Effects of Nb and C additions on the crystallization behavior, microstructure and magnetic properties of B-rich nanocrystalline Nd–Fe–B ribbons

The effects of Nb and C additions on the crystallization behavior, microstructure and magnetic properties of B-rich Nd_9.4Fe_79.6−xNb_xB_11−yC_y (x = 0, 2, and 4; y = 0, 0.5, and 1.5) alloy ribbons have been investigated. The results show that Nb and C additions change the crystallization behavior of Nd_9.4Fe_79.6B₁₁, avoid the formation of metastable Nd₂Fe₂₃B₃ phase, leading to the simultaneously precipitation of α-Fe and Nd₂Fe₁₄B phases. The results also show that Nb and C additions suppress the formation and growth of the soft α-Fe phases, leading to the presence of a large amount of Nd₂Fe₁₄B phases. Nb and C additions also refine the structure, and thus increase the exchange coupling interaction between the soft and hard phases. Excellent magnetic properties of B_r = 0.85 T, _iH_c = 1106 kA/m, and (BH)_max = 117 kJ/m³ have been achieved in Nd_9.4Fe_75.6Nb₄B_10.5C_0.5 alloy ribbons.     

Magnetic properties of low Mn-doped NiCuZn nanocrystalline ferrites

Low Mn-doped NiCuZn ferrites with compositions of (Ni_0.6Zn_0.3Cu_0.1)_1−xMn_xFe₂O₄ (where x = 0, 0.01, 0.02 and 0.03) were synthesized directly with sol–gel method. The influence of the Mn²⁺ content (parameter x) and the sintered temperature on the microstructure and the magnetic properties of these ferrites were mainly discussed. With the increasing Mn²⁺ content, saturation magnetization (M_s) of the powder samples decreased. Saturation magnetic flux density (B_s) and remnant magnetic flux density (B_r) of the toroidal specimens decreased with the Mn²⁺ content up to x = 0.02, followed by increasing. B_r and B_s both increased with the increasing sintered temperature, while coercivity (H_c) decreased. The real part of permeability (μ′) of the toroidal specimens increased up to x = 0.01, followed by decreasing. The sintered temperature also affected the resonance frequency and the useable frequency (from which the value of tan δ increased more) obviously. Furthermore, the low-frequency permeability and the secondary maximum (the maximum of the permeability appearing the secondary time) both increased with the sintered temperature from 70 to 120 and 150 to about 600.     

Ce、Y和Gd对Mg-3Sn-2Sr镁合金铸态组织和力学性能的影响(英文)

通过扫描电镜、X射线衍射、差热分析以及抗拉和蠕变性能测试等手段,调查和比较了Ce、Y和Gd对Mg-3Sn-2Sr镁合金铸态组织和力学性能的影响。结果表明:Mg-3Sn-2Sr三元合金主要由?-Mg、初生和共晶SrMgSn以及Mg2Sn相组成。当添加1.0%Ce、1.0%Y和1.0%Gd到Mg-3Sn-2Sr合金后,合金中分别形成了Mg12Ce、YMgSn、GdMgSn和/或Mg17Sr2相。同时,合金中初生SrMgSn相的形成被抑制,且呈针状的粗大初生SrMgSn相也被变质和细化。此外,添加1.0%Ce、1.0%Y和1.0%Gd均能同时改善Mg-3Sn-2Sr合金的抗拉性能和蠕变性能。在含Ce、Y和Gd合金中,含Ce合金的抗拉性能相对较含Y和含Gd合金的高。     

Tailored magnetic properties of Sm(Zn) substituted nanocrystalline barium hexaferrites

Sm and SmZn substituted nanocrystalline barium hexaferrites (Ba_1−xSm_xFe₁₂O₁₉ and Ba_1−xSm_xFe_12−xZn_xO₁₉, x = 0–0.6) were prepared by the sol–gel autocombustion process. X-ray diffraction (XRD) and vibrating sample magnetometer (VSM) were used to characterize the phase composition, crystal structure and magnetic properties of the as-prepared barium hexaferrites. All results indicated that the substitution content (x) critically influenced on the phase composition and magnetic properties. When the substitution content x > 0.2, impurity phases such as α-Fe₂O₃, SmFeO₃ and ZnFe₂O₄ were detected, which diluted and weakened saturation magnetization (M_s). For the Sm-doped samples, owing to the hyperfine field, canting spin, magnetic dilution and impurity phases, M_s increased with x firstly, and then decreased when x > 0.03. On the other hand, the coercivity (Hc) continuously increased with x. Nevertheless, for the SmZn-doped samples, M_s reached maximum when x = 0.06 and Hc almost unchanged with x. Compared the magnetic properties of Sm- and SmZn-doped samples, it was proved that Zn²⁺ substituted Fe³⁺ at 4f₂ sites and Sm³⁺ substituted Ba²⁺, which changed Fe³⁺ to Fe²⁺ at 2a sites in order to satisfy the electroneutrality principle.     

Comparative study of one-dimensional NiCo alloy nanostructures assembled by in situ and ex situ applied magnetic fields

For the study of magnetic field-assisted assembly behavior, one-dimensional (1D) NiCo alloy nanostructures were solvothermally obtained at 180 °C under an in situ magnetic field (the magnetic field as applied during the chemical reduction) and ex situ field (after the chemical reduction was finished). Microscopic morphology and magnetic properties differences were investigated using scanning electronic microscope (SEM) and vibrating sample magnetometer (VSM) for these products. Magnetic measurement results show that 1D ordered microstructures under in situ magnetic field possess higher saturation magnetization M_s, remnant magnetization M_r, coercivity H_c and reduced magnetization M_r/M_s than 1D ordered microstructures under ex situ field, and the four magnetic parameters of the two ordered microstructures are much higher than those randomly distributed alloy particles prepared in the absence of external magnetic field.     

Phase formation in rapidly solidified R2T17 intermetallics

Rapid solidification was utilized to produce a series of light and heavy rare earth-transition metal intermetallics in the R_H–Co, R_L–Co/Fe, and Sm–Co(Fe) systems with R_H = Dy and Tb and R_L = Pr and Sm. The influence of Nb–C and Zr–C additions on phase formation in the binary and ternary alloys has also been investigated. The X-ray diffraction patterns obtained with synchrotron radiation were refined by the Rietveld method for structural phase determination and analysis. It was found that the ability to create disorder strongly depended on the rare earth element, with light rare earth systems possessing more disorder, and rapid solidification effectively suppressed the development of long-range order in these compounds. Cobalt in contrast to iron favored the formation of disordered structures. Replacement up to two out of the three of the cobalt atoms with iron in the Sm–Co–Fe system has retained the establishment of the disordered TbCu₇-variant and exhibited complete cobalt–iron solubility. Additions of Nb–C and Zr–C have also greatly influenced the order formation. The comparison of lattice parameters of the intermetallic compounds obtained by rapid solidification to the parameters of equilibrium 2–17 phases summarized in the literature revealed that formation of partially ordered and disordered structures was associated with expansion of the both a- and c-axes in Th₂Zn₁₇- and Th₂Ni₁₇-type phases for all binary compounds.     

Synthesis,morphology, microstructure and magnetic properties of hematite submicron particles

We report on hydrothermal synthesis, plate-like morphology, microstructure and magnetic properties of hematite (α-Fe₂O₃) plate-like particles. The sample is obtained immediately after the hydrothermal process without using any template and without further heat treatment. The so-obtained sample is characterized by X-ray powder diffraction (XRPD), energy-dispersive X-ray spectroscopy (EDX), field-emission scanning electron microscope (FE-SEM), transmission electron microscopy (TEM), high-resolution TEM (HRTEM), and superconducting quantum interference device (SQUID) magnetometer. XRPD confirms the formation of a single-phase hematite sample whereas EDX reveals that iron and oxygen are the only components of the sample. SEM, FE-SEM, TEM and HRTEM show that the sample is composed of plate-like particles. The width of the particles is ～500 nm whereas thickness is ～100 nm (aspect ratio 5:1). The HRTEM images exhibit well defined lattice fringes of α-Fe₂O₃ particles that confirm their high crystallinity. Moreover, the HRTEM analysis indicates the plate-like particles preferring crystal growth along [0 1 2] direction. Magnetic measurements display significant hysteretic behavior at room temperature with coercivity H_C = 1140 Oe, remanent magnetization M_r = 0.125 emu/g and saturation magnetization M_S = 2.15 emu/g as well as the Morin transition at T_M ～ 250 K. The magnetic properties are discussed with respect to morphology and microstructure of the particles. The results and comparison with urchin-like, rods, spherical, hexagonal, star-like, dendrites, platelets, irregular, nanoplatelets, nanocolumns and nanospheres hematites reveal that the plate-like particles possess good magnetic properties. One may conjecture that the shape anisotropy plays an important role in the magnetic properties of the sample.     

Preparation and Magnetic Properties of MnFe2O4 Octahedral Microcrystals

MnFe₂O₄ octahedra have been prepared by reaction of Mn²⁺ ions and Fe³⁺ in alkaline condition via heat treatment of the coprecipitation product. The as-prepared powders were characterized in detail by conventional techniques such as powder x-ray diffraction; field emission electron microscopy and transmission electron microscopy. Vibrating sample magnetometer was used to determine the magnetic properties at room temperature. The results show that the MnFe₂O₄ octahedra were single crystals with cubic jacobsite structure and a size distribution from 0.8 to 1.0 μm. The octahedra obtained at 1100 and 1200 °C exhibited a ferromagnetic behavior with the coercive force (H _c) value of 49.03 and 39.23 Oe, saturation magnetization (M _s) value of 42.93 and 47.98 emu/g and remanent magnetization (M _r) value of 2.16 and 2.55 emu/g, respectively. It is indicated that the heat treatment temperature has a significant effect on the formation of the jacobsite structure. Furthermore, a possible mechanism was also proposed to account for the growth of these products.     

Low temperature sintering and properties of CaO–B2O3–SiO2 system glass ceramics for LTCC applications

The P₂O₅ + ZnO, ZrO₂ + TiO₂, B₂O₃ and a low-melting-point CaO–B₂O₃–SiO₂ glass (LG) are selected as the sintering additives, and the effect of their additions on the microwave dielectric properties, mechanical properties and microstructures of CaO–B₂O₃–SiO₂ system glass ceramics is investigated. It is found that the sintering temperature of pure CBS glass is higher than 950 °C and the sintering range is about 10 °C. With the above additions, the glass ceramics can be sintered between 820 °C and 900 °C. The dielectric properties of the samples are dependent on the additions, densification and microstructures of sintered bodies. The major phases of this material are CaSiO₃, CaB₂O₄ and SiO₂. With 10 wt% B₂O₃ and LG glass additions, the CBS glass ceramics have better mechanical properties, but worse dielectric properties. The _r values of 6.51 and 7.07, the tan δ values of 0.0029 and 0.0019 at 10 GHz, are obtained for the CBS glass ceramics sintered at 860 °C with 2 wt% P₂O₅ + 2 wt% ZnO and 2 wt% ZrO₂ + 2 wt% TiO₂ additions, respectively. This material is suitable to be used as the LTCC material for the application in wireless communications.     

Phase stability and electronic structures of YbAl3−xMx (M = Mg, Cu, Zn, In and Sn) studied by first-principles calculations

YbAl₃ is a potential thermoelectric (TE) material to be used in TE power generator utilizing waste heat sources. This work systematically investigated the alloying behavior of M in YbAl_3−xM_x (M = Mg, Cu, Zn, In and Sn) and their electronic structures by first-principles calculations. The solubility of alloying elements M and phase stability of YbAl_3−xM_x were studied by analyzing the elastic constants, formation and cohesive energies. The results show that Mg, In and Sn are the effective alloying elements for preparing YbAl_3−xM_x solid solutions, which are helpful for improving TE properties of YbAl₃.     

Synthesis and magnetocaloric characterization of rapidly solidified ErMn2 melt-spun ribbons

We have fabricated melt-spun ribbons of nominal composition ErMn₂ and studied their phase constitution and magnetocaloric (MC) properties by X-ray diffraction, scanning electron microscopy (SEM), magnetization and heat capacity measurements. The major phase formed shows the MgZn₂-type hexagonal structure (C14-type); however, both XRD and SEM analyses revealed the formation of impurity phases (i.e., Er₆Mn₂₃ and ErMn₁₂). Ribbons exhibit a saturation magnetization of 149 Am²kg⁻¹ at 2 K and a Curie temperature of T_C = 15 K. A field-induced metamagnetic transition at very low critical magnetic fields was observed below 8 K that leads to a change of sign in the magnetic entropy change ΔS_M below this temperature (ΔS_M^peak = 2.5 Jkg⁻¹K⁻¹ at 2 K and 5 T). For a magnetic field change of 5 T (2 T) applied along the ribbon length, the samples show a large peak value of the magnetic entropy change ΔS_M^peak of −20.5 (−10.8) Jkg⁻¹K⁻¹, a full-width at half-maximum δT_FWHM for the ΔS_M(T) curve of 20 (12) K, and a maximum adiabatic temperature change ΔT_ad^max of 7.4 (3.6) K. The obtained results are compared with the reported in literature by other authors for bulk alloys.     

Effect of sintering temperature on the structure and magnetic properties of SmCo5/Fe nanocomposite magnets prepared by spark plasma sintering

Highly dense SmCo₅/Fe nanocomposite bulk magnets were prepared by spark plasma sintering of magnetic field-milled SmCo₅/Fe nanocrsytalline powders. The sintering experiments were conducted with varying temperatures of 973–1123 K. The resultant bulk materials had densities of 85–98% and mean grain sizes of 17–30 nm. The SEM analysis showed that the bulk samples prepared at higher sintering temperature exhibited dense and uniform microstructure. The XRD studies in complement with energy dispersive X-ray analysis revealed that the bulk magnets sintered at or above 1073 K exhibited Sm(Co,Fe)₅ as main phase, along with other secondary phases such as Sm₂(Co,Fe)₁₇ and α-Fe(Co). A single-phase behavior with high remanence ratios (0.67–0.77) for the nanocomposite magnets was demonstrated by the magnetic measurements. In the present study, the sintering temperature of 1073 K was found to be optimum in achieving relatively high coercivity (8.2 kOe), magnetization (97.5 emu/g) and energy product (278.7 kJ/m³) for the SmCo₅/Fe nanocomposite bulk magnets.     

EMF Study of the Liquid Sb-Sn-Zn Alloys

The measurement of electromotive force (EMF) of concentration cells was applied to obtain zinc activity in ternary liquid Sb-Sn-Zn alloys in a Zn_liq|(KCl-LiCl)_eut + ZnCl₂|(Sb-Sn-Zn)_liq galvanic cell. The measurements were carried out at temperatures from 723 up to 943 K for different Zn concentrations X _Zn and for five constant ratios of Sn to Sb mole fractions, which were 1/3, 1, 3, 4 and 9. It was found out, that with increasing Sn concentration in the ternary alloys, the activity of Zn grew reaching the highest values for alloys of ratio Sn/Sb = 9 out of the ternary alloys examined. The observed straight-line changes of EMF matched a EMF = A + B * T equation. The calculated coefficients served to obtain the activities and excess Gibbs free energy for selected temperatures 823 and 923 K.     

Microstructure,phase evolution and magnetic properties of melt-spun SmCo6.8−xSnxZr0.2 (x = 0, 0.1 and 0.3) ribbons

SmCo_6.8?xSn_xZr_0.2 (x = 0, 0.1 and 0.3) melt-spun ribbons have been produced from bulk as-cast samples by varying wheel speeds from 8 to 32 m/s. The microstructure, phase evolution and magnetic properties of as-spun ribbon samples were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and vibrating sample magnetometer (VSM), respectively. The XRD results show that the addition of Sn to SmCo_6.8Zr_0.2 alloy has significant role to shift the TbCu₇-structure into Sm₂Co₁₇(H) and Sm₂Co₁₇(R) -phases for the Sn content of 0.1 and 0.3, respectively. The SEM analysis reveals that the grain size of the as-spun ribbon samples is gradually refined from several microns to 600?800 nm with the increase of wheel speed from 8 to 32 m/s. A wheel speed of 24 m/s has been found to be optimal in achieving reasonably good combination of coercivity (H_c) and magnetization (M_s) values in the as-spun SmCo_6.8-xSn_xZr_0.2 (x = 0, 0.1 and 0.3) ribbons. Maximum values of H_c of 5.1 kOe and M_s of 76.9 emu/g were achieved for the SmCo_6.5Sn_0.3Zr_0.2 ribbons spun at 24 m/s; upon annealing at 550 °C, the H_c values of these ribbons were significantly improved (10.4 kOe) with not much destruction in the M_s value.     

On the RMgSn rare earth compounds

A new family of ternary rare earth compounds, RMgSn, has been synthesized and their crystal structures, formation thermodynamics and melting behavior have been studied. All of the rare earth elements (including Y) form the 1:1:1 equiatomic phase with Mg and Sn. These compounds crystallize with two different structure types: the RMgSn phases with the light R (R = La, Ce and Pr) adopt the orthorhombic TiNiSi structure type (an ordered derivative of the Co₂Si-type structure, oP12, space group Pnma), while the ones formed by the heavier R (R = Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm and Lu, plus Y) have the tetragonal CeScSi-type structure (an ordered derivative of the La₂Sb-type structure, tI12, space group I4/mmm). The observed unit cell volume V_obs and the mean atomic volume V_obs/n (where n is the number of atoms in a unit cell) both decrease as expected due to the lanthanide contraction, but following different trends. The volume of formation (ΔV%) becomes more negative on going from La to Lu along the series.All phases have been found to form congruently (including YMgSn and probably LuMgSn). Their melting temperatures decrease from La to Lu, but with different slopes for the two different structure types.Relationships, between the volume of formation and also the melting points with the lanthanide contraction have been examined. The relationship between the former is anomalous compared to that observed for other R_xM_y series of compounds, while the latter relationship is consistent with previously published results.     

Nanocrystallinity and magnetic property enhancement in melt-spun iron-rare earth-base hard magnetic alloys

Refinement of the grain size below ~35 nm mean diameter in melt-spun FeNdB-base alloys leads to en-hancement of remanent polarization,J _r, above the level predicted by the Stoner-Wohlfarth theory for an aggregate of independent, randomly oriented, and uniaxial magnetic particles. This article summarizes the results of the recent systematic research on this phenomenon, including the influence of alloy compo-sition and processing conditions on the crystallite size, degree of enhancement ofJ _r, and maximum en-ergy product(BH) _max. It has been shown that the effect can also occur in ternary FeNdB alloys, without the addition of silicon or aluminum, which was originally thought necessary, providing the nanocrystal-lites are not magnetically decoupled by a paramagnetic second phase. Values of(BH) _max above 160 kJ m_-3 have been achieved. The relationship between grain size,J _r, intrinsic coercivity,_JHc, and(BH) _max are discussed in terms of magnetic exchange coupling, anisotropy, and other parameters. Recent exten-sion of this work to the enhancement of properties in Fe-Mischmetal-Boron-base alloys and to bonded magnets with a nanocrystalline structure is also described.     

Tb doped CoNbZr soft magnetic films with high anisotropy field for applications in GHz frequency region

CoNbZr films for an adjustable magnetic anisotropy field H_k by doping with rare-earth of different atomic ratio Tb element were obtained in this work. The effect of Tb addition ranged from 0 to 4 at.% on the magnetic properties of the amorphous CoNbZr films was further investigated. The results show that the magnetic anisotropy field H_k increases sharply with the addition of Tb while the coercivity H_ch along the hard axis and H_ce along the easy axis change slightly with increasing Tb content in the films. As a consequence, CoNbZr film doped with 2 at.% of Tb exhibits excellent soft magnetic properties with a saturation magnetization 4πM_s of 8.9 kG, a hard axis coercivity H_ch of 1.79 Oe, a easy axis coercivity H_ce of 1.4 Oe and a magnetic anisotropy field H_k of 87 Oe. The measured ferromagnetic resonance frequency f_FMR of this film is 2.30 GHz. The real permeability μ′ is about 100, which is maintained up to 2 GHz. In addition, there is a broad band of the imaginary permeability μ″ over a large frequency band, indicating high losses. Therefore, Tb doped CoNbZr film is an excellent candidate for high frequency applications such as electromagnetic interference suppressors.     

MnFeNiCuPt and MnFeNiCuCo high-entropy alloys designed based on L10 structure in Pettifor map for binary compounds

Quinary exact equi-atomic MnFeNiCuPt and MnFeNiCuCo alloys were investigated to examine their formation of high-entropy alloys (HEAs) by focusing on an L1₀ structure from Pettifor map for binary compounds with 1:1 stoichiometry. The MnFeNiCuPt alloy was practically selected through computer-assisted alloy design under conditions of ≤ 20 at% noble metals, and the condition that the L1₀ structure appears as frequently as possible in the constituent binary equi-atomic compositions comprised of 78 elements. MnFeNiCuCo was selected by substituting Pt with Co from the MnFeNiCuPt alloy as the second candidate. X-ray diffraction and observations by scanning electron microscopy (by energy dispersive spectroscopy for composition analysis) revealed that as-prepared MnFeNiCuPt and MnFeNiCuCo alloys were formed into HEAs with dual fcc structures containing dendrites of ∼10 μm in width. The MnFeNiCuPt and MnFeNiCuCo alloys annealed at 1373 K for 43.2 ks and subsequently quenched in water formed single fcc phases and dual fcc phases, respectively. The annealed MnFeNiCuPt and MnFeNiCuCo alloys were subsequently cooled in a furnace and formed single L1₂ ordered phases and dual fcc phases, respectively. These phases, experimentally observed in the annealed samples, could be partially explained by thermodynamic calculations using Thermo-Calc with SSOL4 and SSOL5 databases for solid solutions. The MnFeNiCuPt and MnFeNiCuCo alloys exhibit soft magnetism with saturation magnetization of 0.23 and 0.43 T, respectively, with coercivity values of ∼1 kA m⁻¹. An alloy design for HEAs based on digitalized crystallographic data of these samples could lead to the discovery of new HEAs.     

Magnetic property and magnetocaloric effect in TmCoAl compound

A large reversible magnetocaloric effect accompanied by a second order magnetic phase transition from paramagnetic (PM) to ferromagnetic (FM) has been observed in TmCoAl intermetallic compound. For the magnetic field change of 5 T, the maximum value of magnetic entropy change (−ΔS_M^max) and the value of refrigerant capacity (RC) are evaluated to be 18.2 J/kg K and 211 J/kg, respectively. In particular, a large −ΔS_M^max (10.2 J/kg K) is achieved at 7.5 K under a low magnetic field change from 0 to 2 T with no thermal hysteresis and magnetic hysteresis loss. The large reversible magnetocaloric effect (both the large −ΔS_M and the high RC) indicates that TmCoAl is one of a promising material for magnetic refrigeration in low temperature.