Master ingots of binary Fe-Nd and ternary Fe-Nd-B alloys were prepared by arc melting under a highly puriﬁed Ar atmosphere using raw materials of 99.9% Fe, 99.9% Nd and Fe-18.9 mass%B mother alloy. Their chemical compositions are given in Table 1. Rapidly quenched ribbon was produced from the ingots by a single roller melt-spinning method at a roll surface velocity of 42 ms 1 in an Ar atmosphere. The
thalpy for the Fe-Nd alloy is too small to compensate the en- ergy gap between regular solution model and real solution of the present study. As shown in Fig. 7, the standard Gibbs en- ergies for the dissolution of oxygen into molten Ti-Al alloys are situated between the lines for dissolution energies for molten titanium and aluminum in proportion to molten Ti-Al composition. It means that oxygen atoms in molten Ti-Al al- loy are uniformly dispersed in the solution. However, the standard Gibbs energies for the dissolution of oxygen into molten Fe-Nd alloy are quite closer to that into molten Nd and very far from than that into molten Fe. It indicates that oxygen atoms in molten Fe-Nd alloy preferentially exist near neodymium atoms due to very strong affinity between oxy- gen and neodymium. Namely, the dissolution behavior of ox- ygen into molten Fe-Nd alloy is thermodynamically dominat- ed by chemical property of neodymium.
In Fig. 7, the calculated phase equilibria of the thermody- namic section at 870 K using the present thermodynamic parameters are in good agreement with the experimental data in the composition range of ³33100 at% Sb from Sologub and Salamakha. 40) Raghavan 49) reviewed this isothermal section and predicted 3 three-phase regions (e.g. bcc(Fe)+ FeSb +¸ 5 , bcc(Fe) +¸ 5 + NdSb and bcc(Fe) + Nd 4 Sb 3 + NdSb),
consequently, the Dy ion activity was increased in the bath. Moreover, the main constituent of the electrodeposit was Dy even after the Fe, Nd, and B were added to the bath in addi- tion to the Dy (Figs. 4 and 5). This is because Dy is more re- active to chlorination compared to the other elements. Thus, we conducted a thermodynamic examination in order to check whether Dy is more susceptible to chlorination relative to the other elements. Table 2 shows the change in the stan- dard Gibbs energy of formation for the chloride reaction at 1023 K (bath temperature) for each added metal. It shows that Dy and Nd have a greater negative change in their stan- dard free energy for the chloride formation than Fe and B. Therefore, we found that Dy and Nd were thermodynamical- ly more susceptible to chlorination during the evolution of chlorine at the anode by the electrolysis in the LiCl bath. The lack of Fe in the constituents of the electrodeposit is ascribed to the fact that it did not form a chloride. The fact that the electrodeposit consisted of only Dy, excluding Nd, seems to
and electron irradiation are indicated by solid circles and open squares, respectively. The composition ratio of the present metallic glass is indicated by the dotted line. Stability of crystalline phase may decrease with increasing unit volume under electron irradiation because thermal recovery by atomic diﬀusion becomes diﬃcult. With larger deviation of the composition ratio of a crystalline phase from the dotted line, more frequent redistribution of solute atoms is required to form the crystalline phase resulting in greater diﬃculty of crystallization from the viewpoint of kinetics in phase transformation. In fact, crystalline phases whose composi- tions show no large deviation from the dotted line preferen- tially appear during thermal annealing and electron irradi- ation. However, phase selection for electron irradiation induced crystallization is inﬂuenced by not only the phase stability but also kinetics of crystallization under electron irradiation. In electron irradiation induced crystallization, crystalline phases which have higher Fe composition than the dotted line were selected. This may be due to the diﬀerence in electron knock-on eﬀect among Fe, Nd and B atoms. Since the atomic radius of Nd is the biggest among these three elements, dynamic displacement of Nd by elastic collision of electrons occurs more frequently than that of Fe and B atoms
compound did not maintain its original structure under electron irradiation and was transformed to an amorphous phase through solid-state amorphization. With further electron irradiation, crystallization of the amorphous phase occurred forming a nano-crystalline structure. The phase selection of electron irradiation induced crystallization depended strongly on the irradiation temperature; nanocrystalline -Fe phase precipitated in the amorphous phase at 104 K, while a nanoduplex structure composed of -Fe, compounds and residual amorphous phase was formed at 298 K. Electron irradiation induced phase transformation is a very eﬀective method to control the nanocrystalline structure in Fe-Nd-B alloy. [doi:10.2320/matertrans.47.1762]
Metal hexacyanoferrates (MHCFs), such as the Prussian blue and its analogues (PBAs), have previously been exploited as battery electrode materials in secondary cells; however, their applications as the anodic catalyst of fuel cells are sparsely reported in the literatures [36-39]. Fortunately, as promising catalytic materials for aliphatic alcohol electrooxidation, their specific electrocatalytic activity when decorated on the glass carbon electrodes in ruthenium-iron cyano-bridged complex patterns has been recognized to a certain extent . In the past few decades, a series of Ln-Fe cyano- bridged 3d-4f complexes, with or without an organic ligand in their molecular structure, have been extensively developed mainly due to their extraordinary molecular magnetic character rather than their catalytic activity [41-44], while a platinum electrode decorated with the hybrid-metallic cyano-bridged d-f complexes exhibit excellent electrocatalytic activity towards the electrooxidation of methanol and formic acid in our previous works [45-46].
The enhancement of the uniaxial anisotropy of Nd is at- tributed to the Fe substitution with Cu; the interaction be- tween Fe 3d electrons and Nd 5d electrons becomes weaker. As a result, the distribution of 5d electrons becomes more in the z direction. When the 5d electrons are distributed in the z direction, the 4f electrons with large orbital angular momen- tum are distributed within the (001) plane, thereby strength- ening the uniaxial anisotropy of Nd. Figure 6 shows the re- gion with increased electron density by the Cu substitution for the bulk single crystal, where one Fe atom at the 4c site in the Nd-Fe-B plane is substituted with Cu. This figure does not include the 4f electron distribution. The electron density surrounding the Cu atom is reduced, indicating the fact that the interaction between the 3d electrons and 5d electrons is weakened. Furthermore, we can see that the electron density near the Nd site is elongated in the z direction, and the uni- axial anisotropy of Nd is enhanced as described above.
Figure 3 shows the XRD patterns of these as-sintered compacts together with pattern of the glassypowder for comparison. The diﬀraction patterns of the samples sintered at the conditions of 763 K-60 s, 788 K-60 s and 788 K-420 s consist of a halo pattern, and no detectable diﬀraction peak of crystalline phase is seen, in agreement with the original glassypowder. However, the increase in the sintering time to 900 s at 788 K results in additional appearance of crystalline peaks which are identiﬁed as Fe 3 B phase. The diﬀraction
A total of 21 compositions was prepared in this system with results listed in Supplementary Table 3. All compositions were given a final heat treatment at 950 °C for 12 h in air. From these results, the ternary phase diagram, Fig. 3, was constructed. Powder XRD highlighted two new findings of note: first, as well as phase Y, a limited series of phase Y solid solution of general formula Li 11-x Nd 18 Co 4 O 39- formed over the
The microstructures were observed by ﬁeld emission scanning electron microscopy (FESEM) and analyzed by electron backscatter diffraction (EBSD). The plane of magnets parallel to the magnetically aligned direction were polished using SiC abrasive paper down to #4000 and a colloidal silicate suspension. The microstructure was eval- uated using a grain analysis image created by combining the backscattered electron image (BEI) and EBSD images (Fig. 1). The grain boundary between the Nd 2 Fe 14 B grain and
alloy was cooled to room temperature, and the DR treatment was performed. The HDDR alloy was subjected to hydrogen decrepitation for 5 h at 200°C under a hydrogen atmosphere, and then pulverized to a powder by He jet milling. For comparison, the original SC alloy was also pulverized by hydrogen decrepitation and He jet milling. Here, jet-milled powders from the HDDR alloy and SC alloy are referred to as “jet-milled HDDR alloy powder” and “jet-milled SC alloy powder”, respectively. The jet-milled HDDR and SC alloy powders were annealed from 100 to 1000°C for 30 min under high vacuum (10 ¹4 Pa), and were quenched to room temper- ature. The magnetic properties of the powders were measured by a vibrating sample magnetometer (VSM). The powders were aligned with a magnetic ﬁeld of 2.0 T and ﬁxed with parafﬁn wax, and then magnetized in a pulsed magnetic ﬁeld of 8.0 T before VSM measurements. The composition of the powders was determined by X-ray ﬂuorescence (XRF) analysis. The microstructure was observed by ﬁeld-emission scanning electron microscopy (FE-SEM). The average particle size and particle size distribution are deﬁned as the median diameter (D 50 ) and relative span (RS), respectively.
A large number of experimental studies are devoted to measuring the thermophysical properties of substances in a magnetic field. It is known that under its influence curious thermal effects are observed in the magnetic materials. In particular there are magnetostrictive and magnetocaloric effects. The aim of the present work was to measure the linear thermal expansion coefficient (LTEC) of some technically important compounds of Nd-Fe-B and Sm-Co systems, as well as to clarify the question about the influence of the residual magnetization by density and thermal expansion of the samples. The materials which are used to create advanced permanent magnets with record values of the maximum magnetic product were investigated. Literature search revealed that the magnetic and structural properties of compounds with neodymium and samarium were studied in sufficient detail, which is impossible to tell of their thermal characteristics [1–5]. The results presented in this paper allow to partially fill the gap.
one of the most commonly preparation methods. The size, shape, and structural properties of electrodeposited nano- cylinders are controlled by the template and electrodepo- sition parameters. Well known to all, the permanent magnet materials consist of ferromagnetic materials and a rare earth metal. Inspired by these, ferromagnetic nano- wires doped with a rare earth element prepared and can change the magnetic properties of composites . To the best of our knowledge, Nd-doped magnetic nanocables have rarely been reported. We have prepared a series of rare earth-doped multilayer nanocable arrays and investi- gated their magnetic properties .
common interpretation is based on the nucleation of reverse domains. According to this theory, the morphologies of the complementary phases and magnetic domain structures are important, because such phases become the nucleation sites of reverse domains or inhibiters of domain-wall propagation. The details of such behaviours and functions, therefore, should be understood more clearly to achieve a breakthrough in developing higher-coercivity magnets. In particular, if the relationship between those microstructures and domain structures is clariﬁed, the guiding principle of microstructure control for higher-coercivity magnets will be suggested. Magnetic domain observation is one of the eﬀective approaches to reveal such mechanisms of magnetic reversal in the submicron scale. In fact, there have been a variety of domain observations and analyses reported for Nd-Fe-B magnets. 21) For instance, an optical microscope utilizing the Kerr eﬀect is the most prevalent method, 22–25) and is still
With increasing field, a metamagnetic transition near 6 T to full parallel alignment is found. When the field is de- creased a very large hysteresis is present. To confirm that the hysteresis is intrinsic to the compound and not due to the large sweep rate in the high-field experiments, we also mea- sured the magnetization in a SQUID magnetometer. When the maximum field is below the metamagnetic transition, as is the case in our SQUID measurements and the vibrating sample magnetometer ~ VSM ! measurements of Hu et al., 9 there will be no hysteresis in decreasing field. However, when the sample is cooled from room temperature to 5 K in a magnetic field of 5 T, the magnetic data agree perfectly with the high-field measurement in decreasing field. This is because the transition field for ferromagnetic alignment is zero at the ordering temperature ~ 230 K ! and the sample cooled in a magnetic field of 5 T is therefore already satu- rated. From these measurements it can be concluded that the Fe moments are ordered in at least two antiferromagnetically coupled sublattices and that the hysteresis is also due to the Fe-sublattice anisotropy. In Sec. IV, we will show that the FIG. 4. Temperature dependence of the magnetization of the
In addition, the morphology of the grain boundaries is an important factor that also requires careful investigation. For example, the roughness of the grain boundaries, which can be controlled by post-sintering heat treatment, can aﬀect nucleation of reverse magnetic domains. However, despite intensive study, the underlying mechanism for the improve- ment in the coercivity is still under debate. Transmission electron microscopy (TEM) is useful for gaining a deeper understanding of the eﬀect of post-sintering heat treatment on the coercivity, since it allows both the magnetic and crystallographic microstructures in Nd–Fe–B magnets to be observed. This is the motivation behind this study.