原子团Fe4B的电子结构

利用多重散射X_α自洽场法,对取为四面体的原子团Fe₄B的电子结构进行计算,分析、对比原子团Fe₄与Fe₄B的能级分布、轨道等高线图和态密度的分布,讨论B原子加入对原子团Fe₄B的电子结构的影响,并结合讨论了非晶态Fe₈₀B₂₀等合金的一些性质。 关键词：     

Electrical resistivity of amorphous metallic glasses Fe80B80 and Fe78Mo2B20 between 78 and 1000 K

Electrical resistivity (ρ) of amorphous Fe₈₀B₂₀ and Fe₇₈Mo₂B₂₀ have been studied as a function of temperature (T) between 78 and 1000 K. The ρ vs T curves, obtained with specified warming and cooling rates, show that such curves are sensitive probes of the crystallization process. Within the experimental error, no anomalies in the ρ behavior can be seen at the Curie temperature of each amorphous alloy.     

Fe65B22Nd9Mo4 bulk nanocomposite permanent magnets produced by crystallizing amorphous precursors

The Fe₆₅B₂₂Nd₉Mo₄ nanocomposite permanent magnets in the form of a rectangular cross sectioned rod have been prepared by annealing the amorphous precursors. The thermal behavior, structure and magnetic properties of the magnets have been investigated by differential scanning calorimetry, X-ray diffractometry, electron microscopy and magnetometry techniques. The as-cast Fe₆₅B₂₂Nd₉Mo₄ alloy showed soft magnetic properties, which changed into magnetically hard after annealing. Results provoke that the magnetic properties of the alloy are sensitive to thermal processing conditions. The optimum hard magnetic properties with a remanence (B_r) of 0.56 T, coercivity (_iH_c) of 920.7 kA/m and maximum energy product (BH)_max of 50.15 kJ/m³ were achieved after annealing the alloy at 983 K for 10 min. The good magnetic properties of Fe₆₅B₂₂Nd₉Mo₄ magnets are ascribed to the exchange coupling between the nano-scaled soft α-Fe, Fe₃B and hard Nd₂Fe₁₄B magnetic grains.     

Hyperfine field distribution in amorphous Fe40Ni40B20

From the Mössbauer investigation of amorphous Fe₄₀Ni₄₀B₂₀ and Fe₈₀B₂₀ alloys it was found that the substitution of Fe by Ni only shifts but does not influence the shape of the iron hyperfine field distribution contrary to that of crystalline f.c.c. Ni-Fe alloys suggesting a rather localized type of behaviour. The distributions of the linear combinations of isomer shift and quadrupole splitting are affected by this substitution.     

Effect of carbon substitution on the specific heat of Fe80B20−xCx (0≤x≤8)

The specific heat of ferromagnetic metallic glasses Fe₈₀B_20?xC_x (0≤x≤8) has been measured in the temperature range between 1.5 and 10 K. It is found that the electronic specific heat coefficient is independent of the carbon concentration x. The Debye temperature has a broad peak around x = 4. Both these results are in sharp contrast to the case of FeB binary metallic glasses and could be qualitatively understood in terms of magnetic and structural properties.     

Stoner excitations in the strong itinerant amorphous ferromagnets FexNi80−xB18Si2 and Fe80B20

Accurate measurements of the static magnetization of the amorphous ferromagnets Fe_xNi_80?xB₁₈Si₂ (x = 15, 20, 40, 60%) and Fe₈₀B₂₀ are reported. The results are analyzed in terms of spin-wave and Stoner excitations, and the latter indicate strong itinerant ferromagnetism with a Stoner gap Δ varying between 20 and 60 K. The other fitting parameters give values of the spin-wave stiffness and a quantity simply related to the saturation magnetization. The well-known anomaly regarding the spin-wave stiffness observed in earlier measurements in thus explained quantitatively.     

Synthesis and magnetic properties of Au-coated amorphous Fe20Ni80 nanoparticles

Gold-coated nanoparticles of Fe₂₀Ni₈₀ (permalloy) have been synthesized by a microemulsion process. The as-prepared samples consist of ∼5 nm diameter particles of amorphous Fe₂₀Ni₈₀ that are likely encapsulated in B₂O₃. One or more Fe₂₀Ni₈₀@B₂O₃ particles are subsequently encapsulated in 8-20 nm gold nanospheres, as determined by TEM and X-ray powder diffraction (XRD) line broadening. The gold shells were found to be under expansive strain. Magnetic data confirm the existence of a superparamagnetic phase with a blocking temperature, T_B, of ∼33 K. The saturation magnetization, M_S, of the as-prepared, Au-coated sample is ∼65 emu g⁻¹ at 5 K and ∼16 emu g⁻¹ at 300 K. The coercivity, H_C, is ∼280 Oe at 5 K.     

Die-upset Nd11.5Fe72.4Co9Nb1B6.1 magnets with additions of Zn, Al and Sn

The magnetic properties and microstructure were studied for bulk Nd_11.5Fe_72.4Co₉Nb₁B_6.1 magnets synthesized by hot-pressing and subsequent die-upsetting the melt-spun ribbons with additions of three kinds of low-melting-point metal (Zn, Al and Sn). Die-upset Nd_11.5Fe_72.4Co₉Nb₁B_6.1 magnets have low magnetic properties since they have an inhomogeneous microstructure with many coarse grains. The microstructure of die-upset magnets remains almost unchanged with Al and Sn additions, which only have negative effects on the magnetic properties. Different from Al and Sn additions, Zn addition changes the phase composition of the starting melt-spun powers due to the reaction of Zn and Nd₂Fe₁₄B during hot-pressing and hot-deforming and enhances the development of the desired [0 0 1] texture and improves the microstructure of die-upset magnets. As a result, an anisotropic magnet with good maximum energy product (221 kJ/m³) and high coercivity (670 kA/m) is obtained by adding 2 wt% Zn to the Nd_11.5Fe_72.4Co₉Nb₁B_6.1 alloy.     

Fe80B20,Fe80Si6B14金属玻璃中近邻原子间的相互作用

用转靶X射线源及弯晶EXAFS谱仪测定了Fe₈₀B₂₀及Fe₈₀Si₆B₁₄金属玻璃中铁的X射线K吸收谱。由EXAFS谱确定了两种金属玻璃的近邻结构参量。此外,通过测定XANES谱并与纯铁及其有关的化合物Fe₂B,FeB中铁的XANES比较发现:吸收边能量、“白线”结构等均出现一些变化,表明两种金属玻璃的近邻原子Fe-B,Fe-Si以及Fe-Fe之间的相互作用比铁与硼所形成的稳定化合物中要强,这对于决定金属玻璃的短程序结构具有重要的作用。 关键词：     

57Fe Mössbauer study of amorphous Fe81B13.5Si3.5C2

The amorphous ferromagnet Fe₈₁B_13.5Si_3.5C₂ (Metglas^® 2605SC) has been investigated with Mössbauer spectroscopy. The hyperfine interaction parameters are studied between 80 and 300 K from which some characteristic properties are deduced. The behaviour of the amorphous alloy at higher temperatures has been studied by the room temperature spectra of annealed samples. After a structural relaxation process, a two step crystallization transformation is observed leading to Fe-Si alloy and Fe₂(B, C). X-ray diffraction of samples annealed at higher temperatures reveals the presence of an orthorhombic Fe-B-Si phase of which the structure changes slightly with annealing temperature.     

Irradiation effects in amorphous alloy Fe80B20

The Mössbauer effect has been used to study the irradiation effects in the amorphous alloy Fe₈₀B₂₀ after 40 keV helium ion bombardment. Conversion electron Mössbauer spectroscopy reveals the eminent irradiation effects; α-iron phase appears in the damaged region of the sample.     

Structure, stability and magnetic properties of the Fe3O4(1 1 0) surface: Density functional theory study

Six surface models for the Fe₃O₄(1 1 0) surface were studied using the density functional theory (DFT), namely the AB-terminated surface (AB model), the AB-terminated with Fe_A vacancy (AB-Fe_A vac model), the AB-terminated with Fe_B vacancy (AB-Fe_B vac model), the B-terminated surface (B model), the B-terminated surface with Fe_B vacancy (B-Fe_B vac model), and the B-terminated surface with O vacancy (B-O vac model). Here, A and B denoted the Fe cations in tetrahedrally (Fe_A) and octahedrally (Fe_B) coordinated interstices. The stability, the electronic structure and the magnetic properties of the six surface models were also calculated. The results predict that the B-O vac model is more stable than other surface models. The half-metallic property remains in the AB and B models, while the other four surface models exhibit metallic properties. At the same time, the AB, AB-Fe_A vac, AB-Fe_B vac, B and the B-Fe_B vac models have ferrimagnetic properties, while the B-O vac model has antiferromagnetic property.     

高Br纳米晶Fe73.5Cu1Nb3Si13.5B9合金的损耗行为

在f=10—20000Hz和B_m=0.1—1.0T范围内,测量了高B_r纳米晶Fe_73.5Cu₁Nb₃Si_13.5B₉合金的损耗.把总损耗分离为磁滞损耗、经典涡流损耗和过剩损耗.测量结果表明,每周损耗随频率的变化表现出明显的非线性行为.用Bertotti的损耗统计理论描述了这种非线性行为.大致在两个频率范围内,有两种不同的描述方式. 关键词：     

Magnetic properties of amorphous ferromagnet Fe78Mo2B20

Low-field magnetic susceptibility and the magnetic field dependence of magnetization of Metglas 2605 A (Fe₇₈Mo₂B₂₀) were studied between 300 and 600 K and in fields up to 10kG. It is shown here that for an amorphous ferromagnetic alloy, the various methods of determination of Curie temperature T_c give the same value, which in this case is (564 ± 1) K. The critical exponent γ is 1.7 ± 0.1. Our low-field susceptibility measurements on Metglas 2605 (Fe₈₀B₂₀) gives a T_c of (634 ± 3) K while the reported high-field method value is 647 K. These results are discussed in terms of crystallization temperatures.     

Structural,microstructural and magnetic properties of nanocomposite isotropic Sm(CobalFe0.1MyZr0.04B0.04)7.5 ribbons with M=Ni,Cu and y=0.09 and 0.12

In boron-substituted melt-spun Sm(Co,Fe,Cu,Zr)_7.5-type alloys a nanocomposite microstructure and high coercivities in both as-spun and short-time annealed ribbons can be obtained. In the present study three different compositions, namely Sm(Co_0.73Fe_0.1Cu_0.09Zr_0.04B_0.04)_7.5, Sm(Co_0.70Fe_0.1Cu_0.12Zr_0.04B_0.04)_7.5 and Sm(Co_0.70Fe_0.1Ni_0.12Zr_0.04B_0.04)_7.5 have been examined in order to investigate the influence of composition on the magnetic properties and the microstructure. Melt-spun ribbons have been obtained and annealing has been followed under argon atmosphere for 30–75 min at 600–870 °C. For the as-spun ribbons the TbCu₇-type of structure and fcc-Co as a secondary phase have been identified in the X-ray diffraction patterns. For the annealed ribbons above 700 °C the 1:7 phase transforms into 2:17 and 1:5 phases. The TEM studies have shown a homogeneous nanocrystalline microstructure with average grain size of 30–80 nm. Coercivity values of 15–27 kOe have been obtained from hysteresis loops traced in non-saturating fields. The coercivity decreases with temperature, but it is sufficiently large to maintain values higher than 5 kOe at 380 °C.     

Synthesis, structural and magnetic properties of the nanocomposite Fe63B23Nd7Y3Nb3Cr1 magnets

The Fe₆₃B₂₃Nd₇Y₃Nb₃Cr₁ nanocomposite magnets in the form of sheets have been prepared by copper mold casting technique. The phase evolution, crystal structure, microstructural and magnetic properties have been investigated in the as-cast and annealed states. The as-cast sheets show magnetically soft behaviors which become magnetically hard by thermal annealing. The optimal annealed microstructure was composed of nanosize soft magnetic α-Fe (19-29 nm) and hard magnetic Nd₂Fe₁₄B (45-55 nm) grains. The best hard magnetic properties such as intrinsic coercivity, _jH_c of 1119 kA/m, remanence, B_r of 0.44 T, magnetic induction to saturation magnetization ratio, M_r/M_s=0.61 and maximum energy product, (BH)_max of 55 kJ/m³ was obtained after annealing at 680 °C for 15 min. The annealing treatment above 680 °C results in non-ideal phase grains growth, which degrade the magnetic properties.     

Transversal magnetic field effect on Fe40Ni40P14B6 amorphous alloys

A study about the influence of an electric current flowing through an amorphous ribbon Fe₄₀Ni₄₀P₁₄B₆ has been done. It has been found that the magnetization curves are strongly influenced by such a current (from 0 up to 5000 Hz). Bitter patterns under the action of the current have been observed in order to gain a better knowledge of these effects. The wall energy has been evaluated from a simple model.     

铁基纳米晶合金介观结构的等效RLC并联模型

根据实验研究成果提出纳米晶合金软磁性能受其介观结构影响的观点，建立了Fe基纳米晶合金的球状介观结构模型，分别求出只有交变磁场或交变磁场和静磁场作用时纳米晶粒球的频率函数——D函数.分析表明，两种D函数都是复变函数，其实部Re(D)为纳米晶电感性质和电容性质的反映，虚部Im(D)为纳米晶电阻性质的反映，据此建立了Fe基纳米晶合金介观结构的等效RLC并联模型.由该模型求得合金产生极值巨磁电阻的条件为v_extGMI=v|_Re(D)=0，决定因素有μ,σ,ω,R和H_ex及微观磁结构. 关键词： Fe基纳米晶合金 等效RLC并联模型 球状介观结构模型 频率函数     

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.     

Thermomagnetic and transport properties of metglas 2605 SC and 2605

Thermomagnetic and transport properties of Metglas 2605 (Fe₈₁B_13.5Si_3.5C₂) and 2605 (Fe₈₀B₂₀) have been studied in order to find out the results of partial replacement of one metalloid by others. It is concluded that 2605 SC is more stable than 2605 as an amorphous ferromagnet. The thermomagnetic properties are seriously affected by the replacement of B by Si and C while the transport properties have changed only quantitatively.