科学家首次绘制出3D磁畴图像

磁畴理论是用量子理论从微观上说明铁磁质的磁化机理。所谓磁畴,是指磁性材料内部的一个个小区域,每个区域内部包含大量原子,各个磁畴之间的交界面称为磁畴壁。同一磁畴内的原子磁矩都相同,但是不同磁畴的磁矩却各异,因此,磁畴磁场的方向就在磁畴壁这里发生了改变。科学界对磁畴理论的研究一直都停留在二维图像和材料表层的层面上,只能针对磁畴的横截面进行研究。     

KNbO_3 180°畴的第一性原理计算

利用第一性原理计算方法,考察铁电材料KNbO3的180°畴结构,并计算以K和Nb原子为对称中心的畴壁厚度、畴壁能及两种畴壁间移动的势垒高度.结果表明:该材料的畴壁厚度为1~2个晶胞常数;以K原子为对称中心的畴壁更稳定,其畴壁能为7.58 mJ/m2;以Nb为对称中心的畴壁不稳定,会逐渐变为以K为对称中心的畴壁,其畴壁能为15.16mJ/m2;畴壁移至最近邻晶格位置的势垒值为7.58mJ/m2.     

磁泡条畴头 Bloch 线产生的三维模拟

用改进的Ｄｕｆｏｒｔ－Ｆｒａｎｃｋｅｌ显示格式差分法求解条畴头畴壁运动时中心位置ｑ（ｚ，β，ｔ）和畴壁中心磁化矢量方位角（ｚ，β，ｔ）的耦合微分方程组．讨论了畴壁膨胀及杂散面内场对畴壁运动的作用以及脉冲驱动磁场Ｈｚ和薄膜材料阻尼因子对Ｂｌｏｃｈ线产生的影响．     

铁电体中电畴壁的经典行为

本文讨论铁电体中电畴壁在扰动力作用下的运动,指出在常力作用下畴壁有经典非牛顿粒子的行为.每一种铁电材料存在着与温度有关的本征频率,在周期性外电场作用下,畴壁作振动,但振幅不是常数,当外场频率接近本征频率时,振幅趋于稳定极大值,即发生共振,使电矩增加.     

面内场对枝状畴形成的IID畴壁中VBL链的影响

实验研究了面内场作用下枝状畴形成的第2类哑铃畴(IID)畴壁中垂直布洛赫线(VBL)链的解体过程.发现存在一个与材料参量有关的临界面内场范围[H(0)ip对应IID畴壁中垂直布洛赫ip,H(1)ip],其中H(0)线链保持稳定的最大临界面内场,H(1)ip对应IID畴壁中垂直布洛赫线链完全解体的最小临界面内场.此外,实验发现不同低直流偏场下产生的枝状畴在面内场作用下的软化过程相同,且在这个临界面内场范围内畴壁中的VBL是逐步丢失的.同时实验结果也证明了枝状畴畴壁中VBL是随机分布的.     

磁泡条畴头Bloch线产生的三维模拟

用改进的Ｄｕｆｏｒｔ－Ｆｒａｎｃｋｅｌ显示格式差分法求解条畴壁运动时中心位置ｑ（ｚ，β，ｔ）和畴壁中心磁化矢量方位角φ（ｚ，β，ｔ）的耦合微分方程组。讨论了畴壁膨胀及杂散面内场对畴壁运动的作用以及脉冲驱动磁场Ｈ和薄膜材料阻尼因子对Ｂｌｏｃｈ线产生的影响。     

钙钛矿型锰氧化物La0.7Sr0.3MnO3的磁谱研究

报导了钙钛矿型锰氧化物La0.7Sr0.3MnO3多晶体材料不同温度下磁谱的初步研究结果，平均粒径分别为45、66、105、140和1200nm的样品由溶胶－凝胶法制备，当平均粒径大于105nm时，样品的磁谱为典型的预豫型谱线，共振频率和准静态磁导率随温度降低而减少；随平均粒径增加，准记磁导率增大，而共振频率却减小，当平均粒径小于66nm时，观察不到类似的驰豫，实验结果显示，驰豫谱线主要是由于畴壁位移造成的，而畴壁位移的阻尼主要是与畴壁位移相联系的微观涡流效应。     

微观磁化理論(綜合評述)

引言在研究磁化理论时,人们可以从三个不同观点出发: 第一种是宏观的观点,即以B,H等概念为基础,研究磁化—磁滞曲线,磁导率等等。第二种观点是磁畴理论的观点,即从自发磁化Is,磁畴,畴壁与畴壁能,可逆与不可逆的畴壁位移和畴转等概念来研究问题。Landau-Liftshitz的磁畴理论采用了畴壁这一模型。在畴壁内Is随位置而连续地转变其方向。这种观点深入到畴壁内部,但     

PZT在机电疲劳作用下的微裂纹和畸变

通过对PZT铁电陶瓷试样在交变力四点弯、交变电场及机电耦合疲劳作用前后的微裂纹和电畴的观察研究发现：电畴畴壁垂直于硬度痕边界排列;裂纹附近畴壁趋于转向与裂纹平行的方向;极化试样中的微裂纹萌生和扩展显示出强烈的各向异性。另外,还试图解释实验实验观察到的在外加极化电场方向平行的初始试样表面内存在大量微观畴带的现象。     

温度对第二类哑铃畴畴壁中VBL的影响

实验研究了非压缩状态下第二类哑铃畴（ⅡＤ）畴壁中垂直布洛赫线（ＶＢＬ）的温度稳定性，发现了与材料参量有关的两个重要温度（Ｔ）（ⅡＤ）与（Ｔ０）（ⅡＤ）当温度达到（Ｔ　）（ⅡＤ）时，ⅡＤ畴壁中的ＶＢＬ开始丢失；当温度达到（Ｔ０）（ⅡＤ）时，所有ⅡＤ畴壁中的ＶＢＬ链全部解体。在（Ｔ　　）（ⅡＤ）与（Ｔ０）（ⅡＤ）之间，温度越高，ⅡＤ畴壁中丢失的ＶＢＬ数目越多。     

组合屏蔽层对电力变压器杂散损耗的影响

大容量单相电力变压器的箱体杂散损耗影响变压器效率和可靠性。通常采用箱体内壁敷设铁磁层的方法降低损耗,但铁磁叠片边界会使箱体局部磁场增强并产生局部过热。为此提出利用铁磁和非磁性导电层的不同组合屏蔽方法,并通过有限元仿真分析箱体和屏蔽层损耗,分析结果表明在优化屏蔽层厚度条件下纯导电层表面敷设一层铁磁材料,能有效降低总杂散损耗。     

铁磁材料磁力学声发射的频谱特征

研究了三种不同材料在不同应力下的磁力学声发射频谱特征,发现变化磁场对磁力学声发射波形的作用.通过对波形主频率及频带宽度的比较,发现材料内部应力状态与磁力学声发射的频谱有密切关系.     

Novel laminated multiferroic heterostructures for reconfigurable microwave devices

Voltage tuning of magnetism is fundamentally and technically important for fast, compact and ultra-low power electronic devices. Multiferroic heterostructures,simultaneously exhibiting distinct ferroelectric and ferromagnetic properties, have caught a lot of attentions because of the capability of controlling magnetism by a voltage via a strain-mediated magnetoelectric（ME） coupling. In these materials, a voltage-induced strain is involved to create an effective magnetic field and change ferromagnetic resonance frequency in the coupled ferromagnetic phases through magnetoelastic interactions. Therefore, the devices made of such materials are compact, ultra-fast and energy efficient,providing new functionalities for microwave components.This paper will review the recent progress of multiferroics and their applications in microwave devices from different aspects, including the creation of the novel laminated multiferroic heterostructures with a strong ME coupling, the realization of the multiferroics based on tunable microwave signal processors and the investigation of nonvolatile tuning of microwave properties using ferroelastic domain switching in multiferroic heterostructures. These tunable multiferroic heterostructures and devices offer great opportunities for realizing the next generation of tunable magnetic microwave components, ultra-low power electronics and spintronics.     

立方结构铁磁材料中畴壁阻力函数的研究

测定了镍、坡莫42、4％硅钢线(片)和铁、15号及45号优质碳素结构钢棒在匀速率增加外磁场下的微分磁化率——d磁场(dM/dH—H)关系曲线。结果表明,线(片)状试样与棒状试样具有不同的dM/dH—H关系曲线,这些曲线可用磁场速率α,以及A_(01),A_(02),A_1,A_2,B_1,C_1,C_2等参数拟合,每个参数均具有确定的物理意义。用磁畴壁运动理论得到了阻力函数的形式及其与材料性质、外场条件的关系。     

铁磁性导电薄板中磁损耗的理论计算

铁磁性导电薄板是实际中应用的铁磁性器件中最常见、最基本的物理模型.本文给出了在交变磁场的作用下的各向同性的铁磁性导电薄板中涡流效应产生的磁损耗的理论计算公式.结果表明减小铁磁性导电薄板的电导率和薄板厚度,是减小铁磁性导电薄板中由涡流效应引起的磁损耗功率的有效方法.     

Tunable quantum tunnelling of magnetic domain walls

Perhaps the most anticipated, yet experimentally elusive, macroscopic quantum phenomenon is spin tunnelling in a ferromagnet, which may be formulated in terms of domain wall tunnelling. One approach to identifying such a process is to focus on mesoscopic systems where the number of domain walls is finite and the motion of a single wall has measurable consequences. Research of this type includes magnetotransport measurements on thin ferromagnetic wires, and magnetization experiments on single particles, nanomagnet ensembles and rare-earth multilayers. A second method is to investigate macroscopic disordered ferromagnets, whose dynamics are dominated by domain wall motion, and search the associated relaxation-time distribution functions for the signature of quantum effects. But whereas the classical, thermal processes that operate in these experiments are easily regulated via temperature, the quantum processes have so far not been tunable, making difficult a definitive interpretation of the results in terms of tunnelling. Here we describe a disordered magnetic system for which it is possible to adjust the quantum tunnelling probabilities. For this material, we can model both the classical, thermally activated response at high temperatures and the athermal, tunnelling behaviour at low temperatures within a unified framework, where the domain wall is described as a particle with a fixed mass. We show that it is possible to tune the quantum tunnelling processes by adjusting the 'mass' of this particle with an external magnetic field.     

磁光材料中畴壁运动速度与外场间关系的研究

直接测量(BiTm)_3(FeGa)_5O_(12)薄膜中BLOCK壁的运动速度与外磁场变化率间的关系表明,畴壁运动速度随磁场变化率的增大关系与畴壁动力学关系相符.     

细密刻线多层膜的磁电阻特性和FMR谱

研究了细密到线（５００线／ｍｍ）的８１ＮｉＰｅ／Ｃｒ多层膜的磁电阻和铁磁共振（ＦＭＲ）谱，发现在这种多层膜中的畴模铁磁共振（ＤＭＦＭＲ）并非与条形畴相联系．证实了横向磁电阻响应中的Ｂａｒｋｈａｕｓｅｎ噪音（来源于畴壁不可逆的跳跃）消失了．     

Observation of coupled magnetic and electric domains

Ferroelectromagnets are an interesting group of compounds that complement purely (anti-)ferroelectric or (anti-)ferromagnetic materials--they display simultaneous electric and magnetic order. With this coexistence they supplement materials in which magnetization can be induced by an electric field and electrical polarization by a magnetic field, a property which is termed the magnetoelectric effect. Aside from its fundamental importance, the mutual control of electric and magnetic properties is of significant interest for applications in magnetic storage media and 'spintronics'. The coupled electric and magnetic ordering in ferroelectromagnets is accompanied by the formation of domains and domain walls. However, such a cross-correlation between magnetic and electric domains has so far not been observed. Here we report spatial maps of coupled antiferromagnetic and ferroelectric domains in YMnO3, obtained by imaging with optical second harmonic generation. The coupling originates from an interaction between magnetic and electric domain walls, which leads to a configuration that is dominated by the ferroelectromagnetic product of the order parameters.     

铁磁系统中介观畴壁的双波描述及量子涨落

 运用量子双波函数理论给出铁磁系统中介观畴壁的量子双波描述,在此基础上研究畴壁运动的坐标及动量的量子涨落,并对其进行讨论.