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1.
We present an analysis of the magnetization process of NdFeB-type magnets which exhibit a constriction or a shoulder of the demagnetization curve near the remanence point Br. This constriction which drastically reduces the maximum energy product of the permanent magnet is discussed in terms of i) a siperposition of a soft and a hard magnetic phase, ii) an oxidation process of surface layers, iii) and the spin reorientation which changes the magnetic structure from easy c-axis to easy cone below 135 K. We demonstrate that the effect of surface oxidation and of a soft magnetic phase are of considerable influence over the entire temperature range while the influence of the spin reorientation is dominant below 150 K. The appearance of the cone structure prevents the application of NdFeB magnets in a magnetic circuit below 150 K.  相似文献   

2.
The effect of small additions (1 at%) of some elements (P, Cr, Ti, Zr, Pb or Sn) on the corrosion behaviour and magnetic properties of Nd15Fe77B8 sintered magnets has been investigated. It was established that most advantageous was the addition of 1 at% Cr which distinctly inhibited both acid and atmospheric corrosion processes while it did not deteriorate the magnetic characteristics of the magnet. Addition of Cr accelerates, however, the dissolution of the magnet at strongly cathodic polarization.  相似文献   

3.
The corrosion behaviour of uncoated bonded NdFeB magnets prepared using different binders has been assessed in a humid environment (100°C, saturated water vapour) by means of mass change measurements and magnetic characterisation. Epoxy resin, zinc and polytetrafluoroethylene (PTFE) have been used to bond melt spun ribbon, MQP-D, as supplied by General Motors. It has been found that the PTFE bonded samples which had been heat treated prior to testing exhibit superior corrosion resistance to the other samples, as characterised by a smaller mass change and greater retention of magnetic properties.  相似文献   

4.
Rapidly quenched NdFeB alloys were prepared with varying grain sizes well below and above the critical size for single domain particles. The contributions of the single and multi-domain particles to the initial magnetization curve are analyzed. By changing the quenching speed, i.e., the average grain size, the shape of the initial magnetization curve changes characteristically. The volume fraction of single domain grains is determined from the initial magnetization curves. From scanning electron micrographs the grain size distribution is evaluated and the critical size for single domain particles in the bulk material is deduced from a quantitative analysis of the magnetization curves. It reaches twice the value of the theoretical value for isolated spherical particles. A low temperature treatment following the thermal demagnetization lowers the initial susceptibility in underquenched ribbons as well as in an MQIII magnet. This effect reflects the irreversibility of the transition from the multi to the single domain particle state during the cooling. The temperature dependence of the single domain particle size is deduced from the initial magnetization curves of low temperature treated samples. It is shown that these experimental results are consistently explained assuming the nucleation mechanism to apply for rapidly quenched NdFeB magnets. The results are compared to the behaviour of hard ferrites.  相似文献   

5.
Kim  Eng Chan 《Hyperfine Interactions》2002,139(1-4):607-614
The addition of Co to Nd4Fe77.5–x Co x Hf0.5Ga0.5B18.5 (0x5) was found to enhance the magnetic properties of Fe3B/Nd2Fe14B nanocomposite magnets. The enhancement resulted from the fact that Co tends to retard the formation of Fe3B from the amorphous matrix but to accelerate that of Nd2Fe14B. The decreased interval between the crystallization temperature of Fe3B and Nd2Fe14B led to a uniform grain size distribution of both phases during the annealing treatment. The additive Co was confirmed to partition mainly to Nd2Fe14B crystals rather than to Fe3B which was traced by XRD and Mössbauer spectroscopy as well. About 72 vol.% of Fe3B, 27 vol.% of Nd2Fe14B, and a small amount of Fe around 1 vol.%, respectively, were found to form. However, the volume fraction of each phase did not vary by the addition of Co up to 5 at.%.  相似文献   

6.
7.
8.
《Physics letters. A》1987,123(1):31-33
We present the results of a study of the crystalline structure of the high-temperature superconducting (above 110K) phase in the single-phase ceramic compounds YBaCuO. We have concluded that the crystal symmetry of this HTS phase with chemical composition Y1.2Ba0.8CuO4−δ is orthorhombic type with crystallographic lattice constants a=0.3815 nm, b=0.3457 nm, c=2.650 nm.  相似文献   

9.
The electromagnetic wave-absorption properties of Nd3Fe68−xMnxCo18B11 (x=0, 1, 2) alloys obtained by rapid quenching from the melt was studied. The complex permittivity-frequency and permeability-frequency properties were determined in the microwave frequency regime of 2–18 GHz by vector network analysis. XRD spectra showed that only α-Fe diffraction peak was observed in the as-spun alloys. It is found that the acquired complex permittivity and permeability values match the microwave frequency when the 1 at% Mn content was doped. A minimum reflection loss of −6.9 dB is obtained at 2.7 GHz for composite Nd3Fe66Mn2Co18B11 with absorber thickness of 1.5 mm. The exchange interaction was attributed to the microwave absorption properties. The results suggest a new design of microwave absorbers based on electromagnetic wave-absorbing materials.  相似文献   

10.
The effect of Co on the thermal stability and impact toughness of sintered Nd–Fe–B magnets has been investigated. The results showed that the addition of Co decreased the intrinsic coercivity and the temperature coefficient of remanence (α), and increased the temperature coefficient of coercivity (β) for sintered Nd–Fe–B magnets. The impact toughness of sintered Nd–Fe–B magnets with the addition of Co first decreases, reaches a minimum, and then starts to increase. The possible reasons for increasing the temperature coefficients of coercivity (β) for sintered Nd–Fe–B magnets were analyzed, and the relations between the microstructure and impact toughness of sintered Nd–Fe–B magnets were studied.  相似文献   

11.
Microstructure and magnetic properties of melt-spun nanocomposite magnets with nominal compositions of (Nd1−xPrx)9Fe86B5 (x=0–1) were investigated. Substitution of Nd by Pr could significantly improve the hard magnetic properties of the nanocomposite magnets; the intrinsic coercivity (iHc) and the maximum magnetic energy product ((BH)max) increase from 414 kA/m and 124 kJ/m3 for x=0 to 493 kA/m and 152 kJ/m3 for x=0.6, respectively. Further substituting Nd by Pr (x>0.6) strongly weakens exchange-coupling interaction between magnetically hard and soft phases.  相似文献   

12.
We investigate the effect of the optimized aging processing on magnetism and mechanical property of the sintered Dydoped Nd–Fe–B permanent magnet. The experimental results show that the magnetism, especially intrinsic coercivity, of the optimized aged Dy-doped Nd–Fe–B magnet is more excellent than that of the sintered one, but the former's strength and hardness are lower than that of the latter. It was observed that the optimized aged Dy-doped Nd–Fe–B magnet have more uniform grain size, thinner(Nd, Dy)-rich boundary phase. By means of the EBSD technology, the number of larger angle grain boundaries in the optimized aged Dy-doped Nd–Fe–B magnet is more than that of the sintered one. The reasons for the increased intrinsic coercivity and decreased mechanical properties of the optimized aged Dy-doped Nd–Fe–B magnet are also discussed.  相似文献   

13.
We have determined the temperature dependence of the internal hyperfine field, isomer shift, and quadrupole shift at each of the six iron sites in Nd2Fe14B. The hyperfine parameters are consistent with the local iron site environments. The quadrupole and isomer shifts and their temperature dependences support our assignments of the relative ordering of the internal hyperfine fields as j2>k2>ck1>j1>c. We obtain a Mössbauer temperature of 390 K for Nd2Fe14B, which compares well with the Debye temperature of 420K for pure iron.  相似文献   

14.
《Solid State Ionics》1988,31(2):127-130
Amorphous products were obtained in the LiBSe ternary system by quenching melts of Li2Se, B and Se mixture prepared at 100°C in sealed silica tubes. The vitreous region was slightly lower selenium composition than that of the Li2SeB2Se3 tie-line. The amorphous products were lithium ionic conductors and most of them showed contributions to their total conductivity. The amorphous product of composition Li25B36Se39 has the least electronic contribution to its total conductivity of 6.0 × 10−6 S/cm at room temperature. A new crystalline compound and crystalline LiBH4 were also obtained in LiBSe ternary. Both of them were lithium ionic conductors having conductivities of about 1 × 10−6 S/cm at room temperature.  相似文献   

15.
The oxide compounds of Ba0.6Y0.4−xScxCu (x=0.05−0.35) have been prepared. It was found that the superconducting transition temperatures of the samples vary with the contents of Sc and when Sc>0.325, the samples become nonsuperconducting.  相似文献   

16.
Significant efforts have been put into the recycling of bulk Nd–Fe–B sintered magnet wastes around the world in the past decade because bulk Nd–Fe–B sintered magnet wastes are valuable secondary rare-earth resources.There are two major facts behind the efforts.First, the waste magnets contain total rare-earth content as high as more than 30 wt.%, which is higher than most natural rare-earth mines.Second, the waste magnets maintain the physical and chemical properties of the original magnets even with deterioration of the properties on surfaces due to corrosion and contamination.In this review,various techniques for recycling bulk Nd–Fe–B sintered magnet wastes, the overall properties of the recycled Nd–Fe–B sintered magnets, and the mass production of recycled magnets from the wastes are reviewed.  相似文献   

17.
Rapidly solidified (RS) Nd2Fe14B alloys were prepared by melt-spinning under different melt treatment conditions i.e., the melt temperature was varied prior to ejection onto the quenching wheel. X-ray diffraction, transmission electron microscopy, thermal analysis and magnetic measurement were conducted on the as-quenched alloys to investigate their structural and magnetic characteristics. RS Nd2Fe14B alloys may display a variety of microstructures depending upon the thermal history of the melt before ejection: it was possible to synthesize an entirely amorphous structure, a partially amorphous structure containing nuclei and/or nanophases and a nanocrystalline structure. The relationship between the formation of crystalline nuclei or nanophases and the thermal history of the melt was studied. A lower melt ejection temperature produced a nanocrystalline microstructure, while higher melt ejection temperatures (T>1723 K) largely eliminated the presence of nuclei and associated nanophases and produced an amorphous product. The experimental results indicated that optimization of the melt treatment conditions will produce rapidly solidified Nd–Fe–B alloys with a more uniform microstructure.  相似文献   

18.
The effects of oxidation of Dy H3 with respect to dysprosium addition to Nd–Fe–B sintered magnets are examined.Samples sintered with the addition of freshly milled dysprosium hydride, dysprosium hydride exposed to air at room temperature for 15 min and dysprosium hydride exposed to air at 100°C for 3.5 hours are studied from the aspects of magnetic properties, microstructures, and their degradation, respectively. It is found that some oxidized dysprosium is distributed in the Nd-rich phase; hence, the decrease of remanence occurred. The degradation results indicate that preoxidised dysprosium can be a major factor in increasing the corrosion rate. The microstructures and corrosion acceleration test suggested that the oxidation is detrimental to remanence.  相似文献   

19.
Based on X-ray diffraction and electron microscopy data on morphological inhomogeneities at the interfaces in Fe?B ribbons, the boundary boron concentration separating the crystal and amorphous states upon spinning (~10 at %) is established. A modulated isotropic stochastic wave structure is detected, the relaxation of which can be presented as spinodal decomposition.  相似文献   

20.
Mössbauer studies have been performed between 6 K and 300 K on single crystals of 57Fe-doped K0.30MoO3, which show a Peierls transition at 180 K towards on incommensurate charge density wave state. The spectra show three doublets. A strong line broadening below 120 K indicates that the Fe impurities are strong pinning centers for the charge density wave above ∼ 120 K and become progressively weak pinning ones below, in agreement with theoretical models.  相似文献   

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