The Magnetic Properties of the Spin-1 Ising System with?the?Effect of the Transverse Crystal Field

Within the framework of the effective-field theory with a probability distribution technique which accounts for the self-spin correlations, we study the magnetic properties of the spin-1 Ising system with the transverse crystal field and the applied external magnetic field. The influence of the transverse crystal field on the phase diagrams, hysteresis loops and susceptibility is discussed in detail.     

Ferroelectricity in highly ordered arrays of ultra-thin-walled Pb(Zr,Ti)O3 nanotubes composed of nanometer-sized perovskite crystallites

We report the first unambiguous ferroelectric properties of ultra-thin-walled Pb(Zr,Ti)O 3 (PZT) nanotube arrays, each with 5 nm thick walls and outer diameters of 50 nm. Ferroelectric switching behavior with well-saturated hysteresis loops is observed in these ferroelectric PZT nanotubes with P r and E c values of about 1.5 microC cm (-2) and 86 kV cm (-1), respectively, for a maximum applied electric field of 400 kV cm (-1). These PZT nanotube arrays (10 (12) nanotubes cm (-2)) might provide a competitive approach toward the development of three-dimensional capacitors for the terabyte ferroelectric random access memory.     

Dependence of ferroelectric and magnetic properties on measuring temperatures for polycrystalline BiFeO(3) films

A multiferroic BiFeO(3) film was fabricated on a Pt/Ti/SiO(3)/Si(100) substrate by a chemical solution deposition (CSD) method, and this was followed by postdeposition annealing at 923 K for 10 min in air. X-ray diffraction analysis indicated the formation of the polycrystalline single phase of the BiFeO(3) film. A high remanent polarization of 89 microC/cm(2) was observed at 90 K together with a relatively low electric coercive field of 0.32 MV/cm, although the ferroelectric hysteresis loops could not be observed at room temperature due to a high leakage current density. The temperature dependence of the ferroelectric hysteresis loops indicated that these hysteresis loops lose their shape above 165 K, and the nominal remanent polarization drastically increased due to the leakage current. Magnetic measurements indicated that the saturation magnetization was less than 1 emu/cm(3) at room temperature and increased to approximately 2 emu/cm(3) at 100 K, although the spontaneous magnetization could not appear. The magnetization curves of polycrystalline BiFeO3 film were nonlinear at both temperatures, which is different with BiFeO3 single crystal.     

Effects of Biaxial Crystal Field on the Magnetic Properties on?a?Spin-1?Ising?System

Within the effective field theory (EFT) with a probability distribution technique that accounts for the self spin correlation functions, the magnetic properties such as the hysteresis loops, susceptibility and magnetization of a spin-1 Ising system with effects of a biaxial crystal field are studied. The effects of the biaxial crystal field on the magnetic properties are discussed and numerical calculations are performed and analyzed for the cases of the honeycomb lattice. A number of interesting phenomena such as the shape of the hysteresis loops and the susceptibility have been found.     

Dynamic Magnetic Hysteresis Behaviors in a Mixed Spin (3/2, 2) Bilayer System with Different Crystal-Field Interactions

Dynamic magnetic hysteresis (DMH) behaviors of the mixed spin-3/2 and spin-2 Ising bilayer system with different crystal-field interactions on a two-layer square lattice is studied by the use of dynamic mean field calculations based on the Glauber-type stochastic. The hysteresis loops are obtained for different reduced temperatures (T), magnetic field amplitudes (h), frequencies (w) and interlayer coupling constants (J ₃). Influences of the T, h, w and J ₃ on the DMH properties are investigated. We also study the temperature, frequency and interlayer coupling interaction dependence of the coercive field and remanent magnetization. We compare our results with some theoretical and experimental works and observe a quantitatively good agreement with some theoretical and experimental results.     

Influence of Composition and Pressure on the Electric Field-Induced Antiferroelectric to Ferroelectric Phase Transformation in Lanthanum Modified Lead Zirconate Titanate Ceramics

The electric field-induced phase transformation behavior in lanthanum-doped lead zirconate titanate ceramics was examined by polarization versus electrical field (P-E) measurements carried out from room temperature to 130degC and under hydrostatic pressures from 20 to 300 MPa. The samples with composition (Pb_1-xLa_x)(Zr_0.90Ti_0.10)_1-x/4O₃ [PLZT _x/90/10; x = 2,3,4 at%] were prepared by the standard solid-state reaction method. The analysis at room temperature under atmospheric pressure showed that the increase in the lanthanum content induces a transformation from the typical ferroelectric hysteresis, observed for PLZT 2,3/90/10, to double-hysteresis loops, typical of antiferroelectric phases, for PLZT 4/90/10 under a strong electric field. Hydrostatic pressure- induced and temperature-induced ferroelectric (FE) to antiferroelectric (AFE) phase transformations were examined. The measured hysteresis loops indicated that the FE-AFE phase transformation depends on both temperature and hydrostatic pressure for PLZT 3/90/10. This composition, which is in a ferroelectric state at room temperature under atmospheric pressure, can be transformed into the antiferroelectric phase by the application of a hydrostatic pressure of 100 MPa or by increasing the temperature to around 90degC. The PLZT 2/90/10 and 4/90/10 compositions displayed predominantly ferroelectric and antiferroelectric behavior, respectively, over the ranges of temperature and hydrostatic pressure examined in the present study.     

Dielectric and field-induced strain behaviour of (Pb1−xBax) ZrO3 ceramics

The effects of Ba2+ substitution on the dielectric properties and induced strain behaviour of the (Pb1–xBax) ZrO3 ceramics (0.05x0.3) have been investigated as a function of x. A new phase diagram of the (Pb1–xBax) ZrO3 system, indicating the field effect on the phase transition, is also presented. As the Ba2+ content increases, the Curie temperature decreases linearly, whereas maximum dielectric constant increases for up to 20 mol% Ba2+ addition, and then decreases with further Ba2+ addition. Based on the hysteresis loops, the temperature range of the ferroelectric phase as an intermediate phase between the antiferroelectric and paraelectric phases, increases with increasing electric field and Ba2+ content. The ferroelectric loops are induced at room temperature for the specimens containing above 10 mol% Ba2+ by applying an electric field up to 25 kV cm–1. However, for the 5 mol% Ba2+-substituted specimen, no ferroelectric loop is induced, even with applied fields up to 55 kV cm–1. The phase transition due to electric field and Ba2+ addition is also confirmed by the measurement of the field-induced longitudinal strain.     

Dielectric Properties and Hysteresis Loops of a Ferroelectric Nanoparticle System Described by the Transverse Ising Model

In this work, we use the effective field theory based on the probability distribution method to investigate the longitudinal and transverse polarizations, susceptibility, pyroelectric coefficient, and the hysteresis behavior of a ferroelectric cubic nanowire. The effects of the core–shell exchange interaction and the core–shell transverse fields on the longitudinal and transverse polarizations, the susceptibility, the pyroelectric coefficient, and the hysteresis loops of the system are examined. Some characteristic phenomena are found in the thermal variations, depending on the physical parameters in the shell and in the core.     

Monte Carlo Study of Long-Range Interactions of a Ferroelectric Bilayer with Antiferroelectric Interfacial Coupling

By the use of Monte Carlo simulation, we have studied the critical behavior of a ferroelectric bilayer with antiferroelectric interfacial coupling using the transverse spin- $\frac{1}{2}$ Ising model. We discuss the effects of long-range interactions for the internal energy, specific heat, free energy, dielectric susceptibility, and polarization. The dependence of the Curie temperature on the thickness of the bilayer, long-range interactions, and the transverse field was also investigated. It is assumed that the long-range interaction decays with the distance between the pseudo-spins as a power law.     

电场对(Ba0.97Ca0.03)(Ti0.82Zr0.18)O3无铅压电陶瓷铁电性的影响

采用溶胶-凝胶方法制备了(Ba0.97Ca0.03)(Ti0.82Zr0.18)O3无铅压电陶瓷。在电场1～8kV/cm下,频率为0.01～10Hz范围内,对其电滞回线进行了分析。实验结果表明(Ba0.97Ca0.03)(Ti0.82Zr0.18)O3陶瓷的电滞回线随电场值和频率的变化明显,在低电场下,随着频率的增加矫顽场(Ec)单调减小,在低频下剩余极化(Pr)增加;而在高电场下,随着频率的增加Ec单调增大,电滞回线达到饱和时,电滞回线随不同测试频率无明显变化。     

Zero-Temperature Study of a Tetrameric Spin-1/2 Chain in a Transverse Magnetic Field

We consider an alternating Heisenberg spin-1/2 antiferromagnetic–ferromagnetic chain with the space-modulated dominant antiferromagnetic exchange and anisotropic ferromagnetic coupling (tetrameric spin-1/2 chain). The zero-temperature effect of a symmetry breaking transverse magnetic field on the model is studied numerically. It is found that the anisotropy effect on the ferromagnetic coupling induces two new gapped phases. We identified their orderings as a kind of the stripe antiferromagnetic phase. As a result, the magnetic phase diagram of the tetrameric chain shows five gapped quantum phases, and the system is characterized by four critical fields which mark quantum phase transitions in the ground state of the system with the changing transverse magnetic field. We have also exploited the well-known bipartite entanglement (name as concurrence) and global entanglement tools to verify the occurrence of quantum phase transitions and the corresponding critical points.     

Effect of composition on rate dependence of ferroelastic/ferroelectric switching in perovskite ceramics

Abstract

The process of ferroelectric/ferroelastic switching is rate dependent as evidenced by the frequency dependence of the coercive field/stress in polarisation/strain–electric field/stress loops. The rate dependence of domain switching has been investigated in different compositions of ferroelectric/ferroelastic perovskites by studying their stress–strain hysteresis loops. Stress–strain loops were generated by applying a static compressive load and then superimposing cyclic compressive loads of different amplitudes and frequencies. The stress–strain loops were fitted using a Rayleigh type relationship, whose parameters characterise the intrinsic and extrinsic contributions to the strain. Using these parameters, the rate dependence of the extrinsic domain wall contribution was investigated.     

The Hysteresis Behavior of a Spin-1 Blume-Capel Nanoisland

The magnetic properties of a spin-1 Blume-Capel nanoisland are investigated by the use of the effective field theory based on the probability distribution technique. The influence of the random crystal field and the system parameters on the hysteresis behavior and on the magnetic properties of the nanoisland is examined. The results show a number of characteristic behaviors, such as the appearance of double, triple, quadruple, and even quintuple hysteresis loops for appropriate values of the system parameters.     

结构设计对铁电薄膜系统电滞回线的影响

为制备符合Si集成铁电器件要求的高质量Si基铁电薄膜，采用溶胶—凝胶(sol—gel)工艺，制备了MFM及MFS结构的铁电薄膜系统，研究了不同结构及不同衬底对铁电薄膜系统铁电性能及电滞回线的影响，并对这些差异产生的主要影响因素进行了分析，在此基础上，提出并制备了Ag／Pb(Zr0.52Ti0.48)O3／Bi4Ti3O12／p—Si多层结构，该结构铁电薄膜系统的铁电性能及电滞回线的对称性有明显改善，有望应用于Si集成铁电器件。     

Quantum oscillations and ferromagnetic hysteresis observed in iron filled multiwall carbon nanotubes

We report on the electrical transport properties of single multiwall carbon nanotubes with and without an iron filling as a function of temperature and magnetic field. For the iron filled nanotubes the magnetoresistance shows a magnetic behavior induced by iron, which can be explained by taking into account a contribution of s-d hybridization. In particular, ferromagnetic-like hysteresis loops were observed up to 50 K for the iron filled multiwall carbon nanotubes. The magnetoresistance shows quantum interference phenomena such as universal conductance fluctuations and weak localization effects.     

A rate-dependent thermo-electro-mechanical free energy model for perovskite type single crystals

The three-dimensional electro-mechanical free energy potential developed by Kim and Seelecke [S.J. Kim and S. Seelecke, A rate-dependent three-dimensional free energy model for ferroelectric single crystals, Int. J. Solids Struct. 44 (2007) 1196-1209] is generalized to model various thermal aspects of perovskite type single crystals. A total of seven energy potentials are described in the 10-dimensional space of electric displacement vector, strain tensor and temperature, the first six of them representing the six distinct types of ferroelectric tetragonal variants and the seventh the paraelectric cubic phase of the materials. Energy barrier expressions given as functions of thermodynamic driving forces are combined with evolution equations to determine the phase fractions based on the theory of thermally activated processes, thus allowing for a natural treatment of rate-dependent effects. The thermodynamic Clausius-Clapeyron relation is derived from the energy potential and the double polarization hysteresis loops near Curie temperature observed by Merz [W.J. Merz, Double hysteresis loop of BaTiO₃ at the Curie point, Phys. Rev. 91 (1953) 513-517] are predicted and compared. Besides, various nonlinear coupling behavior, such as variation of spontaneous polarization over temperature, mechanical depolarization, and rate-dependent hysteresis loops, are calculated and discussed.     

Influence of long-range dipolar interactions on the phase stability and hysteresis shapes of ferroelectric and antiferroelectric multilayers

Phase transition and field driven hysteresis evolution of a two-dimensional Ising grid consisting of ferroelectric–antiferroelectric multilayers that take into account the long range dipolar interactions were simulated by a Monte–Carlo method. Simulations were carried out for a 1 + 1 bilayer and a 5 + 5 superlattice. Phase stabilities of components comprising the structures with an electrostatic-like coupling term were also studied. An electrostatic-like coupling, in the absence of an applied field, can drive the ferroelectric layers toward 180° domains with very flat domain interfaces mainly due to the competition between this term and the dipole–dipole interaction. The antiferroelectric layers do not undergo an antiferroelectric-to-ferroelectric transition under the influence of an electrostatic-like coupling between layers as the ferroelectric layer splits into periodic domains at the expense of the domain wall energy. The long-range interactions become significant near the interfaces. For high periodicity structures with several interfaces, the interlayer long-range interactions substantially impact the configuration of the ferroelectric layers while the antiferroelectric layers remain quite stable unless these layers are near the Neel temperature. In systems investigated with several interfaces, the hysteresis loops do not exhibit a clear presence of antiferroelectricity that could be expected in the presence of anti-parallel dipoles, i.e., the switching takes place abruptly. Some recent experimental observations in ferroelectric–antiferroelectric multilayers are discussed where we conclude that the different electrical properties of bilayers and superlattices are not only due to strain effects alone but also due to long-range interactions. The latter manifests itself particularly in superlattices where layers are periodically exposed to each other at the interfaces.     

Ag/Bi4Ti3O12/p-Si异质结的制备及其C-V特性研究

为制备符合铁电存储器件要求的高质量铁电薄膜,采用溶胶-凝胶(Sol-Gel)工艺,制备了Si基Bi4Ti3O12铁电薄膜及MFS结构的Ag/Bi4Ti3O12/P-Si异质结,对Bi4Ti3O12薄膜的相结构特征及异质结的C-V特性进行了测试与分析.XRD图谱显示,Si基Bi4Ti3O12薄膜具有沿c-轴择优取向生长的趋势,而Ag/Bi4Ti3O12/p-Si异质结顺时针回滞的C-V特性曲线则表明,该异质结可实现电极化存储.此外,对该异质结C-V特性曲线的非对称及向负偏压方向偏移的产生原因也进行了分析.在此基础上,为提高铁电薄膜的铁电性能及改善其C-V特性提出了合理的结构设想.     

溶胶-凝胶法制备Bi0.975La0.025Fe0.975Ni0.025O3铁电薄膜的结构及物理性能

采用溶胶-凝胶法在Pt/Ti/SiO_2/Si(111)衬底上制备了Bi_(0.975)La_(0.025)Fe_(0.975)Ni_(0.025)O_3(BLFNO)铁电薄膜。利用X射线衍射(XRD)、原子力显微镜(AFM)及其压电模式(PFM)对薄膜的晶体结构、表面形貌以及铁电畴结构进行了研究。研究发现,BLFNO为结晶良好的钙钛矿结构多晶薄膜,且薄膜表面颗粒生长均匀。PFM测试图显示铁电薄膜在自发极化下的铁电畴结构清晰,铁电电容器具有良好的铁电性能。应用铁电测试仪对Pt/BLFNO/Pt电容器进行测量,得到了饱和性良好的电滞回线。在828kV/cm的外加电场下,Pt/BLFNO/Pt电容器的剩余极化强度为74.3μC/cm~2,表明La、Ni的共掺杂没有明显抑制铁电电容器的剩余极化强度,铁电电容器具有良好的铁电性能。漏电流研究结果表明,La、Ni元素的共掺杂有效降低了薄膜的漏电流密度,在277.8kV/cm外加电场下漏电流密度在10-4 A/cm2量级,明显小于纯BFO薄膜的漏电流密度。正半支漏电流曲线满足SCLC导电机制,对于负半支曲线,当电场强度大于22.2kV/cm时,同样遵循SCLC导电机制;但是,当电场强度小于22.2kV/cm时,曲线斜率约为4.8,表明参与导电贡献的电子数较多,归因于极浅陷阱俘获的电子在外加电场作用下参与了导电行为。室温下磁滞回线测试结果表明BLFNO薄膜具有反铁磁性质。     

Magnetocapacitance in BaTiO3-CoFe2O4 nanocomposites

We report on the magnetoelectric characterization of epitaxial CoFe₂O₄-BaTiO₃ nanocomposites grown by rf sputtering on Nb-doped SrTiO₃ (001). Multiferroicity of the material is corroborated with both, ferroelectric and ferromagnetic hysteresis loops. Magnetoelectric coupling is investigated via magnetocapacitance measurements; a change of the capacitance of about 2% is observed for an applied magnetic field of 8 T. The possible origins of this magnetocapacitance are discussed.