强磁场下铑铁温度计的磁致电阻效应研究

以铑铁温度计为研究对象,研究了其在0-16 T磁场下、2-300 K温区内的磁致电阻效应.结果表明:铑铁温度计在0-16 T场强下,2-77 K温区内磁效应随场强的增强和温度的降低而明显升高,77-300 K温区内温度计受磁场的影响较小,其中在16 T、2 K处,以及16 T、300 K处的磁效应分别为70.94%和-...     

稀土掺杂锰氧化物的电致电阻效应

用固相烧结法制备Nd0.67Sr0.33MnOy（y=2.85）多晶样品。样品输运性质表现出自旋相关电致电阻特征。对含量低于化学计量y=3.0样品，当温度高于某一特征温度时，电阻变化符合线性欧姆定律；但低于这一特征温度时，电阻大小与负载电流或电压有关，I-V曲线偏离线性规律；在绝缘体．导体相转变点附近，样品电阻随负载电流或电压增大而迅速减小，表现出巨大电致电阻效应。这种自旋相关的电致电阻行为与氧含量和界面有很大关系。     

磁致伸缩液位变送器的原理与应用

磁致伸缩液位变送器是基于磁致伸缩原理和现代数字技术,能达到本质安全标准的新一代高精液位变送器,广泛应用于石油、化工、食品、制药、冶金等行业。本文主要分析了磁致伸缩液位变送器的工作原理,阐述了其主要技术参数和特点,分析了其常见的故障,并对磁致伸缩液位变送器的应用进行了探讨。     

超磁致伸缩材料ΔE效应理论建模与试验研究

为研究超磁致伸缩材料的ΔE效应,采用Jiles-Atherton模型和磁弹性效应相结合的方法,提出了一种考虑动态应力影响及系数变化的磁化模型。分别对磁场和应力作用下超磁致伸缩材料的磁场-磁化关系和应力-磁化关系进行建模,并根据胡克定律以及二次畴转模型计算出材料在应力和磁场综合作用下的总应变,得到不同外加磁场下材料的应变-应力环。通过对应变-应力曲线斜率的计算,得到超磁致伸缩材料在不同外加磁场下,弹性模量随应力变化规律。搭建了应力测试装置,对不同磁场作用下Terfenol-D的磁化-应力响应和应变-应力响应测试,试验结果与模型计算结果基本一致,结果表明,ΔE效应是磁场能量和应力各向异性平衡的结果,Terfenol-D最大弹性模量变化达到513%。研究成果为新型机电系统变刚度设计提供了理论基础和调控手段。     

超磁致伸缩驱动器设计准则的建立

在分析超磁致伸缩材料的工作特性、超磁致伸缩驱动器的基本结构与工作原理的基础上,给出了超磁致伸缩驱动器的设计准则．在所提出的设计准则指导下,开发了用于振动主动控制的超磁致伸缩驱动器,并对其主要特性参数进行了测量．实验结果表明,该驱动器的输出性能达到了设计要求。验证了该设计准则的有效性和实用性．     

铁电性、高温超导电性和庞磁电阻(CMR)效应的共性特征探讨

从结构和相变两个方面探讨了铁电性，高温超导电性和庞磁电阻（CMR）效应的共性，指出这类性质是集体电子行为，是由各种结构层次（晶体结构，电子结构及自旋结构）相互作用，相互耦合共同引起的。     

日本NIMS发现超磁致伸缩效应的机理

日本物质材料研究机构（NIMS）传感材料研究中心的任晓兵研究小组称,他们已搞清楚了“超磁致伸缩效应”的机理。所谓超磁致伸缩效应,即对某种强磁性材料施加磁场后,其尺寸会发生变化,而施加外力后会产生磁场。这一研究成果可促进低成本超磁致伸缩材料的开发。     

Fe—SiO2颗粒膜的磁和隧道磁电阻效应

采用射频共溅射方法制备了不同金属体积分数fv的Fe-SiO2颗粒膜,利用X射线衍射、透射电镜、Mossbauer效应和振动样品磁强计详细研究了薄膜的结构、磁性及磁电阻效应.结果表明fv为0.33时,得到磁电阻最大值-3.3%.Fe033(SiO2)067样品在室温下表现出超顺磁性,对该样品的变温Mossbauer谱研究表明颗粒的尺寸分布满足对数正态分布.探讨了TMP与Fe的依赖关系.     

计算磁致伸缩系数的优化算法

实验方法或有限元法可以获得磁致伸缩系数,但从避免试验操作不便和减少试验量考虑,提出一种计算磁致伸缩系数的优化算法,并研究了超磁致伸缩薄膜的变形问题.通过算例分析,结果发现,与有限元法相比,优化算法的计算结果与实验方法的结果吻合更好,具有较高的精确度.     

压缩应力下（Tb,Dy）Fe2磁致伸缩的研究

本文利用自制的磁致伸缩测量仪和“ｊｕｍｐ”效应测量仪研究了在一定压强了多晶（Ｔｂ、Ｄｙ）Ｆｅ２棒的磁致伸缩,发现加压时,在一定工艺条件下制作的（Ｔｂ、Ｄｙ）Ｆｅ２棒会有磁致伸缩的变化。卸载后经过热处理,磁致伸缩值在不加压时也会维持一个高值。     

Magnetic and structural phase transitions of MnBi under high magnetic fields

Abstract

High-field x-ray diffraction and magnetization measurements and differential thermal analysis (DTA) were carried out for polycrystalline MnBi with an NiAs-type hexagonal structure to investigate its magnetic and structural phase transitions. The lattice parameter a rapidly decreases below the spin reorientation temperature T_SR(=90 K) in a zero magnetic field. The parameter c decreases gradually with decreasing temperature and exhibits an anomaly in the vicinity of T_SR. By applying a magnetic field of 5 T, the parameter a increases by ～0.05% when T<T_SR and varies smoothly when 8≤T≤300 K. DTA data show that the magnetic phase transition temperature from the ferromagnetic state to the paramagnetic state increases linearly at a rate of 2 KT^?1 with increasing magnetic field up to 14 T.     

Magnetoresistance and electroresistance effects in Fe3O4 nanoparticle system

Nearly monodisperse spherical magnetite (Fe₃O₄) nanoparticles are prepared by colloidal chemistry route. Magnetic and electronic transport properties of the annealed pellets of these nanoparticles are reported. Effect of external magnetic and electric fields on the magnetic and transport properties of the material are studied as a function of temperature. We find that the highest resistance state of the ferromagnetic system occurs at a magnetic field which is approximately equal to its magnetic coercivity; this establishes the magnetoresistance (MR) in this system to be of the conventional tunnelling type MR as against the spin-valve type MR found more recently in some ferromagnetic oxide systems. The material also shows electroresistance (ER) property with its low-temperature resistance being strongly dependent on the excitation current that is used for the measurement. This ER effect is concluded to be intrinsic to the material and is attributed to the electric field-induced melting of the charge-order state in magnetite.     

Na0．75Co1-xErxO2的磁电阻

NaxCoO2具有奇异热电性质和电磁性质的强关联体系。为进一步探索材料中的电磁性质,制备出Na0．75Co1-xErxO2（0≤x≤0．10）多晶样品。对系统的电阻率、磁电阻和磁化率进行测量,结果显示,加磁场后系统的电阻减小,表明磁性离子对传导电子的散射作用;有效磁矩会随着Er的掺杂浓度增加迅速增大,3％的Er掺杂就能使有效磁矩几乎增大一倍;当系统的磁电阻达到15％,意味着Er的掺杂导致系统出现异常的电磁性质。     

Effects of magnetic fields on cracks in a soft ferromagnetic material

The 2D problem of a soft ferromagnetic solid with a finite crack under a uniform magnetic field has been studied based on the linear theory of Pao and Yeh. Especially, in this work, the Maxwell stresses induced by the applied magnetic field are taken into account in the boundary conditions not only along the crack surfaces, but also at infinity. Based on these boundary conditions, the related boundary-value problem is solved by using Muskhelishvili’s complex variable method to obtain the complex potentials. Thus, it is found that the obtained complex potentials are constant, which indicates that both magnetic fields and stress are uniform in the solid. This implies that if only a pure magnetic field is applied, it has no effects on a crack in a soft ferromagnetic solid. To confirm this result, the same boundary-value problem is solved by the integral transform technique, which shows the same finding as that by using the complex variable method. This outcome is consistent with available experimental data but different to previously published theoretical results.     

电场磁场对电流变液体减振器性能影响的研究

由于电流变液和磁流变液具有良好的可控性能和力学性能而在工程上具有广阔的应用前景.本文将其用于环形间隙通道外置的双缸电流变液体减振器.同时,对电流变液减振器在同时外加电场和垂直磁场作用下阻尼力的变化进行了理论研究和台架实验研究.结果表明,在外加电场和垂直磁场作用下,电流变效应得到加强,改善了减振器的示功特性.     

氧化镁磁隧道结磁电阻效应的研究进展

概述了近年来关于氧化镁磁隧道结磁电阻效应的最新研究进展,介绍了势垒层厚度、偏压、温度以及微结构等因素对磁电阻效应的影响.氧化镁磁隧道结的磁电阻效应与铁磁电极层和势垒层间的界面化学态与磁状态密切相关,势垒层厚度、偏压和温度等对磁电阻效应的影响关系表现出与传统氧化铝磁隧道结不同的变化特点.根据氧化镁磁隧道结磁电阻效应的研究状况,对其将来的发展进行了展望.     

Topology optimization in magnetic fields using the homogenization design method

To improve the performance of electric machinery, it is necessary to obtain the optimal topology of a structure in magnetic fields. The homogenization design method is applied to obtain the optimal topology. In the method, the change of inner hole size and rotational angle of unit cell determines the optimal material distribution in a design domain and this distribution defines an optimal topology. The objective function is defined as maximizing magnetic mean compliance (MMC). This is the same as maximizing magnetic vector potential and effective to improve the performance of electomagnet. The analysis and optimization is performed based on three‐dimensional hexahedral elements. This design method is applied to the H‐shaped electromagnet (H‐magnet). Copyright © 2000 John Wiley & Sons, Ltd.     

Effects of high magnetic fields on solidified structures of Mn-90.4 wt% Sb hypoeutectic alloy

Abstract

Mn-90.4 wt% Sb alloy specimens were solidified under both uniform magnetic field and magnetic field gradient conditions. The solidification behavior was examined to elucidate the effects of high magnetic fields on the solidified structure evolution of this hypoeutectic alloy. The macrostructures on the longitudinal section of the alloys were investigated by optical microscopy and x-ray diffraction (XRD). The volume fraction of primary MnSb phases and the interrod spacing of the eutectic were measured by metallographic analysis. It was found that the segregation of the primary MnSb particles at the certain regions of the specimens occurred under the influence of high magnetic field gradients. The MnSb phases obtained under magnetic fields were oriented with their (h0 l) planes along the direction of the magnetic field. Both the volume fraction of primary MnSb phases and the interrod spacing of the eutectic were decreased upon the application of the high magnetic fields.