Magnetic behavior and domain structure in as-quenched, annealed, and stress-annealed CoFeCrSiB ribbons

Combination of magneto-optical (MO) vector magnetometry and magneto-optical Kerr microscopy is used to investigate the surface magnetic properties of amorphous CoFeCrSiB ribbons. Strongly inhomogeneous magnetic behavior of ribbons in as-quenched state is improved by field-annealing and stress-annealing processes that induce weak uniaxial longitudinal and transverse anisotropy. It was shown that values of coercive and anisotropy field increase with increasing annealing temperature. Inclination of easy axis from the ribbon axis is estimated by comparing the measured surface hysteresis loops with the Stoner–Wohlfarth model, and is supported also by the Kerr microscopy. Method with the current flowing through the ribbon is proposed for magnetic domains observations.     

受拉扭弹性细杆超螺旋形态的定性分析

基于弹性杆的Kirchhoff模型讨论受拉扭弹性细杆的超螺旋形态.导出细长螺旋杆的等效抗弯和抗扭刚度.分析受拉扭弹性细杆的稳定性和分岔,且利用等效刚度概念将弹性杆的稳定性条件应用于对细长螺旋杆稳定性的判断.在扭矩不变条件下增加拉力至极限值时,直杆平衡状态失稳转为螺旋杆状态.继续增加拉力,直螺旋杆平衡状态失稳卷绕为超螺旋杆.从而对Thompson/Champney实验中受拉扭弹性细杆形成超螺旋形态的多次卷绕现象作出定性的理论解释. 关键词： 弹性细杆 Kirchhoff动力学比拟 等效刚度 超螺旋形态     

High-frequency properties of thin amorphous ribbons

Magnetic energy losses have been investigated in Co-based near-zero-magnetostriction amorphous ribbons from DC to 10 MHz. Attention has been devoted to the properties of field-annealed ribbons thinned down to 5.8 μm and their behavior at high frequencies. A rationale is provided for the frequency dependence of the magnetic losses over the investigated many-decade range through analysis of the loss components. Ribbons annealed under transverse field benefit by limited irreversible domain wall activity and correspondingly reduced hysteresis and excess losses. Based on the near-linear response of the material and the permeability–energy loss relationship, the separate contributions of domain wall displacements and rotations to the magnetization process and the related dissipation effects are singled out at all frequencies. Very thin amorphous ribbons are shown to display lower loss and higher permeability (i.e. higher Snoek's product) than Mn–Zn ferrites at all frequencies.     

Microstructure and magnetocaloric properties in melt-spun and high-pressure hydrogenated La0.5Pr0.5Fe11.4Si1.6 ribbons

The effects of wheel speeds and high-pressure hydrogen treatment on phase evolution, microstructure, and magnetocaloric properties in La_0.5Pr_0.5Fe_11.4Si_1.6 melt-spun ribbons are studied in this work. The results reveal that the increase of wheel speed is beneficial to the formation of cubic NaZn₁₃-type phase and the grain refinement. The optimized wheel speed for microstructural and magnetocaloric properties is 30 m/s. The largest entropy change of 18.1 J/kg·K at 190 K under a magnetic field change of 0 T-5 T is obtained in La_0.5Pr_0.5Fe_11.4Si_1.6 ribbons melt-spun at 30 m/s. After a high-pressure hydrogen treatment of 50 MPa, the Curie temperature of the ribbons prepared at 30 m/s is adjusted to about 314 K and the large -ΔS_M of 17.9 J/kg·K under a magnetic field change of 0 T-5 T is achieved at room temperature with almost none hysteresis loss. The small thermal and magnetic hysteresis and the large -ΔS_M make the La_0.5Pr_0.5Fe_11.4Si_1.6 hydride ribbons appropriate for magnetic refrigerant applications around room temperature.     

Magnetic and magneto-optical properties of CoFeCrSiB amorphous ribbons

In this paper we investigate the surface magnetic properties of as-quenched (AQ) CoFeCrBSi ribbons prepared by planar flow casting method with using magneto-optic Kerr effect (MOKE). Measured hysteresis loops in longitudinal and transversal configurations enable us to obtain the information of ribbons surface magnetic properties. Moreover, we suggest new magneto-optic method, which is based on measurements of magneto-optical effects depending on DC current flowing through the ribbon. Experimental data of AQ ribbons are then compared with the model, which describes the influence of incidence angle on magneto-optical angles.     

Textural analysis of a mesophase with banana shaped molecules

Observed under the polarizing microscope, the phase in the banana compound D14F3 [J.P. Bedel et al., Liq. Cryst. 27, 1411 (2000)] displays two types of textures of defects, namely (a): helical ribbons, that nucleate in large quantities when the samples are quenched from a sufficiently high temperature in the isotropic phase (b)- shapes with no helicity having the structure of developable domains much akin to those observed in columnar phases, either resulting from the annealing of the helical ribbons or nucleating under slow cooling processes. The existence of these two kinds of defects points toward the complex nature of the structure of the B7 phase, which is at the same time a columnar and a smectic phase. Our observations fit the model [M. Kleman, J. Phys. France 46, 1193 (1985)] according to which the geometry of a helical ribbon is that one of the central region of a screw dislocation with a giant Burgers vector, split into two helical disclination lines of strength k = 1/2 which bound the ribbon. Textures and defects, already partly documented, and growth features and annealing processes, not yet reported in the literature, are analyzed. We conclude that the helical ribbons and the developable domains with no helicity are textures of two different B7 states, namely a metastable state and the ground state respectively. Comparative textural analysis is performed for two other banana compounds exhibiting B2 phases.Received: 8 November 2003, Published online: 5 February 2004PACS: 61.30.Jf Defects in liquid crystals - 61.72.Bb Theories and models of crystal defects - 64.60.My Metastable phases     

铁基-铁镍基复合非晶态合金的磁性

用双喷嘴坩埚制备了非晶态合金Fe₇₈Si₉B₁₃和(FeNiCr)₇₈(SiB)₂₂的单层带材和复合带,并测量了两种合金的叠绕铁蕊和复合带铁蕊的热磁曲线和磁滞回线.对于两种合金的叠绕铁蕊,其磁滞回线呈峰腰型,类似于两种合金各自磁滞架线的平均值,但并不完全相同.对于复合带铁芯,其热磁曲线与两种合金热磁曲线的平均值基本重合,而磁滞回线不仅不再是蜂腰型,且非常扁平.叠绕铁芯和复合带铁芯磁滞回线的这种变化源于叠绕铁芯和复合带铁芯中的内应力.这种内应力产生的根本原因是两种材料热膨胀系数和磁致伸缩系数的差别. 关键词：     

Universal hysteresis scaling for incommensurate magnetic order in dysprosium

We study the scaling properties of magnetic minor hysteresis loops in a polycrystalline dysprosium metal, varying temperature and magnetic-field amplitudes. We observe irreversibility-related hysteresis loss in the helical antiferromagnetic phase, which is related with remanent flux density as a power law with the same scaling exponent of 1.25±0.05 as that in ferromagnetic materials. In contrast to hysteresis scalings in ferromagnets associated with 180° Bloch walls, the observed law is governed by spiral walls which separate helical domains with oppositely rotating spins.     

Entanglement complexity of lattice ribbons

We consider a discrete ribbon model for double-stranded polymers where the ribbon is constrained to lie in a three-dimensional lattice. The ribbon can be open or closed, and closed ribbons can be orientable or nonorientable. We prove some results about the asymptotic behavior of the numbers of ribbons withn plaquettes, and a theorem about the frequency of occurrence of certain patterns in these ribbons. We use this to derive results about the frequency of knots in closed ribbons, the linking of the boundary curves of orientable closed ribbons, and the twist and writhe of ribbons. We show that the centerline and boundary of a closed ribbon are both almost surely knotted in the infinite-n limit. For an orientable ribbon, the expectation of the absolute value of the linking number of the two boundary curves increases at least as fast as n, and similar results hold for the twist and writhe.     

Influence of Al and Ni on the magnetic properties of Finemet alloys

Crystallization behavior and soft magnetic properties of the FeSiBCuNbM (M=Al or Ni) Finemet alloys are investigated by X-ray diffraction, differential scanning calorimetry, hysteresis loop tracer, and vibrating sample magnetometry. The nanocrystalline alloys are prepared by annealing melt-spun amorphous ribbons at different temperatures. Results indicate that the partial substitution of Ni or Al for Nb results in the increase of saturation magnetic induction density (B_s) of the alloys. The alloys with Al or Ni show favorable combination of soft magnetic properties. The partial substitution of Ni for Nb enhances the B_s value, while Al decreases coercivity. The mechanism underlining the magnetic behavior is discussed.     

外场作用下铁电/铁磁双层膜的极化磁化性质

建立了铁电/铁磁双层膜模型,铁电层的电矩用连续标量描述,而铁磁层的自旋应用经典矢量描述.利用蒙特卡罗方法模拟了体系的热力学性质和极化、磁化行为.给出了零场下体系的内能、比热、极化和磁化随温度变化的关系,并分别研究了体系在外磁场和外电场下的极化和磁化行为.模拟结果表明,双层膜体系的内能、比热、极化和磁化性质因层间耦合系数的不同而明显不同,当界面耦合较弱时,双层膜表现出各自的热力学性质,当层间耦合增强到一定程度时,双层膜耦合为一个整体,表现出统一的热力学性质.该双层膜在外场中形成电滞回线和磁滞回线,并表现出偏置特性,界面耦合强度和温度影响滞后回线和偏置现象.     

A novel method determining longitudinally induced magnetic anisotropy in amorphous and nanocrystalline soft materials

In ferromagnetic amorphous and nanocrystalline soft magnetic alloys the induced magnetic anisotropy plays a fundamental role in the hysteresis behavior but, due to the elongated shape, it can be measured only if K_U is perpendicular to the sample long axis. In order to measure the longitudinal induced anisotropy, an original method derived from known thin layers measurement techniques was used. Hysteresis loops shifted by perpendicular bias field were recorded for this purpose. Direct measurement of the longitudinal induced anisotropy in amorphous and nanocrystalline ribbons or wire without needing sample preparation is reported for the first time. Evidence of self-induced anisotropy is brought in a Fe–Co-based nanocrystalline alloy.     

Experimental study of the motion of liquid droplets in a capillary under vibration

Results of an experimental study of the motion of small droplets in a capillary are discussed. The translational velocity of small droplets is studied as a function of the level and frequency of vibration acting together with a static force on the droplet—capillary system. The results are presented in the form of a set of curves, which reveal the nonlinear mechanical features of the system under consideration. The experiments confirm the previously developed theoretical model [7] based on the hysteresis dependence of the surface tension forces on the velocity of the meniscus motion.     

快淬Nd3.6Pr5.4Fe83Co3B5薄带的反磁化行为和磁黏滞性

用电弧熔炼法制备了Nd_3.6Pr_5.4Fe₈₃Co₃B₅合金铸锭,然后利用熔旋快淬法在铜辊转速V=20m/s下制备了Nd_3.6Pr_5.4Fe₈₃Co₃B₅薄带.快淬带主要由软磁相α-Fe和Nd₂Fe₁₄B型的硬磁相组成.采用直流退磁剩磁曲线方法分析了样品在反磁化过程中的可逆与不可逆磁化部分,并研究了软磁相和硬磁相的反磁化行为,得到样品的不可逆磁化形核场H_no约为440kA/m.同时研究了样品的磁黏滞性,结果表明由于软磁相的存在使得热激活体积较大. 关键词：     

空气域中铁磁流体动态控制研究

根据铁磁流体磁化后会受到磁力,退磁后不存在任何磁滞的超顺磁性质,提出了铁磁流体的动态控制方法,对喷射在空气域中的铁磁流体液柱直接添加电磁场实现其动态偏转驱动。在修正后的纳维-斯托克斯(N-S) 控制方程中加入表面张力、重力及磁力,并结合磁感应方程,建立了铁磁流体动力学(FHD)模型。利用二次开发的Fluent流体仿真软件建立了铁磁流体在空气域中喷射的流体体积函数(VOF)多相流模型,仿真了在不同磁场强度下铁磁流体的液相分布及分散状况,分析了磁性对其动力学行为的影响。结果表明,随着磁场强度和喷射距离的增大,铁磁流体沿磁场方向速度及偏移量增大,其发散情况逐渐明显。     

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Based on the superparamagnetism of the ferrofluid which can receive the magnetic force after magnetization by the magnetic field, and there is no magnetic hysteresis after demagnetization, this paper presents a dynamic control method of the ferrofluid. The electromagnetic field is directly added to ferroliquid-column in the air domain to achieve the dynamic deflection. The surface tension, gravity force and magnetic force are added to the modified N-S control equation, and the magnetic induction equation is combined. The ferrohydrodynamics (FHD) model is established. The model of volume of fluid (VOF) is presented to describe ferrofluid jetting in the air domain with the secondary development of fluent. The liquid phase distribution and dispersion of ferrofluid are simulated under different magnetic field intensity. The effect of magnetism on its dynamical behavior is analyzed. The results show that with the increase of magnetic field intensity and jet distance, the ferrofluid velocity along the magnetic field direction and the offset increase, and its dispersion is gradually obvious.     

Introducing a domain flexing function in the Jiles–Atherton hysteresis model

The Jiles-Atherton hysteresis model (J–A model) exhibits a certain unphysical behavior when magnetic excitation reaches or reverses from the extremity of the hysteresis loop. Introducing a domain flexing function, coherent with the magnetic excitation level, improves accuracy of the J–A hysteresis model and at the same time prevents its unphysical behavior. Moreover, applying this function also improves representation of inner (lower excitation level) hysteresis loops. Implementation of magnetic excitation dependence in the domain flexing function adds a valuable parameter to the J–A original model on the way towards its further optimization. In the proposed hysteresis model, genetic algorithms are used in parameters optimization.     

Pulsed laser deposition and annealing of Dy-Fe-B thin films on melt-spun Nd-Fe-B ribbons for improved magnetic performance

Pulsed laser deposition of 250-nm thick, amorphous Dy₂Fe₁₄B layers on 40-μm thick Nd₂Fe₁₄B melt-spun ribbons was conducted to improve coercivity and energy product. The coated ribbons were subsequently annealed by two methods: (1) furnace annealing in an inert-gas controlled quartz furnace using tantalum foil at 1173 K for 2 h; (2) laser annealing using a continuous wave CO₂ laser with power varying from 10 to 20 W for 0.2 s (estimated temperatures using a thermal model were 993-1528 K). X-ray diffraction was used to identify the microstructural phases and grain size. Magnetic hysteresis tests were conducted at 300 K using a SQUID magnetometer with a maximum field of 5.0 T. Results showed a 10% increase in coercivity and 30% increase in energy product in coated over uncoated samples that were furnace-annealed. However, the coated and laser-annealed samples exhibited soft magnetic behavior with almost zero coercivity. The incomplete crystallization of amorphous phase and precipitation of α-Fe during laser annealing are found to be responsible for the observation of poor magnetic performance.     

Unusual flow behavior of Fe-based soft magnetic amorphous ribbons under high temperature tensile loading

The viscous thermal flow behavior and mechanical property of [Fe_0.6Co_0.15B_0.2Si_0.05] _(100−x)Ta_x (x = 0, 1, 2, 3, 4, and 5) soft magnetic amorphous ribbons were studied. The characteristics of melt-spun amorphous ribbons were measured by using vibration sample magnetometer (VSM), nanoindentation, differential scanning calorimetry (DSC) and thermo-mechanical analysis (TMA) to study the effects of Ta content variation on the thermal stability, mechanical, and soft magnetic properties. We observed that the nanoindentation hardness, Young's modulus, and glass transition and crystallization temperatures were improved by the addition of Ta. Using dilatometry measurement, TMA, by heating at a constant rate under tension mode, we examined not only the glass transition and crystallization behaviors but also the possibility of coexistence of multiple amorphous phases.     

Magnetization and demagnetization behaviours of melt-spun Pr12Fe82B6 and Pr8Fe87B5 ribbons

Nanocrystalline Pr_{12}Fe_{82}B_6 and nanocomposite Pr_8Fe_{87}B_5 ribbons have been prepared using a melt spinning technique. Recoil loops have been measured at 20, 200 and 300K. Demagnetization curves are analysed by dividing it into reversible and irreversible portions. High recoil loop susceptibility at low applied field and large reversible change in the demagnetization curve have been found in Pr_8Fe_{87}B_5 ribbons, showing that the reversible behaviours in nanocomposite permanent magnets originate primarily from the magnetically soft phase. The hysteresis in recoil loops found in Pr_8Fe_{87}B_5 ribbons originates from the soft phase α-Fe that suffers a stress.