Structure and magnetic properties of Nb-doped FeZrB soft magnetic alloys

Structure and magnetic properties of Nb-doped (FeZrB)_100−xNb_x alloy are investigated by X-ray diffraction (XRD), differential scanning calorimetry and vibrating sample magnetometer. The fully amorphous structure of the as-quenched ribbons is confirmed by the XRD pattern. With increasing Nb, the glass transition temperature and the onset crystallization temperature are increased, indicating increased stability of the amorphous structure. For x=1, the saturation magnetization of the ribbons is 125.7 emu/g and the optimized annealing temperature increases from 550 to 630 °C. The morphology of the crystallized phases is observed by scanning electron microscopy. The results show that nanocrystalline α-Fe grains are dispersed in the amorphous matrix.     

Mg-Ni-Nd非晶合金晶化温度与晶化驱动力的预测

通过对Buschow提出的预测二元非晶态合金晶化温度的“最小空位”模型进行扩展,并进一步结合Miedema理论得到了一种预测三元非晶态合金晶化温度和晶化驱动力的理论方法.利用该方法计算了(Mg_70.6Ni_29.4)_1-xNd_{x(x＝5,10,15)非晶态合金的晶化温度、晶化驱动力以及晶化焓.其中晶化温度和晶化焓的理论预测值与实验值的相对误差分别小于8%和7%.同时发现较高的晶化驱动力会降低 关键词： 非晶态合金 晶化温度 晶化驱动力}     

Nb添加对Cu-Zr非晶合金玻璃转变和晶化动力学的影响

采用铜模吸铸法制备出直径为2 mm的Cu_50.3Zr_49.7-xNb_x(x=0,2)大块非晶合金，利用示差扫描量热分析(DSC)研究了2at%Nb元素添加对Cu-Zr非晶合金玻璃转变动力学和晶化动力学的影响，发现含Nb合金具有较低的脆性指数，和较高的晶化激活能.这表明微量Nb的添加提高了该二元Cu基非晶合金过冷金属液相的热稳定性，从而有利于其非晶合金的形成. 关键词： Cu-Zr非晶合金 Nb添加 玻璃转变动力学 晶化动力学     

Effect of Cu addition on whisker formation in tin-rich solder alloys under thermal shock stress

This article focuses on the influence of thermal shocks and Cu addition on tin whiskers growth on the surface of tin-rich materials and alloys. The tests were carried out on real samples manufactured with classical PCB technology. Four Pb-free materials i.e. pure Sn, Sn99Cu1, Sn98Cu2 and Sn97Cu3 were tested from the point of view of susceptibility to whisker formation after thermal shocks. Results show that all tested materials were prone for whisker formation. Copper addition in coexistence with thermal shocks did not promote the growth of filament-like whiskers.     

纳米Cu颗粒等温晶化过程的分子动力学模拟研究

采用分子动力学方法和镶嵌原子势,模拟了500个Cu原子(简称Cu₅₀₀) 组成的纳米颗粒的等温晶化过程.利用修正的均方位移、键对分析技术和内在结构(IS) 等方法对该过程中的结构和动力学行为进行分析研究.结果显示:与块体金属不同的是, Cu₅₀₀纳米颗粒在某一温度保温时,其晶化时间并不是一个定值, 而是存在一个统计分布,并且保温温度越低其晶化时间的分布范围越广, 最长晶化时间越长.在低温晶化时, Cu₅₀₀经历了一系列中间构型的转变才达到晶态, 表现出多步晶化的特征.文章作者研究了颗粒的初始构型对晶化进程的影响, 发现颗粒的初始结构特征和能量状态对其随后的晶化过程有着重要的影响, 同一温度下,颗粒初始构型的IS能量越低其晶化时间越长,这一点在低温时尤其明显.     

Effects of minor Cu addition on glass-forming ability and magnetic properties of FePCBCu alloys with high saturation magnetization

The effects of minor addition of Cu on glass-forming ability (GFA), thermal stability and magnetic properties of (Fe_0.8P_0.09C_0.09B_0.02)_{100? x} Cu _x (x?=?0–1) alloys were investigated. The introduction of Cu slightly increases the GFA and efficiently improves the primary crystallization of α-Fe nanoparticles. The alloy with 0.3% Cu addition shows the best GFA and the fully glassy rods can be produced up to 2?mm in diameter. The saturation magnetization of the glassy sample with 0.7% Cu addition can be enhanced from 1.44 to 1.60?T after proper heat treatment due to the precipitation of α-Fe nanoparticles in the glassy matrix. The combination of large GFA and high saturation magnetization as well as low cost makes the FePCBCu alloys as a kind of promising soft magnetic materials for industrial applications.     

分子动力学模拟尺寸对纳米Cu颗粒等温晶化过程的影响

采用分子动力学方法和镶嵌原子势, 模拟了4000个Cu原子和13500个Cu原子(简称Cu₄₀₀₀和Cu₁₃₅₀₀)组成的纳米颗粒以及块体Cu的等温晶化过程. 通过对这些颗粒在晶化过程中结构和动力学行为的分析研究, 发现低温时, 不同尺寸的纳米Cu颗粒均出现多步晶化, 且晶化时间的分布曲线远比高温时范围大; 除了温度, 颗粒尺寸对晶化行为也有重要的影响, 尺寸越大, 晶化时间越长, 最终的晶化程度越高; 但是晶化时间随尺寸增大而增加的趋势不会一直持续, 发现存在一个临界尺寸r_c, 小于r_c时, 晶化时间随颗粒尺寸增大而增加, 大于r_c时,晶化时间随尺寸增大而减小.     

Effect of Ni and vacancy concentration on initial formation of Cu precipitate in Fe–Cu–Ni ternary alloys by molecular dynamics simulation

In the present work, the effects of Ni atoms and vacancy concentrations(0.1%, 0.5%, 1.0%) on the formation process of Cu solute clusters are investigated for Fe–1.24%Cu–0.62%Ni alloys by molecular dynamics(MD) simulations. The presence of Ni is beneficial to the nucleation of Cu precipitates and has little effect on coarsening rate in the later stage of aging. This result is caused by reducing the diffusion coefficient of Cu clusters and the dynamic migration of Ni atoms. Additionally, there are little effects of Ni on Cu precipitates as the vacancy concentration reaches up to 1.0%,thereby explaining the embrittlement for reactor pressure vessel(RPV) steel. As a result, the findings can hopefully provide the important information about the essential mechanism of Cu cluster formation and a better understanding of ageing phenomenon of RPV steel. Furthermore, these original results are analyzed with a simple model of Cu diffusion, which suggests that the same behavior could be observed in Cu-containing alloys.     

Effect of rare-earth elements on nanophase evolution, crystallization behaviour and mechanical properties in Al-Ni-R (R = La/Mischmetal) amorphous alloys

The crystallization behaviour and evolution of nanoparticles in amorphous Al-Ni-Mischmetal (Mm) and Al-Ni-La alloys during heat treatment have been studied. Rapidly solidified ribbons were obtained by induction melting and ejecting the melt onto a rotating Cu wheel in an Ar atmosphere. The crystallization behaviour of the melt-spun ribbons was investigated using differential scanning calorimetry and X-ray diffractometry (XRD). XRD studies confirmed that all the ribbons were fully amorphous. Al-Ni-Mm systems showed a three-stage crystallization process whereas Al-Ni-La system, in general, showed a two-stage crystallization process on annealing. Crystallization kinetics was analysed by Kissinger and Johnson-Mehl-Avrami approaches. In Al-Ni-La alloys, the crystallization pathways depend on the La concentration. Microhardness of all the ribbons was examined at different temperatures and correlated with the corresponding evolution of phases.     

Effect of the bath pH on the electrodeposition of nanocrystalline Pd–Co alloys and their magnetic properties

The effect of the bath pH on the electrodeposition of nanocrystalline Pd–Co alloys and on their magnetic properties was studied. The pH practically did not affect the alloy composition. Conversely, the pH showed a significant influence on the shape and size of crystallites. Two different crystallites morphology were observed depending on the bath pH. A crystallite size ranging from 18.2 to 30 nm was obtained from X-ray diffractometry (XRD) patterns using the Scherrer's method. Also from the XRD patterns the lattice strain percentage was calculated and correlated with the residual stress, which probably originated during the film electrodeposition on the substrate. Some alloy magnetic properties showed small variations. In contrast, high and unexpected coercivities were obtained reaching a maximum of 1.69 kOe at pH 5.5. The high coercivity values were attributed to the presence of residual stress at the film–substrate interface, which increased as the bath pH and crystallite size decrease, both of them contributing simultaneously to increase in coercivity.     

Effect of Al doping on the martensitic transition and magnetic entropy change in Ni-Mn-Sn alloys

Effect of Al doping on the martensitic transition and magnetic entropy change in Mn₅₀Ni₄₀Sn_10−xAl_x was investigated. The experimental results show that the martensitic transition temperatures increase with the increase of Al content due to cell contraction, while the martensitic transition temperature range decreases rapidly. Mn₅₀Ni₄₀Sn₈Al₂ alloy has the largest value of  (3.14 J/kg K) for the magnetic field changing from 0 to 10 kOe, which is nearly twice as large as that of Mn₅₀Ni₄₀Sn₁₀ alloy. It is demonstrated that a larger can be obtained due to the sharper magnetization change around martensitic transition.     

Effect of Fe addition on the crystallization behaviour and Curie temperature of CoCrSiB-based amorphous alloys

The crystallization behaviour and Curie temperature of melt-spun Co_{71? x} Fe _x Cr₇Si₈B₁₄ (x?=?0, 2, 3.2, 4, 6, 8 and 12?at.%) amorphous alloys have been studied. Differential scanning calorimetry (DSC) showed two stages of crystallization. The first stage of crystallization (T _X1) in the alloy with 6?at.%?Fe was the highest and it had the highest activation energy. X-ray diffraction studies revealed that the primary crystalline phase is hcp-(CoCr)₂Si for Fe-free alloy, whereas (CoFeCr)₂Si and (CoFeCr)₃Si phases were formed with the addition of Fe. hcp-Co was also formed along with these phases. The secondary crystalline phases were fcc-Co and various boron-rich phases. The Curie temperature of the alloys also changed with the addition of Fe to the system. Like the primary crystallization temperature, the Curie temperature of the alloys did not vary systematically with the Fe content. The addition of Fe to the Co-based system changes the nearest-neighbour interaction. This changes the exchange interaction between the transition metal elements. Due to the asymmetry in the Bethe–Slater curve, a systematic variation with Fe addition was not observed in the Curie temperature measurement.     

Grain oriented NiMnSn and NiMnIn Heusler alloys ribbons produced by melt spinning: Martensitic transformation and magnetic properties

We outline the microstructural, martensitic transformation and magnetic properties of Heusler alloys with starting compositions Ni₅₀Mn₃₇Sn₁₃, Ni₅₀Mn₃₆In₁₄, and Mn₅₀Ni₄₀In₁₀, produced by melt spinning. The ribbons were obtained in argon environment at a high wheel linear speed of 48 m s⁻¹ (typical dimensions: 1.2-2.0 mm in width, 4-12 mm in length, and 7-12 μm in thickness). EDS microanalysis showed that the resulting average elemental chemical composition is slightly shifted with respect to the starting one. Ribbons are fully crystalline and tend to show a highly ordered columnar-like microstructure with grains running through the entire ribbon thickness; the larger dimension of the grains is perpendicular to the ribbon plane. As-spun alloys were single-phase with ferromagnetic bcc L2₁ austenite as high-temperature parent phase. At low temperatures austenite transforms into a structurally modulated martensite with a lattice symmetry that depends on the system (7 M orthorhombic for Ni₅₀Mn₃₇Sn₁₃, 10 M monoclinic for Ni₅₀Mn₃₆In₁₄, and 14 M monoclinic for Mn₅₀Ni₄₀In₁₀). Magnetization isotherms measured in the temperature interval where martensite thermally transforms into austenite confirmed the occurrence of field-induced reverse martensitic transition in the alloys studied.     

Electronic structure and half-metallicity of the new Heusler alloys PtZrTiAl,PdZrTiAl and Pt0.5Pd0.5ZrTiAl

The electronic structure and magnetic properties of the PtZrTiAl, PdZrTiAl and Pt_0.5Pd_0.5ZrTiAl Heusler alloys were investigated using the full-potential linearized augmented plane wave (FPLAPW) within the generalized gradient approximation (GGA). For the PtZrTiAl, and PdZrTiAl alloys, the results showed that these Heusler alloys were stable in the Type I structure. The (Pt, Pd)ZrTiAl Heusler alloys are found to exhibit half-metallic ferromagnetism for both the Type I and Type II structure. The total magnetic moments of the PtZrTiAl and PdZrTiAl alloys were obtained to be 3 μ_B per formula unit, which are in agreement with the Slater-Pauling rule m_tot = (Nv ? 18). The half-metalliciy characteristic exists in the relatively wide ranges of 6.06–6.78 Å, and 6.13–6.73 Å for the PtZrTiAl and PdZrTiAl alloys, respectively. To complete the fundamental characteristics of these alloys, Pt_0.5Pd_0.5ZrTiAl is predicted to be a half-metallic ferromagnet with an energy gap of 0.90 eV in the minority spin and a complete spin polarization at the Fermi level. These new Heusler alloys may become ideal candidate material for future spintronic applications.     

Study of magnetic properties of ZnO nanoparticles codoped with Co and Cu

Here, we report on systematic studies of the magnetic properties of Co and Cu codoped ZnO nanoparticles prepared by sol–gel technique. The effect of hydrogenation and shape on the magnetic properties of Zn_0.93Co_0.05Cu_0.02O nanoparticles is presented. The Zn_0.93Co_0.05Cu_0.02O nanoparticles and well-aligned Zn_0.93Co_0.05Cu_0.02O nanorod array display ferromagnetic behavior at room temperature. Our results demonstrate the influence of shape and hydrogenation on the ferromagnetic properties of Zn_0.93Co_0.05Cu_0.02O nanoparticles at room temperature.     

Nb含量对FeSiBCuNb系铁基纳米晶合金结构和磁学性能的影响

为模拟Nb含量对FeSiBCuNb系铁基纳米晶合金结构和磁学性能的影响,采用Amorphous模块构建了Fe_88-xSi₉B₂CuNb_x(x=1,3,5,7)的硬球密剁模型,通过分子动力学方法进行弛豫,淬火以及退火处理,得到了Fe_88-xSi₉B₂CuNb_x(x=1,3,5,7)铁基纳米晶合金结构.基于第一性原理的计算方法,分析了不同Nb含量的铁基纳米晶合金的晶体结构和磁学性能.结果表明:随着Nb含量的增加,体系的晶格常数和体积都有所增大,导电性减小,磁矩不断减小,并且Fe的3d轨道是体系磁矩的主要贡献者,Nb元素对体系非晶化的形成有一定的作用.     

Effects of SnO2 addition on the microstructure and magnetic properties of NiZn ferrites

The microstructure and magnetic properties of SnO₂-doped NiZn ferrites prepared by a solid-state reaction method have been investigated. Due to its low melting point (∼1127 °C), moderate SnO₂ enhanced mass transfer and sintering by forming liquid phase, which accelerated the grain growth. However, excessive SnO₂ producing much of liquid phase retarded mass transfer and sintering, leading to a decrease in grain size. The diffraction intensity of the samples doped with SnO₂ addition was stronger than that of the sample without addition. The lattice constant initially decreased up to a content of 0.10 wt% and showed an increase at higher content up to 0.50 wt%. The initial permeability (μ_i) initially increased up to a content of 0.15 wt% and showed a decrease at higher content up to 0.50 wt%; however, losses (P_L) measured at 50 kHz and 150 mT changed contrarily. Both saturation induction (B_S) and Curie temperature (T_C) decreased gradually with increasing SnO₂. Finally, the sample doped with 0.10–0.15 wt% SnO₂ showed the higher permeability and lower losses.     

Synthesis and magnetic properties of multilayer Ni/Cu and NiFe/Cu nanowires

Highly ordered composite nanowires with multilayer Ni/Cu and NiFe/Cu have been fabricated by pulsed electrodeposition into nanoporous alumina membrane. The diameter of wires can be easily varied by pore size of alumina, ranging from 30 to 100 nm. The applied potential and the duration of each potential square pulse determine the thickness of the metal layers. The nanowires have been characterized by transmission electron microscopy (TEM), magnetic force microscopy (MFM), and vibrating sample magnetometer (VSM) measurements. The MFM images indicate that every ferromagnetic layer separated by Cu layer was present as single isolated domain-like magnet. This technique has potential use in the measurement and application of magnetic nanodevices.     

Influence of particle size and compaction pressure on the magnetic properties of iron-phenolic soft magnetic composites

This paper investigates the effect of particle size and compaction pressure on the magnetic properties of iron-phenolic soft magnetic composites (50 Hz-1000 kHz). The results showed that the optimum amount of phenolic resin to attain maximum permeability and minimum loss factor at 10 kHz is 0.7 wt% for samples containing iron powder with average particle size ∼150 μm compacted at 800 MPa. In accordance with this resin content, at high frequencies (>300 kHz), the sample with lower particle size ∼10 μm exhibits higher magnetic permeability, higher operating frequencies and lower imaginary part of permeability. With increase in the compaction pressure, specific resistivity decreases and imaginary and real parts of permeability increase at low frequencies.     

Formation of L10-FeNi hard magnetic material from FeNi-based amorphous alloys

L1₀-FeNi hard magnetic alloy with coercivity reaching 861 Oe was synthesized through annealing Fe₄₂Ni_41.3Si₈B₄P₄Cu_0.7 amorphous alloy, and the L1₀-FeNi formation mechanism has been studied. It is found the L1₀-FeNi in annealed samples at 400 ℃ mainly originated from the residual amorphous phase during the second stage of crystallization which could take place over 60 ℃ lower than the measured onset temperature of the second stage with a 5 ℃/min heating rate. Annealing at 400 ℃ after fully crystallization still caused a slight increase of coercivity, which was probably contributed by the limited transformation from other high temperature crystalline phases towards L1₀ phase, or the removal of B from L1₀ lattice and improvement of the ordering quality of L1₀ phase due to the reduced temperature from 520 ℃ to 400 ℃. The first stage of crystallization has hardly direct contribution to L1₀-FeNi formation. Ab initio simulations show that the addition of Si or Co in L1₀-FeNi has the effect of enhancing the thermal stability of L1₀ phase without seriously deteriorating its magnetic hardness. The non-monotonic feature of direction dependent coercivity in ribbon segments resulted from the combination of domain wall pinning and demagnetization effects. The approaches of synthesizing L1₀-FeNi magnets by adding Si or Co and decreasing the onset crystallization temperature have been discussed in detail.