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     

Structure and soft magnetic properties of FINEMET type alloys: Fe73.5Si13.5Nb3 − x Mo x B9Cu1 (x = 1.5, 2)

FINEMET type ribbons (Fe_73.5Si_13.5Nb_3???xMo_xB₉Cu₁, x = 1.5, 2 at.%) were produced by the planar flow casting technique and subsequently heat treated at 823 K to induce nanocrystallization and to optimize its soft magnetic properties. The coercivity, measured by conventional fluxmetric method, resulted in H _C?=?0.53 ±0.10 and 0.41±0.05 A/m for x?=?1.5 and 2 respectively. A correlation between magnetic properties and the amorphous and nanocrystalline phases when Nb was partially substituted with Mo was studied by means of Mössbauer spectroscopy and X-ray diffraction.     

退火加热速度对Fe-Cu-Nb(V)-Si-B纳米晶合金磁性的影响

研究了退火温度为550℃的纳米晶化过程中加热速度对Fe_72.7Cu₁Nb₂V_1.8Si_13.5B₉与Fe_73.5Cu₁Nb₃Si_13.5B₉合金磁性的影响．磁性测量结果表明，退火加热速度对这两种合金软磁性能有明显的影响，快速加热可显著提高合金的初始磁导率μ_{i 关键词：}     

Fe-Cu-Nb-Si-B纳米晶体软磁材料中有效磁各向异性的测定

研究了成分为Fe_73.5Cu₁Nb₃Si_13.5B₉的纳米晶体结构的软磁材料的磁各向异性。理论分析及测量结果说明,用趋近饱和的磁化过程可以测定出这种材料中的有效磁各向异性常数,它比晶粒中的磁晶各向异性常数K₁约小一个数量级。 关键词：     

Moessbauer Study of Magnetic Structure in Fe-Based Nanocrystalline Alloys for MI Effect

The magneto-impedance effect in Fe-based nanocrystalline Fe₇₃Cu₁Nb_1.5Mo₂Si_13.5B₉ alloys has been observed. The results showed that the field dependence of the MI ratio was strongly influenced by the transverse magnetic structure in samples, which was demonstrated by Moessbauer spectroscopy. This revised version was published online in August 2006 with corrections to the Cover Date.     

Effect of the addition of Ge to the FINEMET alloy

The results obtained by partially substituting Ge for B and Si in the FINEMET alloy for the purpose of improving its magnetic properties at high temperatures are presented in this work. Nanocrystalline ribbons were obtained from controlled crystallization of amorphous material made employing the melt spinning technique. The studied compositions were: Fe_73.5Si_13.5Ge₂Nb₃B₇Cu₁ and Fe_73.5Si_13.5Ge₄Nb₃B₅Cu₁. The structural evolution of these alloys was studied using X-ray diffraction (XRD) and differential scanning calorimetry (DSC) and these results were correlated with their magnetic properties at different annealing temperatures. The coercivity obtained for both alloys was below 1 A/m at anneling temperatures between 773 and 823 K. The amorphous saturation magnetization was satisfactory, almost 137 emu/g, comparable with that obtained for FINEMET alloys. The nanocrystallization and the Curie temperatures are dependent on Ge concentration.     

Atmospheric corrosion of different Fe-based alloys in nanocrystalline state

Nanocrystalline Fe-based alloys are interesting for their soft magnetic properties. Because these alloys are potentially applicable in outdoor-working components, their corrosion behaviour requires careful analysis. This work presents the results of the atmospheric corrosion tests in industrial and rural environments performed for up to 6 months. We compared the corrosion behaviour of two different compositions of NANOPERM-type alloys: Fe_87.5Zr_6.5B₆ and Fe₇₆Mo₈Cu₁B₁₅ with classical FINEMET alloys of the nominal composition of Fe_73.5Cu₁Nb₃Si_13.5B₉ type. The techniques of Mössbauer spectroscopy, conversion electron Mössbauer spectroscopy, X-ray diffraction and transmission electron microscopy have been employed to compare their corrosion rate, characterize corrosion products and inspect the structural changes of the nanocrystalline structure. It was found that the Si-containing FINEMET alloys are the most corrosion-resistant whereas worse corrosion properties were observed for molybdenum-containing Fe₇₆Mo₈Cu₁B₁₅ alloy. The corrosion product formed on the surface of NANOPERM-type alloys showed a needlelike morphology and a poor crystalline order and has been identified as lepidocrocite, γ-FeOOH.     

Nanocrystals magnetic contribution to FINEMET-type soft magnetic materials with Ge addition

Over the last years several works have been published in which magnetic and structural properties of soft magnetic nanocrystalline alloys were reported. Among these, there are a series of articles where the nanocrystals composition of FINEMET-type alloys with Ge addition was obtained by Mössbauer spectroscopy (MS) and X-ray diffraction (XRD). By considering a linear relationship between the magnetic moments of the nanocrystals and the composition of various elements in these crystallites, the magnetic moment of the nanocrystals was calculated. This paper reviews results obtained by different authors since 1980 and they are compared with ours. In turn, we revised some elements not previously considered for the calculus of the nanocrystals composition that allowed us to obtain the magnetic moment of the crystallites in the alloy. In particular, we analyzed FINEMET-type alloys with replacement of B for Ge: Fe_73.5Si_13.5Ge₂B₇Nb₃Cu₁ and Fe_73.5Si_13.5Ge₄B₅Nb₃Cu₁. The nanocrystalline structure was obtained by isothermal annealing of melt-spun ribbons at 823 K for 1 h. From MS and XRD we obtained the atomic composition of the nanocrystals in the magnetic material. The magnetic contribution of the nanocrystals to the alloy was calculated using a linear model and the results were compared with experimental measurements of the samples.     

Structural characterization and magnetoimpedance effect in amorphous and nanocrystalline AlGe-substituted FeSiBNbCu ribbons

Two series of rapidly solidified FINEMET (Fe_73.5Si_13.5B₉Nb₃Cu₁) alloys with and without partial substitution of Al (1.5 at%)/Ge (1 at%) were prepared by melt-spinning technique. The nanocrystallization process was carried out by the heat treatment of the as-spun ribbons at 560 °C for 1 h in a vacuum furnace. X-ray diffraction (XRD), transmission electron microscopy (TEM), differential scanning calorimeter (DSC), Mössbauer spectroscopy, and magnetoimpedance (MI) measurements were conducted on the as-quenched and heat-treated alloys to investigate their structural and magnetic properties. The average crystallite sizes obtained for the heat-treated samples were in the range of 10–12 nm as confirmed by our XRD and TEM data. The ultrasoft magnetic behavior observed for the Al/Ge-substituted nanocrystalline alloys was confirmed both by our magnetic data and magnetoimpedance ratio (MIR%) results. A twofold increase in the magnitude of the MIR% (99%) was observed for the Al/Ge-substituted nanocrystalline alloy against that of the pure FINEMET alloy (∼48%) measured at 5.5 MHz. This is believed to be related to the decrease of the magnetocrystalline anisotropy as well as magnetostriction decline due to the Al substitution for Fe atoms in this nanostructured alloy.     

介观结构对纳米晶软磁合金巨磁阻抗效应影响的理论分析

根据用原子力显微镜对Fe基纳米晶Fe_73.5Cu₁Nb₃Si_13.5B₉合金薄带的介观结构和巨磁阻抗效应的实验研究结果，提出了纳米晶软磁合金巨磁阻抗效应受其介观结构影响的理论模型.该模型成功地解释了低频对纳米晶软磁合金巨磁阻抗效应的影响，反映了现有“三明治”理论的主要特征，并弥补了它的不足；同时指出了纳米晶粒电导率σ、磁导率μ对合金巨磁阻抗效应有影响. 关键词： 铁基纳米晶合金 介观结构 巨磁阻抗效应 介观模型     

Fe73.5Cu1Nb3B9Si13.5非晶态合金的激波纳米晶化研究

实验表明,非晶态合金在激波影响下会转变为纳米晶.最近的实验进一步发现,Fe_73.5Cu₁Nb₃B₉Si_13.5非晶态合金中的Cu,Nb在激波晶化中的细化作用被抑制,且样品在这种转变之后作进一步的退火处理,其晶粒度变大而晶格常数变小.在激波晶化机理分析中提出了“激波流体晶化”构想. 关键词：     

激光辐照非晶Fe73.5Cu1Nb3Si13.5B 9微量晶化的穆斯堡尔谱研究

在激光功率为40—160W、扫描速度为10mm/s、激光光斑为20mm照射条件下,用CO ₂激 光辐照非晶Fe_73.5Cu₁Nb₃Si_13.5B_{9< /sub>产生微量晶化.利用透射穆斯堡尔谱 （TMS）技术分析了原始态和晶化后样品的超精细结构.确定了穆斯堡尔谱的基本参数——化 学位移(IS)、四极分裂(QS)、内磁场(Hhf)随激光功率变化的规律.分析表明，CO2关键词： 激光辐照 微量晶化 73.5Cu1Nb3 Si13.5B9')" href="#">非晶Fe73.5Cu1Nb3 Si13.5B9 穆斯堡尔谱}     

Influence of the special features of the effective magnetic anisotropy on the temperature dependences of the magnetoimpedance of nanocrystalline Fe<Subscript>73.5</Subscript>Si<Subscript>16.5</Subscript>B<Subscript>6</Subscript>Nb<Subscript>3</Subscript>Cu<Subscript>1</Subscript> strips

The influence of the thermal treatment type on the temperature dependences of the magnetoimpedance of nanocrystalline Fe_73.5Si_16.5B₆Nb₃Cu₁ alloy strips is investigated. The main mechanisms determining the temperature behavior of the magnetoimpedance of strips with induced magnetic anisotropy having various special features are established. The prospects for application of the alloy strips nanocrystallized in the presence of a magnetic field as sensitive elements of temperature sensors and special magnetic field detectors are demonstrated.     

Recoilless fraction, structural, magnetic and thermal properties of Fe73.5Cu1Nb3Si13.5B9 alloy

Differential scanning calorimetry, X-ray diffraction and room temperature Mössbauer spectrum measurements of Fe_73.5Cu₁Nb₃Si_13.5B₉ (Finemet) alloy have been carried out in order to study its structural and magnetic properties as a function of annealing temperature. The DSC profile of as-quenched Finemet showed two exothermic peaks at 530 and 702 °C, corresponding to two crystallization processes. The Finemet alloy remains amorphous at 450 °C with one broad peak in XRD pattern and one broad sextet in Mössbauer spectrum. When the Finemet alloy was annealed at 550 °C, only well indexed body-center-cubic phase was detected. After being annealed at 650 and 750 °C, the XRD patterns showed the coexistence of α-Fe(Si) and Fe-B intermetallic phases with the increase in XRD peak intensities, indicating the growth of crystallites and the decomposition of Fe_73.5Cu₁Nb₃Si_13.5B₉ alloy at elevated temperatures. The Mössbauer spectra of annealed Finemet alloy could be fitted with 4 or 5 sextets and one doublet at higher annealing temperatures, revealing the appearance of different crystalline phases corresponding to the different Fe sites above the crystallization temperature. The appearance of the nanocrystalline phases at different annealing temperatures was further confirmed by the recoilless fraction measurements.     

Critical phenomena in FINEMET alloy

The Fe_73.5Cu₁Nb₃Si_13.5B₉ FINEMET alloy has been prepared by the rapid solidification technique. The critical behaviour of this alloy in the amorphous as well as in its nanocrystalline states has been studied near their respective Curie temperatures. From the values of the critical exponents one can conclude that the alloy behaves like a 3D Heisenberg ferromagnet in the amorphous and nanocrystalline states. But there exists a slight increase in the value of β for the alloy annealed at 823 K (the nanocrystalline state) as observed in most of the amorphous alloys.     

Study of local environment of Cu atoms in Fe73.5Cu1Nb3Si13.5B9 alloy with different annealing temperature

The local environment of Cu atoms in Fe73.5Cu1Nb3Si13.5B9 alloy was investigated by extended X-ray absorption fine structure(EXAFS).Cu clusters began to order when the annealing temperature was around 733 K from the results of the Fourier transform curves.The fitting results showed that the first shell of the near fcc(face-centered cubic)Cu clusters only contained Cu atoms.The coordination number increased with the annealing temperature.Subsequently,the occupancy rate increased from 33.3%(annealed at 733 K)to 100% (annealed at 853 K).This local structural change of Cu atoms could probably affect the distribution of the bcc(body-centered cubic)α-Fe in Fe73.5Cu1Nb3Si13.5B9 alloy.     

Influence of structurization of amorphous Fe73.5Si13.5B9Nb3Cu1 alloy on its spectral properties

The optical properties of Fe_73.5Si_13.5B₉Nb₃Cu₁ ferromagnetic alloy in the amorphous, nanocrystalline, and crystalline states have been investigated by optical ellipsometry in the spectral range of 0.22–18 μm. It is established that the crystallization of alloy during heat treatment leads to a significant change in its optical constants, as well as the frequency dependences of dielectric functions calculated based on these constants. The structural ordering is accompanied by a considerable increase in the intensity of the fundamental absorption band and an occurrence of its blue shift. Some characteristics of conduction electrons are determined, the numerical values of which also depend on the degree of atomic order.     

Structural and magnetic correlation of Finemet alloys with Ge addition

The correlation between saturation magnetization and the magnetic moment per Fe atom in the nanocrystalline state is studied for Finemet-type alloys. These studies were performed on nanocrystalline ribbons whose compositions were Fe_73.5Si_13.5−xGe_xNb₃B₉Cu₁ (x=8, 10 and 13.5 at%). We used a simple lineal model, X-ray diffraction and Mössbauer spectroscopy data to calculate the magnetic contribution of the nanocrystals and the results were contrasted with the measured saturation magnetization of the different alloys. The technique presented here provides a very simple and powerful tool to compute the magnetic contribution of the nanocrystalline phase to the alloy. This calculus could be used to determine the volume fraction of nanocrystalline and amorphous phases in the nanocrystallized alloy, without using a very sophisticated microscopy method.     

应力退火Fe基纳米晶薄带横向磁各向异性的介观结构研究

用原子力显微镜(AFM)观测了不同张应力退火的Fe基纳米晶(Fe_73.5Cu₁Nb₃Si_13.5B₉)薄带横断面的形貌，并结合X射线衍射(XRD)图谱对不同张应力退火的Fe基纳米晶薄带的介观结构进行分析；测量了不同张应力退火Fe基纳米晶薄带的纵向驱动巨磁阻抗(LDGMI)曲线及横向磁各向异性场；认为张应力退火Fe基纳米晶薄带感生横向磁各向异性场的介观结构机理，是由于外加张应力退火产生由非晶相包裹着的α-Fe(Si)纳米晶粒(包裹晶粒)的横向优势团聚. 关键词： 应力退火 介观结构 AFM 团聚     

Dynamic coercivity of Mo-doped FINEMETs

The structure and the dc magnetic behavior of FINEMET-type alloys doped with molybdenum have been recently reported. Most commercial applications of these materials are, however, not at dc but at high magnetizing frequencies. Therefore, we report a study of the frequency dependence of coercivity, H_c(f), in amorphous and nanocrystalline ribbons of composition Fe_73.5Si_13.5Nb_3−xMo_xB₉Cu₁ (x=0, 1.5 and 3) in the frequency range from 0.5 to 1.3 kHz. The nature of H_c(f) measurements revealed the influence of eddy currents in the magnetization of samples. The frequency dependence of coercivity did not vary with the molybdenum content in the amorphous samples. All the alloys exhibited a systematic improvement in the coercivity after nanocrystallization and it was found that this improvement was better as more Nb was replaced by Mo.