外加电场法制备LiNbO3周期畴的反转电流特性研究

采用外加电场法制备了LiNbO3单晶周期畴结构.在对不同尺寸周期畴的反转电流进行比较研究的基础上,提出了一种确定反转畴成核时间和纵向贯穿速率的方法.根据这一方法,得到在电场强度为25.1 kV/mm,脉冲宽度为50 ms的脉冲方波作用下,LiNbO3单晶反转畴的成核时间约为80 ns,纵向贯穿速率约为O.1667 m/s.     

掺镁铌酸锂亚微米结构畴反转的研究

研究了掺镁铌酸锂(MgO：LiNbO₃)的极化特性及其畴壁运动的性质,通过调节多个脉冲外加电场来控制畴壁的运动,在背向反转效应作用下,反转畴发生劈裂,制备出均匀的掺镁铌酸锂亚微米周期畴结构,并分析探讨了掺镁铌酸锂亚微米结构的成因及其反转机理. 关键词： 亚微米畴结构 掺镁铌酸锂 背向反转     

周期极化LiNbO3晶体中电极布置对反转畴扩张的影响

利用外加电场极化的方法,分别研究了三种不同方式布置的极化电极对C向切割LiNbO_{3< /sub>晶体极化反转畴扩张的影响.实验结果表明在相同极化条件下，当极化电极长度方向与六边 形反转畴一对边呈90°和0°角时，极化扩张速度分别为0.089μm/ms和0.011μm/ms.实验结果揭示，为了有效地控制极化占空比，在制备一维准相位匹配LiNbO3晶体时应 避免极化电极与六边形反转畴壁中一对边呈90°的情况. 关键词： 周期极化 极化扩张 准相位匹配}     

PZT铁电薄膜纳米尺度畴结构的扫描力显微术研究

利用扫描力显微术中压电响应模式原位研究了（111）择优取向的PZT60/40铁电薄膜的纳米尺度畴结构及其极化反转行为.铁电畴图像复杂的畴衬度与晶粒中的畴排列和晶粒的取向密切相关.直接观察到极化反转期间所形成的小至30nm宽的台阶结构，该台阶结构揭示了（111）取向的PZT60/40铁电薄膜在极化反转期间其畴成核与生长机理主要表现为铁电畴的纵向生长机理. 关键词： 畴结构 反转机理 PZT薄膜 扫描力显微术     

近化学计量比钽酸锂畴反转特性研究

采用助熔剂提拉法生长了非掺杂及掺镁近化学剂量比钽酸锂晶体.氢氟酸腐蚀晶片的金相显微镜观察结果显示,化学剂量比钽酸锂的畴结构为六边形.利用自行研制的极化设备对晶体进行极化实验,采用外加短脉冲极化电场,测定了近化学计量比钽酸锂单晶的畴反转特性,得到了完全反转的畴结构. 关键词： 近化学剂量比钽酸锂 畴结构 矫顽场 极化电流     

利用数字全息干涉术观察RuO2:LiNbO3晶体中畴反转的区域特性

利用马赫-曾德尔干涉光路和4f光学透镜系统，以部分畴反转的掺钌铌酸锂晶体(RuO₂:LiNbO₃)的透射光作为物光来记录全息图，并在数值再现过程对其进行频域滤波以实现物场波前信息的数值重建，检测出在一定电压作用下晶体内部折射率变化的二维分布.检测结果证实：晶体中发生畴反转的区域与发生电色效应的区域严格相符.数字全息干涉术非接触、无干扰、无破坏的优势在准实时监控、检测和分析铌酸锂晶体畴反转方面有很好的应用前景. 关键词： 畴反转 数字全息干涉术 电色效应     

掺镁铌酸锂晶体亚微米畴结构特性研究

基于畴背向反转效应，利用外加短脉冲极化电场，通过对脉冲宽度、脉冲间隔以及脉冲个数的有效控制，在掺5mol％镁的铌酸锂晶体上得到周期为1.7μm的均匀亚微米畴结构，其纵向深度为30—50μm.同时，使用脉冲宽度为100ms的宽脉冲信号得到了畴带宽度仅为0.5μm的非对称微畴结构对亚微米畴结构产生的微观机制和物理过程进行了初步探讨. 关键词： 背向反转效应 掺镁铌酸锂晶体 周期极化     

近化学计量比铌酸锂晶体周期极化畴反转特性研究

采用K2O作助熔剂直接拉晶法和气相输运平衡技术制备出了高质量近化学计量比铌酸锂晶体,研究了铌酸锂晶体中的[Li][Nb]比含量对其畴反转结构和极化电场的影响.实验结果表明:随着晶体中[Li][Nb]比的提高,畴极化反转电场呈明显下降趋势,使用近化学计量比铌酸锂晶体,在4.0±0.5kVmm大小极化电场条件下,成功地实现了1.0mm厚度的周期极化畴反转.并用铌酸锂晶体的Li空位缺陷模型对上述实验结果给出了合理的解释. 关键词： 近化学计量比铌酸锂晶体 周期极化 畴反转     

用于铁电体复杂畴结构模拟的布朗方程

铁电材料在室温下具有可以在外加电场作用下改变方向的自发极化,不同方向的极化在材料内部形成畴结构,会对其物理特性和实际应用具有显著影响.本文将最初用于微磁模拟的布朗方程引入铁电材料的大尺度模拟中,研究其中可能出现的重要畴结构.在以有效哈密顿量方法为基础推导出铁电材料中关于电偶极子的布朗方程后,以BaTiO₃,PbTiO₃块体和SrTiO₃/PbTiO₃/SrTiO₃夹心结构等钙钛矿铁电材料为研究对象,验证了布朗方程的有效性并讨论了其中的多种畴结构,如周期性条带状畴、涡旋型拓扑畴结构等,并与相关实验结果进行了对比分析.     

周期极化掺镁不同组分LiNbO3晶体的研究

利用气相平衡扩散法研制出掺镁不同组分的LiNbO₃晶体，并对其极化特性进行了研究.研究表明晶体的开关电场和自发极化不仅与晶体组分［Li］/［Nb］比有关而且与掺镁量有关，［Li］/［Nb］比为0.973掺入2mol% MgO的近化学比LiNbO₃晶体的开关电场仅为1.8kV/mm，是同成分晶体的1/12，且其极化结构的质量要远好于同成分LiNbO₃晶体和近化学比LiNbO₃晶体. 关键词： 气相平衡扩散 3晶体')" href="#">掺镁LiNbO₃晶体 周期极化     

Analysis of ferroelectric switching in sodium nitrite:poly(vinyl alcohol) nanocomposite films

The Fourier transform infrared (FTIR) spectra and switching current response in sodium nitrite:poly(vinyl alcohol) nanocomposite films have been studied as a function of composition of NaNO₂. The switching current data fitted well to infinite-grain model (IGM) in the region t<t _s and to finite-grain model (FGM) in the region t≥t _s . The microscopic parameters like the dimensionality, the domain wall velocity, and the nucleation rate have been evaluated which provide more physical insight of the switching phenomena in the composite films. The polarization current and nucleation rate are optimum in 50 wt.% composite film and have been discussed in terms of grain size and strain variations with the composition. The effect of applied field and pulse width variation on the switching behavior of 50 wt.% composition has also been studied. The exponential field dependence of the domain wall velocity and the nucleation rate indicate that nucleation mechanism is responsible for switching phenomena in the composite films. The writing pulse width affects significantly on the switching behavior of the composite films.     

Magnetization switching modes in nanopillar spin valve under the external field

The current-induced magnetic switching is studied in Co/Cu/Co nanopillar with an in-plane magnetization traversed under the perpendicular-to-plane external field.Magnetization switching is found to take place when the current density exceeds a threshold.By analyzing precessional trajectories,evolutions of domain walls and magnetization switching times under the perpendicular magnetic field,there are two different magnetization switching modes:nucleation and domain wall motion reversal;uniform magnetization ...     

The defects influence on domain wall propagation in bistable glass-coated microwires

We studied the domain wall (DW) dynamics of magnetically bistable amorphous glass-coated Fe₇₄B₁₃Si₁₁C₂ microwires. In according to our experimental results magnetic field dependences of DW velocity of studied microwires can be divided into two groups: with uniform or uniformly accelerated DW propagation along the microwire. Strong correlation between the type of the magnetic field dependence of domain wall velocity, v(H), and the distribution of the local nucleation fields has been observed.Moreover, we observed abrupt increasing of DW velocity (jump) on the magnetic field dependences of the domain wall velocity, v(H), for the both types of the v(H) dependences. At the same time usual linear increasing of the domain wall velocity with magnetic field persists below these jumps. It was found that the jump height correlates with the location of nucleation place of the new domain wall. We have measured local nucleation field distribution in all the microwires. From local nucleation field distribution we have obtained the DW nucleation locations and estimated the jump height     

Distinct ferroelectric domain switching dynamics in epitaxial BiFeO3 (001) capacitors depending on the bias polarity

Understanding ferroelectric domain switching dynamics at the nanoscale is a great of importance in the viewpoints of fundamental physics and technological applications. Here, we investigated the intriguing polarity-dependent switching dynamics of ferroelectric domains in epitaxial BiFeO₃ (001) capacitors using transient switching current measurement and piezoresponse force microscopy. We observed the distinct behavior of nucleation and domain wall motion depending on the polarity of external electric bias. When applying the negative bias to the top electrode, the sideways domain wall motion initiated by only few nuclei was dominant to polarization switching. However, when applying the positive bias, most of domains started to grow from the pre-existed pinned domains and their growth velocity was much smaller. We suggest that the observed two distinct domain switching behavior is ascribed to the interfacial defect layer.     

The role of nucleation field of media in heat-assisted magnetic probe recording

We characterize a method of heat-assisted magnetic probe recording on perpendicular media. Heating source is field emission current from a scanning tunneling microscope (STM) tip. Recording media are three kinds of magnetic films, Co/Pt, CoNi/Pt, and Co/Pd multilayers with different nucleation fields. Pulses with amplitude of 5 V were applied between the STM tip and the recording medium. Experiments show that magnetic marks with an average size of 180 nm were formed on both Co/Pt and CoNi/Pt films whose nucleation fields are greater than their saturation magnetization. No marks were observed on the Co/Pd film whose nucleation field is smaller than its saturation magnetization. A model is built to simulate the dynamic process of domain formation in probe-based magnetic recording system. Simulation results agree with experiments and it explains the effect of the nucleation field of medium in perpendicular recording.     

Temperature-electric field hysteresis loop of multicaloric effects in PbZr0.8Ti0.2O3 thin films

The Multicaloric effect in the PbZr_0.8Ti_0.2O₃ thin films is investigated with the application of sine wave electric field, dc electric field and stress using a phase field method combined with the thermodynamic analysis. The simulation results show that the adiabatic temperature change-electric field curve presents a shape of butterfly in the presence of the sine wave electric field. In order to detect the effect of the sine wave electric field, the multicaloric effect and the domain structures under the direct electric field and the sine wave electric field are compared. It is found that the domain switching behaviors are quite different under the different applied electric fields. And the negative multicaloric effect in the PbZr_0.8Ti_0.2O₃ thin film is attribute to the domain switching under the external field.     

Dynamics of ferroelectric domain formation in an atomic force microscope

The dynamics of ferroelectric domain formation in a non-homogeneous electric field of an atomic force microscope (AFM) tip are considered. Contributions of the apex and the conical part of the tip into the field are taken into account. It is supposed that this process passes through the same stages as the corresponding process in homogeneous external fields. However, the character of these stages may differ significantly. We consider all the stages of this process: formation of a nucleus, its growth, and the equilibrium domain parameters. Quantitative analysis is carried out for barium titanate. It is shown that the activation energy of nucleation strongly decreases with the applied voltage, and it is too small to limit the rate of the process even under low voltages. Dynamic equations for the time dependence of the domain length and radius are constructed and solved. Comparison of the calculated domain sizes with those observed in experiment is carried out. Calculated results obtained using different models for the field of the tip are compared.     

Domain wall creep in epitaxial ferroelectric Pb(Zr(0.2)Ti(0.08)O(3) thin films

Ferroelectric switching and nanoscale domain dynamics were investigated using atomic force microscopy on monocrystalline Pb(Zr(0.2)Ti(0.8))O(3) thin films. Measurements of domain size versus writing time reveal a two-step domain growth mechanism, in which initial nucleation is followed by radial domain wall motion perpendicular to the polarization direction. The electric field dependence of the domain wall velocity demonstrates that domain wall motion in ferroelectric thin films is a creep process, with the critical exponent mu close to 1. The dimensionality of the films suggests that disorder is at the origin of the observed creep behavior.