Magnetic Properties of Amorphous and Nanocrystalline Fe-Zr-B-Al Alloys

We have investigated the influence of aluminium substitution for iron on the magnetic properties of amorphous and nanocrystalline Fe_88-x Zr₇B₅Al _x alloys (x = 0, 1, 3, 5, 7 and 9 at.%). Thermomagnetic curves show an increase of Curie and crystallization temperature of amorphous phase with the increase of the content of aluminium in the alloy. The increase of aluminium content up to 3 at.% Al does not cause the decrease of a saturation magnetization in the as-quenched sample. In addition, magnetostriction of the annealed alloys has been studied. Also, the increase of aluminium content in the alloy causes an increase of the magnetostriction constant.     

Disordered spherical model

The most general expression of the free energy in the disordered spherical model is obtained. Based on this expression the following are shown, (a) The ferromagnetic order in the translationally invariant spherical model is unstable against an arbitrarily small random field ifd 4. (b) Straightforward generalization of the spherical model to the disordered case for a finite-range interaction has some rather unnatural properties: the phase transition in the model exists even in one dimension, and even in the case of ferromagnetic interaction it does not vanish as a homogeneous external field is switched on and spontaneous magnetization is zero forT _c . (c) For the ferromagnetic interaction, a modification of the disordered spherical model is proposed which does not have such properties and displays the behavior expected for the disordered ferromagnets. The paper also discusses the role of fluctuation (cluster) effects and the structure of the spontaneous magnetization field for the disordered spherical model. The results essentially rest upon the spectral properties of random self-adjoint operators obtained by the author earlier and in the present paper.     

静高压下Cu-Si块状纳米合金的制备与表征

 用压淬的方法，在6 GPa静高压下，以200 K/s的冷却速率冷却熔融状态的Cu₇₀Si₃₀合金，制备出块状Cu-Si纳米合金．X射线衍射和透射电子显微镜分析表明：该纳米合金由γ-Cu₅Si和一未知相组成，未知相为简单立方晶体，晶格常数α₀=0.853 5 nm，其热力学状态为亚稳态。并对静高压下块状纳米合金的形成机理进行了探讨。     

Magnetic Behavior of Nanocrystalline FeNbCrBCu Alloys at Elevated Temperatures

The magnetic behavior of nanocrystalline Fe_73.5Nb_4.5Cr₅B₁₆Cu₁ alloys is investigated in a series of specimens with different volume fractions of crystalline phase. It is shown that the Curie temperature of amorphous phase firstly decreases after structural relaxation in amorphous state and then rapidly increases during the first stages of crystallization. The strikingly different behavior of coercivity at elevated temperatures is observed for the samples with low and high volume fractions of nanocrystalline particles.     

Grain Boundaries in Magnetic Nanostructured Systems

The nanostructured systems are characterized by a density of grain boundaries which is higher than that of microcrystalline systems, giving rise to unusual properties. Both the structural nature and the thickness of grain boundaries which are dependent on the synthesis conditions, strongly influence the total magnetic properties. We report several examples based on metallic and insulating nanostructured systems to illustrate how the presence of grain boundaries can be experimentally evidenced, as well as their structure and magnetic behavior, and finally the significant role of grain boundaries on the magnetic properties.     

给定压力下纯铁材料的冲击相变与层裂特性研究

采用VISAR测量样品自由面速度剖面和回收样品观测分析联合技术,开展等厚对称碰撞实验,结合文献中的实验结果,研究了冲击加载压力大于纯铁材料冲击相变阈值约2~5 GPa和大于冲击相变阈值约10 GPa两种压力状态下纯铁材料的加卸载历程及各相区的变化,并从应力波相互作用的角度,指出了冲击加载压力略大于纯铁材料相变阈值约2 GPa时,等厚对称碰撞样品反常二次层裂与冲击相变及逆相变的关联机制。     

Phase transformation of ZrO2 nanoparticles produced from zircon

This article focuses on the phase transformation of zirconia (ZrO₂) nanoparticles produced from zircon using a bottom-up approach. The influence of mechanical milling and thermal annealing on crystalline phase transformation of ZrO₂ nanoparticles was explored. It was found that the iron oxide, as an inherent impurity present in ZrO₂ nanoparticles, produced from zircon stabilises the cubic phase after calcination at 600°C. The stabilised cubic phase of ZrO₂ nanoparticles was disappeared and transformed into partial tetragonal and monoclinic phases after mechanical milling. The phase transformation occurred on account of the crystal defect induced by high-energy mechanical milling. The destabilisation of cubic phase into monoclinic phase was observed after the thermal annealing of ZrO₂ nanoparticles at 1000°C. The phase transitions observed are correlated to the exclusion of iron oxide from the zirconia crystal structure.     

Microstructural evolution characterization of Fe–Nb–B ternary systems processed by ball milling

Fe–Nb–B alloys prepared by ball milling can undergo a complex microstructural evolution during milling. In order to overcome the limitations imposed by traditional X-ray bulk analysis, a comprehensive multi-technique approach was devised to systematically characterize samples with the required resolution. A combination of in situ FIB (focused ion beam) lift-out and high-resolution ATEM (analytical transmission electron microscopy) has allowed the characterization of the phase evolution during milling. In particular, boron inclusions, not detected by X-ray diffraction, have been found to remain undissolved in the Fe matrix.     

纳米尺度下Sm-Co合金体系中相组成与相稳定性的研究

建立了纳米晶合金相的热力学模型,可定量描述纳米尺度下合金体系中化合物相的热力学性质,并预测合金相的稳定性及其转变规律.利用该模型全面计算了纳米晶Sm-Co合金体系中各化合物相在不同晶粒尺寸下的摩尔吉布斯自由能随温度的变化关系,预测了纳米尺度下Sm-Co合金体系中各物相的相对稳定性及转变规律.模型预测结果示出,在室温附近,随着纳米晶粒尺寸的减小,某些纳米晶合金相的摩尔吉布斯自由能将由负值变为正值,预示着将向其他更稳定的纳米晶合金相转变,这是与传统粗晶材料中合金相的稳定性仅依赖于温度条件而完全不同的纳米晶合金 关键词： 纳米晶材料热力学 Sm-Co合金 相稳定性 相变     

部分相干X射线衍射相位成像与相位复原的模拟研究

借助于光学传递函数(OTF)概念，分析了微分相位成像过程和直接相位成像过程，讨论了通过图像处理进行相位复原的方法，得到了具有较高成像对比度和分辨率的实验参量区间，并利用数字方法模拟研究了相位成像的过程，对多种相位复原方法进行了比较。     

纳米晶304不锈钢高温氧化膜中Cr和Mn元素的XPS和UPS表征

利用X射线光电子能谱（XPS）和紫外光电子能谱（UPS）,对比研究了普通304不锈钢（CP-SS304）和深度轧制技术制备的块体纳米晶304不锈钢（BN-SS304）在900 ℃空气中氧化24 h后形成的高温氧化膜中Cr和Mn元素的结合能、原子百分比、价电子的相互作用和功函数,分析了BN-SS304表面电子结构的特征。结果表明：两种材料氧化膜中Cr元素以Cr3+和Cr0存在,Mn元素以Mn4+和Mn0存在,在不同溅射时间,BN-SS304氧化膜中Cr3+与（Cr3++Cr0）原子百分比和Mn4+与（Mn4++Mn0）原子百分比均低于CP-SS304氧化膜中的比值。两种材料氧化膜中价电子之间的相互作用主要有Mn—O,Cr—O,Mn0(3d和4s)和Cr0(3d和4s)。与CP-SS304相比,BN-SS304氧化膜表面价电子之间的相互作用强,其功函数比CP-SS304提高0.07 eV, BN-SS304的耐高温氧化性能增强。     

Magnetic Study of Nanocrystalline Ferrites and the Effect of Swift Heavy Ion Irradiation

100 MeV Si⁺⁷ irradiation induced modifications in the structural and magnetic properties of Mg_0.95Mn_0.05Fe₂O₄ nanoparticles have been studied by using X-ray diffraction, Mössbauer spectroscopy and a SQUID magnetometer. The X-ray diffraction patterns indicate the presence of single-phase cubic spinel structure of the samples. The particle size was estimated from the broadened (311) X-ray diffraction peak using the well-known Scherrer equation. The milling process reduced the average particle size to the nanometer range. After irradiation a slight increase in the particle size was observed. With the room temperature Mössbauer spectroscopy, superparamagnetic relaxation effects were observed in the pristine as well as in the irradiated samples. No appreciable changes were observed in the room temperature Mössbauer spectra after ion irradiation. Mössbauer spectroscopy performed on a 12 h milled pristine sample (6 nm) confirmed the transition to a magnetically ordered state for temperatures less than 140 K. All the samples showed well-defined magnetic ordering at 5 K, whereas, at room temperature they were in a superparamagnetic state. From the magnetization studies performed on the irradiated samples, it was concluded that the saturation magnetization was enhanced. This was explained on the basis of SHI irradiation induced modifications in surface states of the nanoparticles.     

Magnetic and Structural Properties of Electrodeposited Iron on Copper and Silver

Hyperfine Interactions - Electrodeposition of iron on copper or silver leads to the formation of bcc-iron or amorphous iron. Thermal annealing usually results in soluted iron (also γ-iron and...     

Y2O3:Eu3+纳米晶与体材料在高分辨光谱上的显著区别

报道了Y2O3：Eu^3 纳米晶与体材料在光谱上的显著区别。除了相同于Y2O3：Eu^3 体材料在580．6nm处的激发峰外,Y2O3：Eu^3 纳米晶在579．9nm处出现了一新的较宽激发线。并且,该激发线的寿命要稍短于580．6nm的激发线。579．9nm激发线被归因于靠近纳米晶表面的Eu^3 的发光。纳米晶中存在大量的表面缺陷。表面的晶体场因而发生退化,从而使得4f组态的电子能级发生移动。     

不同粒径纳米晶硫化锌的高压结构相变研究

 应用原位能量色散X射线散射和金刚石对顶砧技术,对纳米晶ZnS进行了高压结构相变研究。初始相为纤锌矿结构的10 nm和3 nm硫化锌分别在16.0 GPa和16.7 GPa时转变为岩盐矿结构,相变压力均高于纤锌矿结构的体材料硫化锌。该相变为一可逆的结构相变。应用大型科学计算软件Materials Studio（MS）计算了纳米晶ZnS的状态方程,根据Birch-Murnaghan方程拟合了纳米晶ZnS的零压体模量,得到的零压体模量高于相应体材料的零压体模量,表明纳米晶ZnS较难压缩。     

Attenuation of the Electric Potential and Field in Disordered Systems

We study the electric potential and field produced by disordered distributions of charge to see why clumps of charge do not produce large potentials or fields. The question is answered by evaluating the probability distribution of the electric potential and field in a totally disordered system that is overall electroneutral. An infinite system of point charges is called totally disordered if the locations of the points and the values of the charges are random. It is called electroneutral if the mean charge is zero. In one dimension, we show that the electric field is always small, of the order of the field of a single charge, and the spatial variations in potential are what can be produced by a single charge. In two and three dimensions, the electric field in similarly disordered electroneutral systems is usually small, with small variations. Interestingly, in two and three dimensional systems, the electric potential is usually very large, even though the electric field is not: large amounts of energy are needed to put together a typical disordered configuration of charges in two and three dimensions, but not in one dimension. If the system is locally electroneutral—as well as globally electroneutral—the potential is usually small in all dimensions. The properties considered here arise from the superposition of electric fields of quasi-static distributions of charge, as in non-metallic solids or ionic solutions. These properties are found in distributions of charge far from equilibrium.     

纯铁和铁基合金楔形样品中的冲击相变研究

 使用平面爆轰波起爆元件起爆TNT炸药,分别对DT2工业纯铁和HR2抗氢钢楔形样品进行了冲击加载实验。在回收样品中,DT2纯铁表现为宏观不规则破坏,而HR2钢仅在样品内部沿加载面约45°角和垂直方向出现了宏观裂纹。通过金相组织观察、显微硬度分布测量,结合数值计算,表明DT2纯铁样品在距加载面约2 mm范围内产生了不完全α-ε相变,在HR2钢中未发生相变。不完全相变可能是导致两种材料宏观破坏特征差异的因素。     

Investigation of Phase Separation in a Partially Miscible Polymer Blend by Rheology

The phase boundary and phase‐separation dynamics of a binary poly(styrene‐co‐maleic anhydride)/poly(methyl methacrylate) blend have been investigated by rheological measurements and light scattering. The phase diagram was experimentally established by rheology, in which the binodal line was obtained by dynamic temperature ramps and the spinodal temperatures were quantitatively estimated on the basis of the theory developed by Ajji et al. The phase‐separation dynamics from rheological viewpoints have been further investigated on the basis of the obtained phase diagram. Rheological measurements can sensitively detect the rather early stages of phase separation compared with light scattering techniques. It was found that the dynamic storage modulus initially increases over time and subsequently decreases during nucleation and growth; on the other hand, it always decreased over time during spinodal decomposition. Compared with light scattering techniques, rheological measurements were found to be relatively reliable for probing phase‐separation mechanisms.     

Geometric Phase in Fluctuating Magnetic Field

Geometric phase in a two-level atom with a fluctuating magnetic field is calculated by a nonunit vector ray in a complex projective Hilbert space, where the nonunit vector is a map connecting with density matrices of a quantum open system. We find that the Pancharatnam phase oscillates with evolving time. The Berry phase depends on the fluctuating parameter but it is proportional to the area spanned in the Bloch parameter space.     

Bulk and Surface Effects in X-Ray Magnetic Circular Dichroism of Iron Clusters

General trends in x-ray magnetic circular dichroism (XMCD) spectra of iron clusters of different sizes are theoretically investigated using the fully-relativistic spin-polarized multiple-scattering formalism. Purely geometrical effects of clustering and cluster-size effects are explored separately from effects of various scattering potentials and/or treatment of the surface barrier. We found that a high portion of non-bulk atoms makes the XMCD spectra of iron clusters to appear significantly different from bulk spectrum, even for quite large clusters. If the vacuum surrounding the cluster is taken into account, XMCD spectra of iron clusters change essentially (in comparison with clusters cut out of the bulk or with clusters embedded in a sea of free electrons).