Interface-related switching behaviors of amorphous Pr_0.67Sr_0.33MnO₃-based memory cells

The resistive switching properties in amorphous Pr0.67Sr0.33MnO3 films deposited by pulsed laser deposition are investigated.Reproducible and bipolar counter-8-shape and 8-shape switching behaviours of Au/Pr0.67Sr0.33MnO3 /F:SnO2 junctions are obtained at room temperature.Dramatically,the coexistence of two switching polarities could be reversibly adjusted by an applied voltage range.The results allocated those two switching types to areas of different defect densities beneath the same electrode.The migration of oxygen vacancies and the trapping effect of electrons under an applied electric field play an important role.An interface-effect-related resistance switching is proposed in an amorphous Pr0.67Sr0.33MnO3-based memory cell.     

Homogeneous interface-type resistance switching in Au/La0.67Ca0.33MnO3/SrTiO3/F:SnO2 heterojunction memories

La0.67Ca0.33MnO3 thin films are fabricated on fluorine-doped tin oxide conducting glass substrates by a pulsed laser deposition technique with SrTiO3 used as a buffer layer. The current-voltage characteristics of the heterojunetions exhibit an asymmetric and resistance switching behaviour. A homogeneous interface-type conduction mechanism is also reported using impedance spectroscopy. The spatial homogeneity of the charge carrier distribution leads to field- induced potential-barrier change at the Au-La0.67Ca0.33MnO3 interface and a concomitant resistance switching effect. The ratio of the high resistance state to the low resistance state is found to be as high as 1.3 x 10^4% by simulating the AC electric field. This colossal resistance switching effect will greatly improve the signal-to-noise ratio in nonvolatile memory applications.     

Charge ordering modulations in a Bi_0.4Ca_0.6MnO₃ film with a thickness of 110 nm

The low temperature sample stage in a transmission electron microscope is used to investigate the charge ordering behaviours in a Bi 0.4 Ca 0.6 MnO 3 film with a thickness of 110 nm at 103 K.Six different types of superlattice structures are observed using the selected-area electron diffraction(SAED) technique,while three of them match well with the modulation stripes in high-resolution transmission electron microscopy(HRTEM) images.It is found that the modulation periodicity and direction are completely different in the region close to the Bi 0.4 Ca 0.6 MnO 3 /SrTiO 3 interface from those in the region a little further from the Bi 0.4 Ca 0.6 MnO 3 /SrTiO 3 interface,and the possible reasons for this are discussed.Based on the experimental results,structural models are proposed for these localized modulated structures.     

The influence of interfacial barrier engineering on the resistance switching of In₂O₃:SnO₂/TiO₂/In₂O₃:SnO₂ device

The I–V characteristics of In2O3:SnO2/TiO2/In2O3:SnO2 junctions with different interfacial barriers are inves- tigated by comparing experiments. A two-step resistance switching process is found for samples with two interfacial barriers produced by specific thermal treatment on the interfaces. The nonsynchronous occurrence of conducting filament formation through the oxide bulk and the reduction in the interfacial barrier due to the migration of oxygen vacancies under the electric field is supposed to explain the two-step resistive switching process. The unique switching properties of the device, based on interfacial barrier engineering, could be exploited for novel applications in nonvolatile memory devices.     

La0.67Ca0.33MnO3薄膜中的各向异性应变与电荷有序

本文采用脉冲激光沉积法在NdGaO3(001)单晶衬底上制备了一系列的La0.67Ca0.33MnO3薄膜,实验主要研究了薄膜的输运性质.La0.67Ca0.33sMnO3块材是铁磁金属基态,而La0.67Ca0.33MnO3/NdGaO3(001)薄膜由于各向异性应变的存在,可以观测到电荷有序绝缘相的出现.薄膜样品表...     

Fe3O4 Segregation and Transport Properties of La0.67Ca0.33MnO3

Effect of Fe3O4 segregation at grain boundaries on the electrical transport and magnetic properties of La0.67Ca0.33MnO3 is investigated. The experimental results show that the Fe3O4 segregation not only shifts the paramagnetic-ferromagnetic transition temperature of La0.6TCa0.33MnO3 to a lower temperature region but also induces a new transition in a lower temperature region. Meanwhile, the transition processes observed in both the resistivity and magnetization curves are obviously widened. Compared to pure La0.67Ca0.33MnO3, we assume that the Fe3O4 segregation level at the grain boundaries can modify the electrical transport and magnetic properties of La0.67Ca0.33MnO3.     

La0.67Ca0.33MnO3复合体系的磁电阻增强效应

在La0.67Ca0.33MnO3(LCMO)纳米颗粒体系中,采用Cu与之复合,考察复合对磁电阻性能的影响.结果表明,复合使低场磁电阻得到大幅度的增强.但和其它LCMO复合体系截然不同的是,复合体系的电阻率大幅下降.认为是在LCMO颗粒周围形成一层良导体,电子输运与颗粒边界的电子散射有关.     

La0.67Ca0.33MnO3多晶薄膜电流效应

研究了在不同电流下多晶La0.67Ca0.33MnO3薄膜的电输运特性.观察到电阻随着电流的增大而减小,在多晶样品中当外加电流为1mA时负的电电阻(ER)即达到30%.同时,电流对于磁阻(MR)也有影响.考虑多晶样品中晶界的作用,我们提出了极化电流传输模型,对所观察到的实验现象进行了解释.     

The concentration quenching and crystallographic sites of Eu²⁺ in Ca₂BO₃Cl

A yellow phosphor, Ca2BO3 Cl:Eu2+ , is prepared by the high-temperature solid-state method. Under the condition of excitation sources ranging from ultraviolet to visible light, efficient yellow emission can be observed. The emission spectrum shows an asymmetrical single intensive band centred at 573 nm, which corresponds to the 4f 6 5d 1 →4f 7 transition of Eu2+ . Eu2+ ions occupy two types of Ca2+ sites in the Ca2BO3 Cl lattice and form two corresponding emission centres, respectively, which lead to the asymmetrical emission of Eu2+ in Ca2 BO 3 Cl. The emission intensity of Eu2+ in Ca2BO3 Cl is influenced by the Eu2+ doping concentration. Concentration quenching is discovered, and its mechanism is verified to be a dipole–dipole interaction. The value of the critical transfer distance is calculated to be 2.166 nm, which is in good agreement with the 2.120 nm value derived from the experimental data.     

Microphase separation in Pr0.67Ca0.33MnO3 by small-angle neutron scattering

We have evidenced by small-angle neutron scattering at low temperature the coexistence of ferromagnetism (F) and antiferromagnetism (AF) in Pr0.67Ca0.33MnO3. The results are compared to those obtained in Pr0.80Ca0.20MnO3 and Pr0.63Ca0.37MnO3, which are F and AF, respectively. Quantitative analysis shows that the small-angle scattering is not due to a mesoscopic mixing but to a nanoscopic electronic and magnetic "red cabbage" structure, in which the ferromagnetic phase exists in the form of thin layers in the AF matrix (stripes or 2D "sheets").     

Tunable Ba_0.5 Sr_0.5 TiO₃ film bulk acoustic resonators using SiO₂ /Mo Bragg reflectors

Tunable and switchable Ba 0.5 Sr 0.5 TiO 3 film bulk acoustic resonators(FBARs) based on SiO 2 /Mo Bragg reflectors are explored,which can withstand high temperature for the deposition of Ba x Sr 1 x TiO 3(BST) films at 800 C.The dc bias-dependent resonance may be attributed to the piezoelectricity of the BST film induced by an electrostrictive effect.The series resonant frequency is strongly dc bias-dependent and shifts downwards with dc bias increasing,while the parallel resonant frequency is only weakly dc bias-dependent and slightly shifts upwards at low dc bias(< 45 V) while downwards at higher dc bias.The calculated relative tunability of shifts at series resonance frequency is around 2.3% and the electromechanical coupling coefficient is up to approximately 8.09% at 60-V dc bias,which can be comparable to AlN FBARs.This suggests that a high-quality tunable BST FBAR device can be achieved through the use of molybdenum(Mo) as the high acoustic impedance layer in a Bragg reflector,which not only provides excellent acoustic isolation from the substrate,but also improves the crystallinity of BST films withstanding higher deposition temperature.     

Anomalous acoustoelectric effect in La0.67Ca0.33MnO3 films

We have studied the acoustoelectric (AE) effect produced by surface acoustic waves (SAW) in a monolithic layered structure, composed of a piezodielectric LiNbO3 substrate and a La0.67Ca0.33MnO3 film. The experiments unexpectedly revealed in the longitudinal AE effect an anomalous contribution, invariant upon reversal of SAW propagation, which coexists with the ordinary (odd in wave vector) effect. The anomalous effect dominates near the metal-insulator transition, while the ordinary effect prevails at high and low temperatures. We show that the anomalous effect is caused by strong modulation of the film conductivity produced by the SAW elastic deformations.     

Influence of the Jahn-Teller distortion on magnetic ordering in TbMn_1-xFe_xO₃

The Jahn-Teller distortion plays an important role in determining the exchange interaction in rare-earth manganites.In this work we study the influence of the Jahn-Teller distortion on the magnetic structures of TbMn1-xFexO3(x = 0,0.02,0.05,0.10,and 0.20) single crystals in the basal MnO2 plane.The decrease in the quadruple splitting with the increasing Fe doping indicates the reduction of the Jahn-Teller distortion,which makes the nearest neighboring(NN) FM interaction dominant over the next nearest neighbor(NNN) AFM interaction.This alteration is favorable for the development of A-type AFM ordering instead of the spiral magnetic ordering,which collapses when x ≥ 0.05.The analysis of dielectric data indicates that the ferroelectricity is arising from the peculiar spiral magnetic ordering.     

三元配合物Eu(BA)3PIP和 Eu(BA)3phen的制备与发光性质

合成了邻菲罗啉(phen)衍生物2-苯基-咪唑并 -1,10-菲罗啉(PIP),并以其为第二配体,苯甲酸(BA)为第一配体,制备出新型稀土铕三元有机配合物Eu(BA)₃PIP;在相同条件下,第一配体不变,1,10-菲罗啉为第二配体,还制备出Eu(BA)₃phen。采用元素分析、红外光谱、热重和差热分析等技术对合成的配体PIP及配合物Eu(BA)₃PIP和Eu(BA)₃phen进行了表征。通过发光光谱研究了配合物的发光性质,结果表明第二配体PIP有较大的共轭体系,在紫外光激发下,配合物中的配体可将吸收的能量传递给稀土Eu³⁺离子,表现出较强的Eu³⁺离子的特征发射。两种配合物相比,Eu(BA)₃PIP的发光强度明显大于Eu(BA)₃phen的发光强度,说明适宜的第二配体对配合物有很好的敏化发光作用。     

Generation of a mid-infrared broadband polarized supercontinuum in As₂Se₃ photonic crystal fibers

A simplified structure of birefringent chalcogenide As 2 Se 3 photonic crystal fiber(PCF) is designed.Properties of birefringence,polarization extinction ratio,chromatic dispersion,nonlinear coefficient,and transmission are studied by using the multipole method,the finite-difference beam propagation method,and the adaptive split-step Fourier method.Considering that the zero dispersion wavelength of our proposed fiber is about 4 μm,we have analysed the mechanism of spectral broadening in PCFs with different pitches in detail,with femtosecond pulses at a wavelength of 4 μm as the pump pulses.Especially,mid-infrared broadband polarized supercontinuums are obtained in a 3-cm PCF with an optimal pitch of 2 μm.Their spectral width at 20 dB reaches up to 12 μm.In the birefringent PCF,we find that the supercontinuum generation changes with the pump alignment angle.Research results show that no coupling between eigenpolarization modes are observed at the maximum average power(i.e.,37 mW),which indicates that the polarization state is well maintained.     

Structure and magnetoresistance of La<Subscript>0.67</Subscript>Ca<Subscript>0.33</Subscript>MnO<Subscript>3</Subscript> films grown coherently on (001)NdGaO<Subscript>3</Subscript>

40-to 120-nm-thick (001)La_0.67Ca_0.33MnO₃ films grown through laser evaporation on (001)NdGaO₃ were studied. The lattice parameters of the La_0.67Ca_0.33MnO₃ films measured in the substrate plane (a_∥=3.851 Å) and along the normal to its surface (a_⊥=3.850 Å) practically coincided with that of the pseudocubic neodymium gallate. The unit-cell volume of the La_0.67Ca_0.33MnO₃ film was slightly smaller than that of stoichiometric bulk samples. The position of the maximum in the temperature dependence of electrical resistivity did not depend on the thickness of the La_0.67Ca_0.33MnO₃ film. The negative magnetoresistance (MR≈?0.25, H=0.4 T) of La_0.67Ca_0.33MnO₃ films reached a maximum at 239–244 K.     

Spectroscopic characterization of Yb:Sc₂O₃ transparent ceramics

Yb:Sc2O3 transparent ceramics are fabricated by a conventional ceramic process and sintering in H2 atmosphere. The room-temperature spectroscopic properties are investigated, and the Raman spectrum shows an obvious vibration characteristic band centred at 415 cm 1 . There are three broad absorption bands around 891, 937, and 971 nm, respectively. The strongest emission peak is centred at 1.04 μm with a broad bandwidth (11 nm) and an emission cross-section of 1.8×10 20 cm 2 . The gain coefficient implies a possible laser ability in a range from 990 nm to 1425 nm. The energy-level structure shows that Yb:Sc 2 O 3 ceramics have large Stark splitting at the ground state level due to their strong crystal field. All the results show that Yb:Sc2O3 transparent ceramics are a promising material for short pulse lasers.     

Elastically strained and relaxed La0.67Ca0.33MnO3 films grown on lanthanum aluminate substrates with different orientations

Physics of the Solid State - Structure of 40-nm thick La0.67Ca0.33MnO3 (LCMO) films grown by laser evaporation on (001) and (110) LaAlO3 (LAO) substrates has been investigated using the methods of...     

Diode-pumped laser and self-frequency-doubling properties of a Nd³⁺:Na₃La₉O₃(BO₃)₈ crystal

We report efficient, diode-pumped, self-frequency doubling (SFD) in the newly developed laser crystal Nd³⁺:Na₃La₉O₃(BO₃)₈ (Nd:NLBO). More than 730?mW of fundamental output power at 1072?nm was achieved with a slope efficiency of 16.2%. With incident pump power of 8?W, 29?mW of green cw laser emission at 536?nm was observed with proper phase matching. This initial performance and the good optical properties of the crystalline host are encouraging for the development of a high power diode-pumped SFD visible light laser source.     

Interface-related switching behaviors of amorphous Pr0.67Sr0.33MnO3-based memory cells

The resistive switching properties in amorphous Pr0.67Sr0.33MnO3 films deposited by pulsed laser deposition are investigated.Reproducible and bipolar counter-8-shape and 8-shape switching behaviours of Au/Pr0.67Sr0.33MnO3 /F：SnO2 junctions are obtained at room temperature.Dramatically,the coexistence of two switching polarities could be reversibly adjusted by an applied voltage range.The results allocated those two switching types to areas of different defect densities beneath the same electrode.The migration of oxygen vacancies and the trapping effect of electrons under an applied electric field play an important role.An interface-effect-related resistance switching is proposed in an amorphous Pr0.67Sr0.33MnO3-based memory cell.