椭球体等形状介质的退极化因子

利用离散偶极子近似和电静态近似的方法研究了具有代表性的椭球体、圆柱体、立方体和其余5种形状介质粒子的吸收效率因子或内部电场,计算了外电场沿不同方向时粒子的退极化因子,阐明了得到任意形状粒子的退极化因子的简易方法.该计算结果可以加深学生对介质形状和退极化场大小关系的理解,并对介质的退极化因子的研究提供一定的参考.     

超导混合态椭球的交流磁化率

本文研究了处于混合态非均匀磁化的高温超导椭球在线性响应区的交流磁化率，给出了不同离心率的非均匀磁化椭球在直流磁场和小交流磁场中的交流磁化率的解析解析阐明了样品几何形状（退磁因子）对交流磁化率的影响文中研究了处于超地椭球的交流磁化率。     

基于多尺度理论的电各向异性介质椭球内电场

 基于电磁场的多尺度变换理论,将一个各向异性介质椭球重构为一个各向同性介质椭球,进一步得到了新椭球的形体参数。利用各向同性椭球电磁场与各向异性椭球电磁场的多尺度关系,得出了各向异性介质椭球内电场的解析表达式,对所得结果进行了验证。计算了椭球内电场方向与外电场方向的夹角,仿真结果表明：外电场的方向对椭球内电场的影响不大,介电常数张量对椭球内电场的方向和大小有较大的影响。     

一类变力 两种表现——关于"F=kV"类变力的讨论

在解决物理习题中,经常涉及两类变力:带电粒子垂直于匀强磁场方向运动时受到的洛伦兹力和闭合电路的部分导体在垂直切割磁感线时受到的安培力.这两种变力除了都是磁场力这一性质上的联系外,还具有一个重要的共同点,即力的大小都与速率成正比.     

普适条件下柱状样品的去磁因子、形状因子及磁化率校正公式

本文从无限长柱状介质的假定出发,推得了当NMR样品管与静磁场方向取任意夹角时样品的去磁因子,形状因子和磁化率校正公式,得到了在魔角条件下可消除溶液磁化率影响的结论与Garroway假定样品为椭球体介质所得结论类似。实验结果与本文的理论推导取得了很好的吻合。     

对《圆形有界磁场问题的分类及解析》文中一个解答的补充

《圆形有界磁场问题的分类及解析》[1]文中的例9,解答不够完整,这里给予补充和更正.题目及原解答如下.【题目】如图1所示,半径为R的圆筒形区域内,分布着磁感应强度为B,方向垂直纸面向里的匀强磁场.一带正电的微粒从圆筒壁上小孔A点沿半径方向射入磁场,且初速度方向垂直于磁场方向.若该微粒与筒壁碰撞时不损失电荷量,并能以大小相等的速度反向弹回,问初速度大小满足什么条件时,     

陶瓷超导体的磁化强度和临界电流密度

假定晶内临界电流密度 Jc 为常量(Bean 模型),由磁化强度定义直接计算了四种形状的晶粒的不可逆磁化强眨 M 与 Jc 的关系,得到了相应的 Jc(△M)中的几何因子修正量.对第二类超导体,退磁场和退磁因子在 Meissner 态和H_(c1)附近的混合态仍是重要的,在其余磁场中都可以忽略.对氧化物陶瓷超导块,由于弱连接,晶间磁场近似等于外场.讨论了块样中非超导部分对实验测量的磁化强度■及 Jc 估算的影响.     

垂直磁记录薄膜实施剩余磁化测量时退磁场的补偿

对于垂直磁记录薄膜，进行剩余磁化强度的测量时，必须补偿退磁场.提出一种新方法，在直流退磁剩磁和等温剩磁测量中采用有效反向磁场来直接补偿退磁场.从而可以正确地得出垂直磁记录薄膜的ΔM曲线并评价晶粒间的磁相互作用.还采用了三种方法来确定其中的关键参数——退磁因子.结果表明，c轴垂直取向的钡铁氧体薄膜中，晶粒间的磁相互作用是交换偶合型的；而Co-Cr-Ta薄膜中，晶粒间磁相互作用是静磁相互作用. 关键词： 退磁场补偿 直流退磁剩磁(DCD) 等温剩磁(IRM) ΔM曲线     

一道高考题与圆的不解之缘

题目:(2010年普通高校高考全国I卷第26题) 如图1所示,在0≤x≤3a区域内存在与xy平面垂直的匀强磁场,磁感应强度的大小为B.在t=0 时刻,一位于坐标原点的粒子源在xOy平面内发射出大量同种带电粒子,所有粒子的初速度大小相同,方向与y轴正方向夹角分布在0～180°范围内.已知沿y轴正方向发射的粒子在t=t0时刻刚好从磁场边界上P(3a,a)点离开磁场.     

退极化因子与形状因子

以球形或椭球形颗粒介质为例,从颗粒介质内外电势分布出发,得出了颗粒介质内部退极化场,从而进一步讨论了退极化因子和形状因子的关系.     

非均匀弱直流偏置磁场中CoFe-基非晶态合金丝的静磁化分布和退磁场分布

当前从事非晶态合金丝巨磁阻抗效应的理论研究均以忽略其内部退磁场为前提,该前提对于小尺寸非晶态合金丝不适用.本文提出一种用于计算Co Fe-基非晶态合金丝内部静磁化强度、退磁场分布的模型.该模型将非晶态合金丝内部划分成同轴、等宽、等厚、半径不同的相邻无交圆环,计算各圆环内磁化强度对场点r处退磁场冲激响应,得到冲激响应矩阵.利用该矩阵求解均匀/非均匀直流偏置磁场中非晶态合金丝内静磁化强度、退磁场分布.     

永磁体外部磁场的不均匀性研究

从永磁体的分子电流观点、退磁场、工艺等出发, 以矩形永磁体为例, 从理论上分析了影响永磁体外部磁场不均匀性的各种因素.研究结果表明, 永磁体外部磁场宏观不均匀性(好场区均匀度和面积相对大小) 和空间距离及永磁体的外形设计密切相关. 退磁场对永磁体外部磁场微观不均匀性有着复杂影响. 永磁体工艺如粉末颗粒、取向度、烧结凝固、机械加工等将影响永磁体外部磁场的不均匀性, 如磁化偏角、对称性、光滑性等. 关键词： 永磁体 外部磁场 不均匀性 退磁场     

The demagnetizing field on the surface of disc-shaped ferromagnetic samples

The local demagnetizing fields on the surface of flat cylindrical samples (disc) are measured by means of the free radical electron paramagnetic resonance for several thickness-to-diameter ratios from 0·01 to 0·15 and at two values of the external magnetic field (around 4 and 14 kOe). An empirical expression for the demagnetizing field intensity is found and anisotropy of the demagnetizing field is detected in the sample plane. The experimental results are compared with the conclusions of the theory of Joseph and Schlömann.We would like to thank to Mrs J.Smolíková for her help with the evaluation of the results and to Drs. R.Gemperle and V.Kamberský for many valuable suggestions to this problem.     

Influence of demagnetizing field on the permeability of soft magnetic composites

The influence of demagnetizing field on the effective permeability of magnetic composites has been investigated. A theoretical expression of the effective permeability has been obtained and discussed according to four typical composites with spheres, needles, flakes, and aligned prolate ellipsoidal particles. The results indicate that the demagnetizing field within the particles can reduce the effective permeability significantly. In order to increase the effective permeability, it is necessary to decrease the demagnetizing field within the particles. A linear relationship between effective permeability and volume fraction is also observed for composites filled with spherical particles at low volume fraction.     

消磁场对纳米铁磁线磁畴壁动力学行为的影响

为了实现基于磁畴壁运动的自旋电子学装置, 掌握磁畴壁动力学行为是重要争论之一.研究了在外磁场驱动下L-型纳米铁磁线磁畴壁的动力学行为. 通过微磁学模拟,在各种外磁场的驱动下考察了纳米铁磁线磁畴壁的动力学特性; 在较强外磁场的驱动下, 在不同厚度纳米线上考察了纳米线表面消磁场对磁畴壁动力学行为的影响. 为了进一步证实消磁场对磁畴壁动力学的影响, 在垂直于纳米线表面的外磁场辅助下分析了磁畴壁的动力学行为变化. 结果表明, 随着纳米线厚度和外驱动磁场强度的增加, 增强了纳米线表面的消磁场的形成, 使得磁畴壁内部自旋结构发生周期性变化, 导致磁畴壁在纳米线上传播时出现Walker崩溃现象. 在垂直于纳米线表面的外磁场辅助下, 发现辅助磁场可以调节消磁场的强度和方向. 这意味着利用辅助磁场可以有效地控制纳米铁磁线磁畴壁的动力学行为.     

Micromagnetic simulation for high field sensors with perpendicular magnetizations

In this paper, we present a micromagnetic design for high field sensors. The hard layer of the sensors is L1垂直磁化;强磁场传感器;微磁学模拟;高巨磁阻效应micromagnetic simulation, giant magnetoresistive, coercivity, demagnetizing fieldProject supported by the Nature Science Foundation of China (Grant No~10404019) and by the Science and Technology Committee of Shanghai (Grant No~05PJ14090).2006-09-232006-11-28In this paper, we present a micromagnetic design for high field sensors. The hard layer of the sensors is L1垂直磁化;强磁场传感器;微磁学模拟;高巨磁阻效应micromagnetic simulation, giant magnetoresistive, coercivity, demagnetizing fieldProject supported by the Nature Science Foundation of China (Grant No~10404019) and by the Science and Technology Committee of Shanghai (Grant No~05PJ14090).2006-09-232006-11-28In this paper, we present a micromagnetic design for high field sensors. The hard layer of the sensors is L10-FePt which is magnetized perpendicularly to film plane and the sense layer is NiFe which is magnetized in the film plane. The magnetization configurations of the hard and sense layers at different external magnetic fields have been simulated. In micromagnetic simulation, the sense field up to one tesla can be reached by using this sensor. We find that whether the sensor has a symmetric or an asymmetric field-sensing window is determined by the coercive field of the hard layer and the demagnetizing field of the sense layer.Corresponding author. E-mail： yaowen@mail.tongji.edu.cn/qk/85823A/200706/24631993.html7000, 7500, 7570P, 7540Mhttp://cpb.iphy.ac.cn/CN/10.1088/1009-1963/16/6/042https://cpb.iphy.ac.cn/CN/article/downloadArticleFile.do?attachType=PDF&id=1092012006-09-23In this paper, we present a micromagnetic design for high field sensors. The hard layer of the sensors is L10-FePt which is magnetized perpendicularly to film plane and the sense layer is NiFe which is magnetized in the film plane. The magnetization configurations of the hard and sense layers at different external magnetic fields have been simulated. In micromagnetic simulation, the sense field up to one tesla can be reached by using this sensor. We find that whether the sensor has a symmetric or an asymmetric field-sensing window is determined by the coercive field of the hard layer and the demagnetizing field of the sense layer.     

Magnetic domains perpendicular to the AC demagnetizing field in ordered Ni3Mn

Stripe domains with walls perpendicular to the AC demagnetizing field (PACD) are observed in atomically ordered, ferromagnetic NiMn with slightly more than 25 at.% Mn. Based on Lorentz microscopy and magnetic measurements. PACD is explained in terms of an inhomogeneity in the magnetic phase and coherent rotation of the magnetization in the domain.     

Influence of the demagnetizing factor on the magnetization of an ensemble of Stoner-Wohlfarth particles

The influence of the demagnetizing factor on the coercivity of a sample of oriented uniaxial Stoner-Wohlfarth particles is investigated in the approximation of a relaxation model with a self-consistent determination of the demagnetization field. The demagnetizing field is shown to change the particle magnetization reversal conditions and to reduce the blocking temperature and coercivity, for which, despite allowance for the demagnetizing field, the Neel-Brown relation holds. It is also shown that under the demagnetizing field, the internal magnetic field in which the particles are located is not stationary but varies with time concordantly with the time sweep of the temperature during magnetization in a constant external field after zero-field cooling (ZFC). Nonstationarity of the internal field in the ZFC regime causes the interval of transition temperatures of the ensemble particles from a blocked state to a state with equilibrium magnetization to increase.     

Experimental method for determining the total demagnetizing factor of thin amorphous ribbons

The basis of the method is the influence of the demagnetizing field on the maximum rate of magnetic flux change of the amorphous ribbon. The method allows to determine the demagnetizing factor of thin amorphous ribbons in a wide range of its values. With the proposed method the frequency dependence of the demagnetizing factor of amorphous ribbon with a helical magnetic anisotropy was found out.