe-B and Nd-Fe-B sintered magnets and the influence of the surface conditions of the sintered Nd-Fe-B magnets on the coercivity are reported. These results are interpreted in terms of the μ/sub O/H/sub c/ versus c μ/sub Q/H/sub A/-NI/sub S/ plot, where I/sub S/ is the spontaneous magnetization of R/sub 2/Fe/sub 14/B (R=Pr or Nd) and N the effective demagnetization field coefficient