Soft Magnetic Properties of Amorphous CoFeSiB Wire

Thermomagnetic analysis of the initial AC susceptibility of amorphous CoFeSiB wire shows strong stabilization of the domain structure. The initial susceptibility of the as-cast sample drastically decreases in the temperature range (100-250)°C due to directional reordering. A special form of the hysteresis loop is a consequence of large internal stresses introduced in the wire by the rapid melt quenching. It was shown that in the as-cast state the stabilization leads to the reduction of the number of Barkhausen jumps into one large Barkhausen jump at temperatures above 100°C. After stabilization at 150°C, the sample shows almost bistable behaviour even at room temperature.     

Barkhausen noise studies in amorphous materials at vanishing anisotropies

In this work, Barkhausen noise measurements are shown for the amorphous ribbons Metglas 2605TCA and Fe_73.5Cu₁Nb₃Si_18.5B₄ FINEMET material which is the amorphous precursor of the well-known nanocrystalline material, under different stress, annealing and magnetizing frequency conditions. These parameters were varied in search for different dynamical regimes of the complex system composed by the set of domain walls interacting with a reservoir of defects.     

CoFeSiB非晶丝弱磁场测量仪的研制

设计了以Co基非晶丝为敏感元件的传感器探头,多谐振荡励磁电路,信号处理电路,单片机显示电路,且对该磁场测量仪进行了标定。     

Distortions of the statistical distribution of Barkhausen noise measured by magneto-optical Kerr effect

In magneto-optical Kerr measurements of the Barkhausen noise, a magnetization jump ΔM due to a domain reversal produces a variation ΔI of the intensity of a laser beam reflected by the sample, which is the physical quantity actually measured. Due to the non-uniform beam intensity profile, the magnitude of ΔI depends both on ΔM and on its position on the laser spot. This could distort the statistical distribution p(ΔI) of the measured ΔI with respect to the true distribution p(ΔM) of the magnetization jumps ΔM. In this work the exact relationship between the two distributions is derived in a general form, which will be applied to some possible beam profiles. It will be shown that in most cases the usual Gaussian beam produces a negligible statistical distortion. Moreover, for small ΔI the noise of the experimental setup can also distort the statistical distribution p(ΔI), by erroneously rejecting small ΔI as noise. This effect has been calculated for white noise, and it will be shown that it is relatively small but not totally negligible as the measured ΔI approaches the detection limit.     

Exactly solvable model of avalanches dynamics for Barkhausen crackling noise

We review the present state of understanding of the Barkhausen effect in soft ferromagnetic materials. Barkhausen noise (BN) is generated by the discontinuous motion of magnetic domains as they interact with impurities and defects. BN is one of the many examples of crackling noise, arising in a variety of contexts with remarkably similar features, and occurring when a system responds in a jerky manner to a smooth external forcing. Among all crackling system, we focus on BN, where a complete and consistent picture emerges thanks to an exactly solvable model of avalanche dynamics, known as the ABBM model, which ultimately describes the system in terms of a Langevin equation for the velocity of the avalanche front. Despite its simplicity, the ABBM model is able to accurately reproduce the phenomenology observed in the experiments on a large class of magnetic materials, as long as universal properties are involved. To complete the picture and to understand the long-standing discrepancy between the ABBM theory and the experiments, which otherwise agree exceptionally well, consisting of the puzzling asymmetric shape of the noise pulses, microscopic details must be taken into account, namely the effects of eddy current retardation. These effects can be incorporated in the model, and result, to a first-order approximation, in a negative effective mass associated with the wall. The progress made in understanding BN is potentially relevant for other crackling systems: on the one hand, the ABBM model turns out to be a paradigmatic model for the universal behaviour of avalanche dynamics; on the other hand, the microscopic explanation of the asymmetry in the noise pulses suggests that inertial effects may also be at the origin of pulses asymmetry observed in other crackling systems.     

Rashba效应对量子线中束缚磁极化子性质的影响

采用改进的线性组合算符和幺正变换相结合的方法研究了Rashba效应对抛物量子线中强耦合束缚磁极化子性质的影响.计算了抛物量子线中强耦合束缚磁极化子的有效质量和振动频率,对Rb Cl材料的数值计算结果表明:量子线中强耦合束缚磁极化子的振动频率随受限强度和回旋频率的增加而增大;有效质量与磁极化子的受限强度、回旋频率和电子面密度有关,在Rashba效应影响下有效质量随上述各量的变化曲线都发生了分裂.     

Influence of the distance between two voltage contacts on giant magneto-impedance of Co-based amorphous wires

The Co₇₅ Fe_4.2Si₈B₁₂Nb_0.8 amorphous wires of 30 μ m in diameter are produced by melt extraction and annealing at 450 oC for 20 min in vacuum with a longitudinal or transverse field of 40 kA/m. Distances between the two voltage contacts of 6, 5, 4 and 2 mm are obtained by moving the two voltage contacts towards the centre of the sample at the same time. Results indicate that magneto-impedance response is dependent on the distance significantly. As distance decreases from 6 to 2 mm, △Z/Z reduces from 609% to 95% and giant magneto-impedance (GMI) profiles change from two-peak to single-peak. Besides, field sensitivity improves from 0.47%/(A/m) to 0.76%/(A/m) when the single-peak GMI just appears. It is therefore concluded that actual measurements can be made comparable only by taking into account the influence of distance between two voltage contacts for a magneto-impedance measurement.     

Effect of hardness and composition gradients on Barkhausen emission in case hardened steel

The effect of gradients in hardness, structure and composition in the surface layers on magnetic Barkhausen noise (MBN) was investigated in two widely used low alloy steels. One material was case hardened by induction hardening. The other was case carburised. Similar hardness profiles were produced by the two treatments. It was found that the variation in structure and hardness through the case in the induction-hardened steel had a minor effect on the MBN profile. In contrast, the inhomogeneity in the case-carburised material showed up clearly. This took the form of a broadened or two-peak MBN profile. When the surface layer containing the case was removed by etching, the broadened profile was replaced by a profile with a single peak. It is concluded that the shape and position of the MBN profile is significantly affected when a gradient in microstructure is induced by a gradient in carbon content. On the other hand, a gradient in microstructure induced by heat treatment with a constant carbon level has much less affect on the MBN profile for the induction-hardened steel.     

Effect of anisotropic microstructure on magnetic Barkhausen noise in cold rolled low carbon steel

We have measured the orientation and depth dependence of the magnetic Barkhausen noise (MBN) in an industrial pipeline steel sheet. Thin samples were cut out from the sheet cross section at different depths, parallel and transverse to the rolling direction (rolling and transverse samples). The integrated MBN energy has shown no depth dependence for transverse samples. On the other hand, the rolling samples have shown larger MBN noise energy and strong depth dependence.The microstructure of the samples was studied by optical and electron microscopy, parameters related to the shape and the quantity of carbon precipitates and grains were extracted by image processing techniques. The strong depth and orientation dependence of the MBN have been explained by changes of the grain and precipitate microstructure.     

Magneto-optical study of domain wall dynamics and giant Barkhausen jump in magnetic microwires

Investigation of surface domain walls motion in Co-rich magnetic microwires has been performed in circular and axial magnetic fields. The dc axial magnetic field acceleration of the domain wall motion related to the influence of the axial field on the structure of the moving domain wall has been discovered. Pulsed axial magnetic field induced unidirectional motion of surface domain wall also has been found.     

压强对Zr_(67)Ni_(33)非晶合金结构和动力学性能的影响

采用分子动力学的方法模拟Zr_(67)Ni_(33)合金液体在不同压强下快速凝固过程,通过结构分析方法如对分布函数、配位数、Honeycutt-Andersen(HA)键型指数法,以及动力学参数如均方位移、自散射关联函数、非高斯参数研究压强对Zr_(67)Ni_(33)非晶合金局域原子结构和其过冷液体动力学性能的影响.研究结果表明:压强越大,Zr_(67)Ni_(33)非晶合金中Zr-Ni原子间的相互作用越强,体系结构有序性越强,过冷液体中动力学减慢和动力学不均匀现象越显著.     

Stability of magnetic domains in an amorphous metal wire

Dimensions and energy of domains in the core of an amorphous metal wire are estimated in the work. Influence of the external magnetic field strength and coercive force on the dimensions of a stable domain is investigated. It is demonstrated that the highest stability to an external magnetic field and the least energy have domains comprising cylinder and cone-shaped domain tops and domains with zigzag domain tops. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 83–91, January, 2009.     

基于缠结微结构的非晶态玻璃态高分子材料屈服行为的分子动力学研究

非晶态玻璃态高分子材料作为结构材料在工程领域应用广泛,其机械力学性能特别是屈服变形行为受到热处理、加载应变率和环境温度的影响.采用分子动力学模拟方法研究非晶态玻璃态高分子材料不同工况下的单轴拉伸变形,基于分子链缠结微结构的概念,阐明了非晶态玻璃态高分子材料屈服和应变软化过程的内在变形机制.结果表明,拓扑缠结具有较为稳定的空间结构,难以发生解缠,决定了非晶态高分子材料屈服后的软化平台.由相邻分子链的局部链段相互作用形成的次级缠结在一定外界条件下可发生破坏或重新生成,次级缠结微结构及其演化是非晶态高分子材料发生屈服及软化的内在物理原因.     

镶嵌在氢化氮化硅中纳米非晶硅粒子光吸收的模拟

采用量子限制效应模型对镶嵌有纳米非晶硅粒子的氢化氮化硅薄膜的光吸收进行了理论模拟,探讨了由吸收谱分析给出该结构薄膜光学参数的方法,并通过对不同氮含量样品的讨论给出了量子限制效应和纳米硅粒子表面的结构无序对薄膜光吸收特性的影响规律。分析结果表明,随氮含量的增加,薄膜有效光学带隙增大,该结果与薄膜中纳米硅粒子平均尺寸的减小引起的量子限制效应的增强相关,而小粒度纳米硅粒子比例增加所引入的较高微观结构无序度和较多缺陷将会导致薄膜低能吸收区吸收系数增加。     

微磁动力学的新进展

本文介绍微磁动力学领域的一个最新进展,我们的研究发现在磁场驱动下且保持畴结构不变地沿着纳米磁线运动的磁畴壁,其运动源于能量耗散,磁畴壁运动速度正比于能量耗散率。与此同时,我们根据能量守恒原则,给出了磁畴壁速度的一个合理定义,该定义适用于任意的磁畴壁结构。在此定义下,即使磁畴壁没有做刚性运动,我们也能得到磁畴壁运动的瞬时速度和平均速度。我们的结果不仅能重复低磁场下的沃克（Walker）解,还能反映出当磁场高于沃克极限（Walker limit）时速度{磁场的依赖关系,该结果跟数值模拟和实验数据都符合得很好。我们根据微磁动力学研究的这一新进展,最终澄清了一个事实即“磁畴壁质量”这个概念是错误的。     

Novel processing of Barkhausen noise signal for assessment of residual stress in surface ground components exhibiting poor magnetic response

The Barkhausen Noise Analysis (BNA) technique has been utilised to assess surface integrity of steels. But the BNA technique is not very successful in evaluating surface integrity of ground steels that exhibit poor micro-magnetic response. A new approach has been proposed for the processing of BN signal and two newly proposed parameters, namely ‘count’ and ‘event’, have been shown to correlate linearly with the residual stress upon grinding, with judicious choice of user defined ‘threshold’, even when the micro-magnetic response of the work material is poor. In the present study, residual stress induced upon conventional plunge surface grinding of hardened bearing steel has been investigated along with unhardened bearing steel for benchmarking. Moreover, similar correlation has been established, when primarily compressive stress is induced upon high speed grinding using cBN wheel with moderately deep cut suppressing the micro-magnetic response from the ground medium carbon steel as the work material.     

药芯焊丝TIG焊电弧特性的光谱分析

利用光谱诊断方法结合高速摄像研究所提出的药芯焊丝的填丝TIG焊接新工艺的电弧特性,借助高速摄像研究药芯焊丝TIG焊的熔滴过渡方式;通过对焊接电弧进行光谱采集点扫描,对采集的谱线进行元素标定,以药粉中活性元素K和Na作为追踪目标,统计得到电弧中药粉成分的分布范围;并利用Boltzmann图法计算TIG焊电弧的温度场分布,分析了熔滴过渡方式对电弧温度场分布的影响。研究结果表明,通过调整丝极间距,得到药芯焊丝TIG焊的三种典型的熔滴过渡方式：滴状过渡(2 mm)、渣柱过渡(5 mm)和搭桥过渡(7 mm)。药粉中的活性元素K和Na等集中分布在熔池上方的电弧空间,且其分布受丝极间距的影响,丝极间距越小其分布越靠近钨极,容易造成对钨极的污染。不填丝TIG焊的电弧温度分布呈钟罩形,等温线关于钨极轴线近似对称分布;与不填丝TIG焊相比,药芯焊丝TIG焊的电弧温度场受熔滴过渡的影响发生了不同程度的扭曲,滴状过渡的电弧温度场扭曲严重,焊接过程中飞溅较大;相比于滴状过渡,渣柱过渡和搭桥过渡的电弧温度场扭曲程度较小且焊接过程稳定,适合该TIG焊方法的使用。     

Polaronic Effects of an Exciton in a Cylindrical Quantum Wire

The effects of exciton-optical phonon interaction on the binding energy and the total and reduced effective masses of an exciton in a cylindrical quantum wire have been investigated. We adopt a perturbative-PLL [T.D. Lee, F. Low, and D. Pines, Phys. Rev. B90 (1953) 297] technique to construct an effective Hamiltonian and then use a variational solution to deal with the exciton-phonon system. The interactions of exciton with the longitudinal-optical phonon and the surface-optical phonon have been taken into consideration. The numerical calculations for GaAs show that the influences of phonon modes on the exciton in a quasi-one-dimensional quantum wire are considerable and should not be neglected. Moreover the numerical results for heavy- and light-hole exciton are obtained, which show that the polaronic effects on two types of excitons are very different but both depend heavily on the sizes of the wire.     

电沉积复合丝及其巨磁阻抗效应的研究

采用脉冲电沉积工艺在Cu丝上沉积Fe Ni合金镀层 ,成功地制备出巨磁阻抗效应 (GMI)复合丝材料 ,研究了复合丝的磁性能和巨磁阻抗效应 .复合丝外壳磁性镀层软磁性越好 ,巨磁阻抗效应越明显 ,制备的复合丝最高巨磁阻抗效应为 2 7.19% .研究了复合丝阻抗与巨磁阻抗比值GMI随外加磁场的变化 ,其变化曲线的形状受复合丝磁各向异性场的影响 .此外 ,还研究了复合丝巨磁阻抗效应与驱动交变电流频率的关系 ,复合丝Fe17Ni83 样品巨磁阻抗效应的临界频率为 30kHz(GMI为 9.95 % ) ,特征频率为 30 0kHz(GMI为 2 7.19% ) ,截止频率为 10MHz (GMI为 10 .36 % ) .如此低的临界频率和特征频率及较宽的频率段对于实际应用非常有利 .     

Wire network behavior of superconducting films with lower symmetrical mesoscopic hole arrays

Superconducting films with the same hole density but different geometric symmetry have been designed and fabricated. The R(H) curves show obvious periodic oscillations with several dips at fractional matching fields. It is found that the period of the oscillations in the low field is not necessary equal to that derived from the hole density, but consistent with that from the corresponding wire networks when the large disk-like film regions are regarded as nodes. The experimental results of R(H), T_c(H) and j_c(H) at fractional matching fields within the first oscillation also support the rationality of considering films with large-diametered hole arrays as wire networks. Our results demonstrate that the connectivity of superconducting films with large-diametered hole arrays plays a more important role in the oscillations of R(H) curves.