Structure and magnetic properties of (Nd,Dy)16(Fe,Co)76−xTixB8 powders prepared by mechanical alloying

Nanocrystalline (Nd,Dy)₁₆(Fe,Co)_76−xTi_xB₈ magnets were prepared by mechanical alloying and respective heat treatment at 973–1073 K/30–60 min. An addition of 0.5 at % of Ti results in an increase of coercivity from 796 to 1115 kA m⁻¹. Partial substitution of Nd by Dy results in an additional increase of coercivity up to 1234 kA m⁻¹. Mössbauer investigations shows that for x?1 the (Nd,Dy)₁₆(Fe,Co)_76−xTi_xB₈ powders are single phase. For higher Ti contents (x>1) the mechanically alloyed powders heat treated at 973 K are no more single phase, and the coercivity decreases due to the presence of an amorphous phase. A heat treatment at a higher temperature (1073 K) for longer time (1 h) results in the full recrystallisation of powders. The mean hyperfine field of the Nd₂Fe₁₄B phase decreases for titanium contents of 0?x?1, and remains constant for x>1. This indicates that the Ti content in the Nd₂Fe₁₄B phase reaches its maximum value.     

Structural and magnetic properties of hydrides R3Fe29−xVxHy (R=Y, Ce, Nd, Sm, Gd, Tb, and Dy)

A systematic investigation of crystallographic and intrinsic magnetic properties of the hydrides R₃Fe_29−xV_xH_y (R=Y, Ce, Nd, Sm, Gd, Tb, and Dy) has been performed in this work. The lattice constants , and c and the unit cell volume of R₃Fe_29−xV_xH_y decrease with increasing rare-earth atomic number from Nd to Dy, except for Ce, reflecting the lanthanide contraction. Hydrogenation results in regular anisotropic expansions along the a-, b-, and c-axes in this series of hydrides. Abnormal crystallographic and magnetic properties of Ce₃Fe_27.5V_1.5H_6.5, like Ce₃Fe_27.5V_1.5, suggest that the Ce ion is non-triply ionized. Hydrogenation leads to the increase in both Curie temperature for all the compounds and in the saturation magnetization at 4.2 K and RT for R₃Fe_29−xV_x with R=Y, Ce, Nd, Sm, Gd, and Dy, except for Tb. Hydrogenation also leads to a decrease in the anisotropy field at 4.2 K and RT for R₃Fe_29−xV_x with R=Y, Ce, Nd, Gd, Tb, and Dy, except for Sm. The Ce₃Fe_27.5V_1.5 and Gd₃Fe_28.4V_0.6 show the larger storage of hydrogen with y=6.5 and 6.9 in these hydrides.     

Structure and magnetostriction of RFex (1.6 ? x ? 2.0) and R(Fe1−yTiy)1.8 (y ? 0.2) alloys (RDy0.65Tb0.25Pr0.1)

Structure, Curie temperature and magnetostriction of RFe_x (1.6 ? x ? 2.0) and R(Fe_1−yTi_y)_1.8 (y ? 0.2) alloys (RDy_0.65Tb_0.25Pr_0.1) have been investigated using optical microscopy, X-ray diffraction, AC initial susceptibility and standard strain gauge techniques. The homogenized RFe_x alloys are found to be essentially single phase in the range of 1.8 ? x ? 1.85. The second phase is a rare-earth-rich phase when x ? 1.8, and (Dy, Tb, Pr)Fe₃ phase when x ? 1.85. X-ray diffraction indicates that the R(Fe_1−yTi_y)_1.8 alloys contain a small amount of Fe₂Ti phase when y ? 0.05, which increases with the increment of Ti content. The Curie temperature of R(Fe₁−_yTi_y)_1.8 alloys slightly enhances with increasing Ti concentration when y ? 0.05, then remains almost unchanged in the range of 0.05 ? y ? 0.20. The magnetostriction of RFe_x alloys is improved when x ? 1.80 and reduced by increasing Fe content when x ? 1.85. The magnetostriction of R(Fe_1−yTi_y)_1.8 alloys is lowered by increasing Ti content.     

Nd1.9M0.1Fe12Co2B,M = Ti or Hf as a material for permanent magnets

Magnetic properties (saturation magnetizations, anisotropy fields and Curie temperatures) of the alloys of the composition Nd_1.9M_0.1Fe₁₂Co₂B, with M = Ti and Hf are presented. All of the compounds crystallize in the tetragonal Nd₂Fe₁₄B structure. With substitution of Nd by Ti or Hf, the saturation moment and Curie temperature decrease, but the anisotropy fields, H_A, are found to increase significantly. Theoretical energy products are reduced from 65 to 63 MGOe when Nd is replaced by Ti or Hf to the extent of x = 0.1.     

Structure and magnetostriction of RFex (1.6 x 2.0) and R(Fe1−yTiy)1.8 (y 0.2) alloys (R=Dy0.65Tb0.25Pr0.1)

Structure, Curie temperature and magnetostriction of RFe_x (1.6 x 2.0) and R(Fe_1−yTi_y)_1.8 (y 0.2) alloys (R=Dy_0.65Tb_0.25Pr_0.1) have been investigated using optical microscopy, X-ray diffraction, AC initial susceptibility and standard strain gauge techniques. The homogenized RFe_x alloys are found to be essentially single phase in the range of 1.8 x 1.85. The second phase is a rare-earth-rich phase when x 1.8, and (Dy, Tb, Pr)Fe₃ phase when x 1.85. X-ray diffraction indicates that the R(Fe_1−yTi_y)_1.8 alloys contain a small amount of Fe₂Ti phase when y 0.05, which increases with the increment of Ti content. The Curie temperature of R(Fe₁−_yTi_y)_1.8 alloys slightly enhances with increasing Ti concentration when y 0.05, then remains almost unchanged in the range of 0.05 y 0.20. The magnetostriction of RFe_x alloys is improved when x 1.80 and reduced by increasing Fe content when x 1.85. The magnetostriction of R(Fe_1−yTi_y)_1.8 alloys is lowered by increasing Ti content.     

Structure,magnetic properties and magnetostriction of laves compounds Nd1−xPrx(Fe0.35Co0.55B0.1)2

The C15 Laves phases with composition Nd_1−xPr_x(Fe_0.35Co_0.55B_0.1)₂ (0?x?1) have been synthesized by arc melting and subsequent annealing. The Curie temperature T_c and the saturation magnetizations M_s at 5 and 295 K decrease with increasing Pr content. The linear anisotropic magnetostriction λ_a=λ_∥−λ_⊥ at room temperature for Nd_1−xPr_x(Fe_0.35Co_0.55B_0.1)₂ alloys with 0?x?0.4 initially reaches a negative minimum, then increases and changes its sign with increasing magnetic field H, and the λ_a for the alloys with x?0.6 is positive and increases as magnetic field H increases.     

High magnetostriction at low fields of (Tb1−xDyx)0.2Pr0.8(Fe0.4Co0.6)1.88C0.05 intermetallic compounds

The structure and magnetostriction of the (Tb_1−xDy_x)_0.2Pr_0.8(Fe_0.4Co_0.6)_1.88C_0.05 intermetallic compounds (0≤x≤1) were studied by X-ray diffraction and magnetic measurements. The formation of an approximate single Laves phase with a MgCu2-type cubic structure was observed in this series of compounds. It was found that the Curie temperature and the saturation magnetization of the compounds would decrease with increase in the Dy content up to x=1. The magnetostriction λ_a (λ_a=λ_‖-λ_⊥) gently rises when x≤0.6, and follows with a precipitous fall when x exceeds 0.6, with the highest value of λ_a being reached in the compounds with x=0.6. The magnetostriction of all the samples was observed to approach their own saturation in the magnetic fields higher than 4 kOe. This indicates that the addition of a small amount of Dy could effectively improve the low-field magnetostriction of the Tb_0.2Pr_0.8(Fe_0.4Co_0.6)_1.88C_0.05 compounds, which could become a kind of promising magnetostrictive material.     

Effect of refractory metals addition on the structural and magnetic properties of Pr3(Fe, Co, Ti)29 system

Polycrystalline refractory metal-substituted Pr₃(Fe_0.6M_0.1Co_0.3)_27.5Ti_1.5 (M=V, Ti, Zr, Mo, Nb,Cr) and Pr₃(Fe_0.5Co_0.5)_27.5Ti_1.5 have been studied for high-temperature permanent magnetic materials. X-ray diffraction showed the main phase to be the 3:29 phase. We observed the highest reported T_C (Curie temperature) of 640 °C for the 3:29 system in the Pr₃(Fe_0.5Co_0.5)_27.5Ti_1.5. In the refractory metal-substituted systems, the highest T_C of 480 °C was observed for the Nb-substituted alloy. SEM measurements showed that Ti in Pr₃(Fe_0.6Ti_0.1Co_0.3)_27.5Ti_1.5 is deposited near the grain boundary. H_A (anisotropy energy) of V-substituted alloy is as high as 72 kOe, the highest reported in the 3:29 system and is ∼200% higher than 24 kOe observed in Pr₃(Fe_0.7Co_0.3)_27.5Ti_1.5. Cr and Ti substitutions show an increase of 65% (40 kOe) and 45% (35 kOe) in H_A respectively. M_S (saturation magnetization) values were ∼100 emu/g and are lower than that observed in Pr₃(Fe_0.7Co_0.3)_27.5Ti_1.5.     

Iron and molybdenum valences in double-perovskite (Sr,Nd)2FeMoO6: electron-doping effect

Double perovskite, (Sr_1−xNd_x)₂FeMoO₆, was doped with electrons through partial substitution of divalent Sr by trivalent Nd (0≤x≤0.2). The Fe valence and the degree of B-site order were probed by ⁵⁷Fe Mössbauer spectroscopy. Replacing Sr by Nd increased the fraction of Fe and Mo atoms occupying wrong sites, i.e. antisite disorder. It had very little effect on the Fe valence: a small but visible increase in the isomer shift was seen for the mixed-valent Fe^II/III atoms occupying the right site indicating a slight movement towards divalency of these atoms, which was more than counterbalanced by the increase in the fraction of antisite Fe atoms with III valence state. It is therefore argued that the bulk of the electron doping is received by antisite Mo atoms, which - being surrounded by six Mo^V/VI atoms-prefer the lower IV/V valence state. Thus under Nd substitution, the charge-neutrality requirement inflicts a lattice disorder such that low - valent Mo^IV/V can exist.     

快淬(Er1-xSmx)2Fe17Cy化合物的结构与磁性

用快速急冷方法制备了(Er_1-xSm_x)₂Fe₁₇C_y(x≤0.8,1.5≤y≤2.5)化合物,它们具有菱方Th₂Zn₁₇型结构,并且在高温是稳定的。与相应的不含C的(Er_1-xSm_x)₂Fe₁₇化合物比较,当C含量y=2.5时,引起单胞体积增加～6.3％,居里温度增     

Crystal structure and magnetic properties of Nd（Mn1-xFex）2Si2 compounds

X-ray powder diffraction,resistivity and magnetization studies have been performed on polycrystalline Nd(FexMn1-x)2Si2 (0 ≤ x ≤ 1) compounds which crystallize in a ThCr2Si2-type structure with the space group I4/mmm.The field-cooled temperature dependence of the magnetization curves shows that,at low temperatures,NdFe2Si2 is antiferromagnetic,while the other compounds show ferromagnetic behaviour.The substitution of Fe for Mn leads to a decrease in lattice parameters a,c and unit-cell volume V .The Curie temperature of the compounds first increases,reaches a maximum around x = 0.7,then decreases with Fe content.However,the saturation magnetization decreases monotonically with increasing Fe content.This Fe concentration dependent magnetization of Nd(FexMn1-x)2Si2 compounds can be well explained by taking into account the complex effect on magnetic properties due to the substitution of Mn by Fe.The temperature’s square dependence on electrical resistivity indicates that the curve of Nd(Fe0.6Mn0.4)2Si2 has a quasi-linear character above its Curie temperature,which is typical of simple metals.     

Structural and magnetic properties of Pr3(Fe1−xCox)27.5Ti1.5 (x=0.0, 0.1, 0.2, 0.3)

A novel class of Co-substituted 3 : 29 materials, Pr₃(Fe_1−xCo_x)_27.5Ti_1.5 (x=0, 0.1, 0.2, 0.3) have been synthesized. Rietveld analysis of X-ray powder diffraction patterns for the x=0, 0.1 and 0.2 compositions showed that nearly all of the compounds are formed in monoclinic symmetry, with A2/m space group with traces of α-Fe, whereas, in x=0.3, additional traces of a (Co/Fe)–Ti (1 : 12) phase are also seen. The saturation magnetization increases with Co concentration both at 5 and 300 K and is explained on the basis of a rigid band model. A magnetic transition is observed for x=0.1 near 240 K. A large increase in Curie temperature, of about 180 K for x=0.1 and about 110 K for the other concentrations, is discussed on the basis of the strengthening of TM–TM exchange by the preferential occupation of Co in some of the Fe sites originally participating in antiferromagnetic bonds.     

Effects of additives on hydrogen absorption and desorption characteristics of Nd(Fe,Mo)12 alloys

Effects of such additives as Co, Zr, Nb or Ga on hydrogen absorption and desorption characteristics of Nd(Fe,Mo)₁₂ alloys are investigated. It is found that Zr or Nb addition increases the disproportionation temperature of Nd(Fe,Mo)₁₂ alloys, and Co or Ga addition decreases the recombined temperature of its disproportionated products. This shows that Zr or Nb addition retards the disproportionation, while Co or Ga addition is effective for improving the recombination, which is similar to the effects of the additives on the hydrogen absorption and desorption characteristics of Nd₂Fe₁₄B alloys. However, according to X-ray diffraction (XRD) investigations for the magnetic-oriented samples, the final hydrogenation disproportiontation desorption recombination (HDDR) NdFe_10.5−XM_XMo_1.5 (M=Co, Zr, Nb or Ga) products are isotropic. The effects of additives on hydrogen absorption and desorption characteristics of Nd₂Fe₁₄B and Nd(Fe,Mo)₁₂ alloys are very similar, but the magnetic anisotropy of the final two HDDR products are different. In order to investigate this, similarities and differences of the two alloy systems and their corresponding HDDR phenomena are further studied. The results show that the formation of anisotropic powders may be related to the disproportionated products and crystal growth direction of the Nd₂Fe₁₄B and Nd(Fe,Mo)₁₂ system.     

Magnetic properties and magnetocaloric effect in Dy(Co1−xFex)2 alloys

Polycrystalline samples of Laves-phase alloys Dy(Co_1−xFe_x)₂(x=0$x=0$, 0.02,0.04,0.06,0.08) have been prepared by arc-melting method. No first order phase transition was observed for samples with x≠0$x\ne 0$. With the increase of Fe content, the Curie temperature increases greatly, while the calculated magnetic entropy change, ΔS_M, shows an obvious decrease with a broader peak. The origin of the magnetocaloric effect in Dy(Co_1−xFe_x)₂ alloys has been discussed.     

Structure and magnetic phase diagram of mixed rare-earth Nd1−xTbxFe10.5Mo1.5 compounds

The structural and magnetic properties of Nd_1−xTb_xFe_10.5Mo_1.5 (x=0$x=0$, 0.2, 0.4, 0.6, 0.8, 1.0) compounds have been investigated by means of X-ray diffraction and magnetic measurements. All the investigated compounds crystallize in the tetragonal ThMn₁₂-type structure with I4/mmm space group. The lattice parameters a, c and the unit-cell volume V decrease with increasing x. The Curie temperatures T_C are almost independent x. There exists a unique spin-reorientation transition for the end compositions of Nd_1−xTb_xFe_10.5Mo_1.5 compounds with x=0$x=0$ and x=1$x=1$, while two spin-reorientation transitions are observed for x=0.2–0.8$x=0.2–0.8$. The room-temperature magnetocrystalline anisotropy of Nd_1−xTb_xFe_10.5Mo_1.5 compounds changes from uniaxial to planar with increasing x content. Based on magnetic measurements, a magnetic phase diagram of Nd_1−xTb_xFe_10.5Mo_1.5 compounds is constructed. By minimizing the magnetocrystalline anisotropy energy, a theoretical magnetic phase diagram for the Nd_1−xTb_xFe_10.5Mo_1.5 system is derived, showing a reasonable agreement with the observations.     

MAGNETIC PROPERTIES AND CRYSTALLIZATION OF THE RAPIDLY QUENCHED (Fe1-xNdx) 81.5B18.5 ALLOYS

Magnetic properties and crystallization behaviors of amorphous (Fe_1-xNd_x) _81.5B_18.5 alloys were studied. The crystallization temperature is found to rise at first and then drop monotonically with x, having a maximum value of 976K at x=0.11 (9at% Nd). The (Fe_1-xNd_x) _81.5B_18.5 alloys prepared at a quenching rate of v_s = 6.6m /s are amorphous, and exhibit good glass formability. Both the coercive field H_c and energy product (BH)_max depend strongly on Nd concentration. Amorphous (Fe_1-xNd_x) _81.5B_18.5 alloys with higher Nd concentration have a high coercive field at low temperature, due to the large random uniaxial anisotropy of Nd. The room-temperature H_c and (BH)_max obtained on optimal annealing con-ditions show two maxima as a function of Nd concentration x. The highest room-temperature coercive field H_c =22 kOe within the Nd concentrations around x=0.368 and the maximum energy product(RH)_max= 13.3 MG·Oe at x =0.055 are observed. The hard magnetic properties of these crystallized samples are related to the presence of the bard magnetic Nd₂Fe₁₄B phase.     

R3(Fe,Mo)29Nx的晶体学特性和内禀磁性

研究了R₃(Fe,Mo)₂₉(R=Ce,Nd,Sm,Gd,Tb,Dy,Y)氮化物的晶体学特性和内禀磁性.主要研究内容为：氮化对R₃(Fe,Mo)₂₉金属间化合物的点阵参数、居里温度T_C、饱和磁化强度σ_s和各向异性场B_a的影响. 关键词：     

R2(Fe1-xAlx)14B的内禀磁性和永磁性能(R=Nd和Y)

本文研究了Al在R₂(Fe_1-xAl_x)₁₄B多元合金中的固溶度(R=Nd和Y),当x<0.1时,可形成四方结构。研究了在此类合金中,饱和磁化强度、居里温度、磁晶各向异性等内禀磁性,以及矫顽力和磁能积等永磁性能随Al含量的变化。发现以Al代换Fe时,使铁次点阵的磁晶各向异性出现极值;同时以Al代换Fe时,可使磁体的矫顽力显著提高。以Co和Al同时对Fe进行代换,制造成分约为Nd_16.5B _关键词：     

Magnetic transitions and magnetostrictive properties of Laves compounds Sm0.88Nd0.12(Fe1−xCox)1.93

The structure, magnetic and magnetostrictive properties of Sm_0.88Nd_0.12(Fe_1−xCo_x)_1.93 (0≤x≤1.0) alloys have been investigated. The alloys have the cubic MgCu₂ structure over the whole composition range and the lattice parameter a decreases with increasing x. For 0≤x≤0.2, substitution of Co for Fe slightly increases the saturation magnetization M_s and Curie temperature T_c, while further substitution causes a decrease in both M_s and T_c. The spin reorientation is observed, and a phase diagram for the spin configurations of the Sm_0.88Nd_0.12(Fe_1−xCo_x)_1.93 system is determined. The spontaneous magnetostriction λ₁₁₁ increases as x is increased, while a monotonic decrease of the saturation magnetostriction λ_s with x originates from the increase of λ₁₀₀ with opposite sign to that of λ₁₁₁, which may be caused by the filling of the d band due to Co substitution.     

Enhancement of magnetocaloric effects in La0.8R0.2(Fe0.919Co0.081)11.7 Al1.3 (R=Pr, Nd) compounds

The magnetic properties and magnetocaloric effects (MCEs) in La_0.8R_0.2(Fe_0.919Co_0.081)_11.7Al_1.3 (R=Pr, Nd) compounds have been investigated. When Pr and Nd substitute for La, the Curie temperature of compounds decreases. The values of the MCEs are enhanced significantly by a partial substitution of Nd for La. Under the field change of 2 and 5 T, the maximum magnetic entropy changes for La_0.8Nd_0.2(Fe_0.919Co_0.081)_11.7Al_1.3 compound are −4.56 and −9.46 J/Kg K, respectively. It can be exploited for room temperature magnetic refrigeration material.