氧非正分La0.9Ba0.1MnO3-δ/SrTiO3:Nb p-n异质结的整流特性研究

利用脉冲激光沉积技术在掺Nb的SrTiO₃衬底上制备了氧非正分La_0.9Ba_0.1MnO_3-δ/SrTiO₃:Nb p-n异质结.在20—300K这一较宽的温度范围内获得了光滑的整流曲线.整流实验表明：该p-n异质结的正向扩散电压V_D随着温度升高在薄膜金属—绝缘转变温度附近出现极大值,表现出与氧正分La_0.9Ba_{0. 关键词： 0.9}Ba_0.1MnO_3-δ薄膜')" href="#">La_0.9Ba_0.1MnO_3-δ薄膜 锰氧化物p-n结 整流性质     

Effect of an interface boundary on the magnetooptical and magnetotransport properties of La<Subscript>0.67</Subscript>Ca<Subscript>0.33</Subscript>MnO<Subscript>3</Subscript>/La<Subscript>0.67</Subscript>Sr<Subscript>0.33</Subscript>MnO<Subscript>3</Subscript> heterostructures

The optical, magnetooptical (Kerr effect and magnetotransmission), and magnetotransport properties of La_2/3Ca_1/3MnO₃/La_2/3Sr_1/3MnO₃ and La_2/3Ca_1/3MnO₃/SrTiO₃/La_2/3Sr_1/3MnO₃ heterostructures on SrTiO₃ substrates are studied. The contribution of the interface boundary to the magnetotransmission is typical of a material with a transitional composition. It is found that a 2-nm-thick SrTiO₃ spacer does not influence the shape and position of the magnetotransmission peak in a field normal to the surface of the heterostructure but increases the contribution of the upper layer to the magnetotransmission in the Voigt geometry and also enhances the magnetoresistance that is due to the tunneling of spin-polarized carriers through the spacer. The Kerr spectra taken of the heterostructures are typical of single-layer single-crystal films.     

Experimental evidence for a magnetic two-phase state in manganites

It is found that samples of manganites La_0.9Sr_0.1MnO₃ (single crystal), Eu_0.7A_0.3MnO₃ (A=Ca, Sr; ceramics), and La_0.1Pr_0.6Ca_0.3MnO₃ and La_0.84Sr_0.16MnO₃ (thin epitaxial films) that are either field-cooled (in a magnetic field) or zero-field-cooled differ in low-temperature magnetization, and the hysteresis loop of field-cooled samples exhibits a displacement. This displacement signifies that a ferro-antiferromagnetic state occurs in these samples. The exchange integral J～10^?6 eV is calculated from this displacement, which describes the exchange Mn-O-Mn coupling through the interface ferromagnetic droplet-antiferromagnetic matrix. The magnetoresistance and volume magnetostriction of La_1?x Sr_xMnO₃ single crystals exhibit similar dependences on x, temperature, and the magnetic field in the vicinity of the Curie point, which points to the fact that these dependences are due to the same reason, namely, the occurrence of a magnetic two-phase ferro-antiferromagnetic state caused by strong s-d exchange.     

A Magnetic resonance study of La1−x SrxMnO3 manganites

Single crystals of La_0.9Sr_0.1MnO₃ and La_0.8Sr_0.2MnO₃ manganites are examined using magnetic resonance in the temperature range 80–370 K. It is found that magnetostatic oscillations arise near the Curie temperature. The possible reasons for the appearance of additional lines in the ferromagnetic resonance (FMR) spectrum are considered, and the anisotropy field and the type of crystalline magnetic anisotropy in the La_0.8Sr_0.2MnO₃ compound are determined. It is shown that the crystalline magnetic anisotropy in the La_0.9Sr_0.1MnO₃ compound exhibits specific features associated with its type of crystal structure.     

High resistance modulation by the electric field based on La0.9Sr0.1MnO3/SrTiO3/Si structure

A field-effect configuration based on La_0.9Sr_0.1MnO₃/SrTiO₃/Si structure is fabricated on Si substrate by laser molecular-beam epitaxy. The resistance modulation by electric field of the La_0.9Sr_0.1MnO₃/SrTiO₃/Si structure is investigated in detail. An evident resistance modulation effect is observed at 80 K. The channel resistance modulation by field effect reaches 1.4×10⁷% and 2.6×10⁶% when V _DS are −2 and −6.5 V, respectively. The ON/OFF ratio of approximately 4000 is obtained. The present results are worthy of further investigations for potential applications of resistance modulation by electrostatic field in the heterostructures consisting of perovskite oxides and Si. Supported by the National Natural Science Foundation of China (Grant No. 50672120) and the National Basic Research Program of China (Grant No. 2004CB619004)     

Capacitance of the La0.67Sr0.33MnO3/(Ba,Sr)TiO3 interface induced by electric field penetration into the manganite electrode

(001)La_0.67Sr_0.33MnO₃/(001)(Ba_xSr_{1 ? x} TiO₃/(001)La_0.67Sr_0.33MnO₃(x= 0–0.25) three-layer heterostructures are grown by laser evaporation on (001)La_0.3Sr_0.7Al_0.65Ta_0.35O₃ single-crystalline substrates. In a wide temperature range (≈150 K), effective permittivity ? of (1000 nm)Ba_0.25Sr_0.75TiO₃ and (1000 nm)SrTiO₃ films grown obeys the relationship ? ～ (T ? T _CW)^?1, where T _CW is the Curie-Weiss temperature for related bulk crystals. Using experimental dependences ?(T), the capacitance of the (001)La_0.67Sr_0.33MnO₃/(001)Ba_xSr_1?x TiO₃ and (001)La_0.67Sr_0.33MnO₃/(001)SrTiO₃ interfaces, which is due to electric field penetration into the manganite electrode, is estimated (C _int≈4μF/cm²). At bias voltages of ± 2.5 V, the change in the permittivity of the STO and BSTO films in the heterostructures studied reaches 25 and 45%, respectively.     

Effect of thermal-annealing on the magnetoresistance of manganite-based junctions

Thermal-annealing has been widely used in modulating the oxygen content of manganites. In this work, we have studied the effect of annealing on the transport properties and magnetoresistance of junctions composed of a La0.9Ca0.1MnO3＋6 film and a Nb-doped SrTiO3 substrate. We have demonstrated that the magnetoresistance of junctions is strongly dependent on the annealing conditions： Prom the junction annealed-in-air to the junction annealedin-vacuum, the magnetoresistance near 0-V bias can vary from ～-60% to N～0. A possible mechanism accounting for this phenomenon is discussed.     

(La0.7Sr0.3MnO3)m(BiFeO3)n超晶格间隔的La0.7Sr0.3MnO3三明治结构制备及表征

采用射频磁控溅射的方法在SrTiO₃（001） 基片上制备了（La_0.7Sr_0.3MnO₃）_m（BiFeO₃）_n超晶格间隔的La_0.7Sr_0.3MnO₃三明治结构.X射线衍射分析证明（La_0.7Sr_0.3MnO_{关键词： 超晶格薄膜 电诱导效应 隧道效应}     

X-ray studies of the (La,Sr)MnO<Subscript>3</Subscript> perovskite manganite structure

X-ray studies of perovskite manganites (La_0.9Sr_0.1)_0.9MnO₃ and La_1?xSr_xMnO₃ (x = 0.1, 0.15, 0.2, 0.25) are reported. The atom positions and interatomic distances and angles are calculated as a function of Sr doping at room temperature using the FullProf software. The temperature dependences of the crystal lattice parameters and unit cell volume are investigated. The effects of structural and magnetic phase transitions on the crystal lattice parameters are studied in detail. The bulk magnetoelastic contribution to thermal expansion is studied experimentally and calculated.     

Preparation of the La0.8Sr0.2MnO3 films on STO and LAO substrates by excimer laser-assisted metal organic deposition using the KrF laser

La_0.8Sr_0.2MnO₃ films were prepared on SrTiO₃ (STO) and LaAlO₃ (LAO) substrates using excimer laser-assisted metal organic deposition (ELAMOD). For the LAO substrate, no epitaxial La_0.8Sr_0.2MnO₃ film was obtained by laser irradiation in the fluence range from 60 to 110 mJ/cm² with heating at 500 °C. On the other hand, an epitaxial La_0.8Sr_0.2MnO₃ film on the STO substrate was formed by laser irradiation in the fluence range from 60 to 100 mJ/cm² with heating at 500 °C. To optimize the electrical properties for an IR sensor, the effects of the laser fluence, the irradiation time and the film thickness on the temperature dependence of the resistance and temperature coefficient of resistance (TCR: defined as 1/R·(dR/dT)) of the LSMO films were investigated. An LSMO film on the STO substrate that showed the maximum TCR of 3.9% at 265 K was obtained by the ELAMOD process using the KrF laser.     

Unusual resistive switching induced by voltage in La0.7Sr0.3MnO3 thin films

The hysteretic and reversible resistive-switching effect was observed in La_0.7Sr_0.3MnO₃ films at room temperature. The resistive switching was found to be most obvious in films fabricated at 30 Pa oxygen pressure, and more distinct in films fabricated on SrTiO₃ substrates than those fabricated on LaAlO₃ substrates. Moreover, La_0.7Sr_0.3MnO₃ films fabricated at a certain oxygen pressure with indium electrodes showed double ‘8’ type current-voltage loops. Some of the results are explained by considering the influence of the interface effect, electrodes and oxygen vacancies, but the mechanism of the double ‘8’ type current-voltage loops remains an open question.     

Optical evidence for lattice polarons in lightly doped lanthanum manganites in paramagnetic state

The reflection and absorption spectra and the resistivity data for La_0.93Sr_0.07MnO₃, La_0.9Sr_0.1MnO₃, La_0.85Sr_0.15MnO₃, La_0.92Ca_0.08MnO₃ and La_0.85Ba_0.15MnO₃ single crystals have been collected and analyzed by using small lattice polaron theory. The activation energies of the polaron hop are determined. The lattice polarons are found to be dominated in the electronic transport and optical properties in the paramagnetic state in La_0.93Sr_0.07MnO₃, La_0.92Ca_0.08MnO₃ and La_0.85Ba_0.15MnO₃ crystals. It is shown that lattice polaron involves more than one Mn site.     

Dynamic process of photovoltaic effect in La0.9Sr0.1MnO3/SrNb0.01Ti0.99O3 heterojunction

The dynamic process of photoelectric effects in the La_0.9Sr_0.1MnO₃/SrNb_0.01Ti_0.99O₃ heterostructure is theoretically revealed by solving equations consisting of time dependent drift–diffusion, Richardson thermionic emission current, and Shockley–Read–Hall recombination. The calculated time dependent evolution of photovoltage and the variation of carrier concentration are obtained. Present results indicate that a smaller parallel resistance should result in faster photoelectric response, but reduce the peak value of the photovoltage in a La_0.9Sr_0.1MnO₃/SrNb_0.01Ti_0.99O₃ heterojunction. In addition, the increase of the carrier mobilities induced by applying higher energy photons can decrease the rise time but increase the peak value of the photovoltage.     

Pulsed laser deposition of atomically flat La1-xSrxMnO3 thin films using a novel target geometry

A new ablation target geometry is presented that was used to produce thin films of La_1-xSr_xMnO₃ grown heteroepitaxially on SrTiO₃ by pulsed reactive crossed-beam laser ablation. The films were grown in order to perform angle-resolved photoelectron spectroscopy, which demands that the surface be atomically flat. In situ and ex situ analysis shows that this condition was met, even after depositing to a thickness of over 100 nm. PACS 61.10.-i; 61.18.Bn; 68.47.Gh; 71.27.+a; 81.15.Fg     

Application of novel SIMS technique for imaging the active sites of oxygen reduction at the SOFC cathode/electrolyte interfaces

The oxygen reduction active sites were visualized around the O₂/SOFC cathode/electrolyte triple phase boundaries (TPB) by the¹⁶O/¹⁸O exchange techniques and secondary ion mass spectrometry (SIMS) analysis. The higher¹⁸O concentration is observed on the cathode top surfaces (La_0.9Sr_0.1MnO₃-mesh, Au-mesh, and Ag-porous), which suggested the promotion of oxygen adsorption and oxygen surface exchange at the cathode. The oxygen diffusion through the bulk of cathode occurred at the La_0.9Sr_0.1MnO₃-mesh and the Ag-porous cathodes, not at the Au-mesh cathode. On the YSZ surfaces after removing the cathode, the active sites for oxygen incorporation were analyzed by SIMS. The active sites for oxygen incorporation were at the La_0.9Sr_0.1MnO₃/YSZ interface as well as the TPB. On the other hand, the active sites for oxygen incorporation are limited to the TPB in the case of the Au-mesh removed YSZ surface. From the SIMS analysis, the expansion of the active sites for oxygen incorporation is less than a few μm from the TPB lines. Paper presented at the 8th EuroConference on Ionics, Carvoeiro, Algarve, Portugal, Sept. 16–22, 2001.     

Mössbauer and magnetic studies of the phase state of SrFe<Subscript>12</Subscript>O<Subscript>19</Subscript>/La<Subscript>0.9</Subscript>Ca<Subscript>0.1</Subscript>MnO<Subscript>3</Subscript> composites

The formation of an intermediate phase in SrFe₁₂O₁₉/La_0.9Ca_0.1MnO₃ composites was demonstrated for the first time using only Mössbauer spectroscopy. The SrFe₁₂O₁₉/La_0.9Ca_0.1MnO₃ composite was prepared by the two-stage (sol–gel and hydrothermal) synthesis with varying initial conditions. The X-ray diffraction studies showed that the composite consisted of two phases: well-formed structures of manganite La_0.9Ca_0.1MnO₃ and hexagonal ferrite SrFe₁₂O₁₉. It was found that nanocrystalline La_0.9Ca_0.1MnO₃ particles with size d ? 150 nm formed in the composites at the surface of plate-like SrFe₁₂O₁₉ crystallites. The Mössbauer studies showed that the composite contained additional (intermediate) phase La_0.9Ca_0.1Mn(Fe)O₃ that formed at the interface between SrFe12O19 and La_0.9Ca_0.1MnO₃ phases. The intermediate phase concentration increased with the molar content of La_0.9Ca_0.1MnO₃; in this case, the fraction of the surface of SrFe₁₂O₁₉ crystallites coated with La_0.9Ca_0.1MnO₃ increased, which led to the increase in the total area of the interface surface and the intermediate phase concentration.     

Magnetoresistance and interlayer exchange coupling in perovskite manganite junctions

We study magnetoresistance (MR) and interlayer exchange coupling (IEC) in perovskite manganite junctions. We show that in La_2/3Sr_1/3MnO₃/SrTiO₃/La_2/3Sr_1/3MnO₃ tunneling junctions, the MR ratio remains finite up to high temperatures near T_C of bulk manganites. In the case of La_2/3Ba_1/3MnO₃/LaNiO₃/La_2/3Ba_1/3MnO₃ metallic trilayers, we predict that the oscillation period of the IEC constant is dramatically changed by hole doping into the LaNiO₃ spacer, while the MR ratio is relatively unaffected.     

Oxygen pressure dependent interfacial polarization of perovskite oxide multilayers on Si substrates

The SrTiO₃/La_0.9Sr_0.1MnO₃ (STO/LSMO) multilayers were fabricated on n-Si (1 0 0) substrates using a computer-controlled laser molecular-beam epitaxy (MBE) technique at 1 × 10⁻² Pa and 2 × 10⁻⁴ Pa oxygen partial pressures, respectively. The dielectric properties of the multilayers (MLs) were investigated. The differences of the dielectric properties of the two samples were explained by an impedance analysis technique, which indicates that the interfacial polarization has a close relationship with the oxygen pressure.     

(BiFeO3)25/(La0.7Sr0.3MnO3)25 多层膜的光学和电学性质

采用射频磁控溅射方法在(001)SrTiO₃衬底上制备(001)取向的(BiFeO₃)₂₅/(La_0.7Sr_0.3MnO₃)₂₅多层膜.光学测试结果表明,1.3-2.1 eV范围内,相对于衬底而言多层膜光吸收增强; BiFeO₃的带隙为2.7 eV. 另外,结合绝缘介质导电模型分析了所测得的电流-电压数据,在所测试的温度及电压下,所制备的(BiFeO₃)₂₅/(La_0.7Sr_0.3MnO₃)₂₅多层膜的导电机理由空间电荷限制电导主导. 关键词： 多层膜 吸光度 空间电荷限制电导     

Nanosecond photoelectric effects in all-oxide p-n junction of La<Subscript>0.9</Subscript>Sr<Subscript>0.1</Subscript>MnO<Subscript>3</Subscript>/SrNb<Subscript>0.01</Subscript>Ti<Subscript>0.99</Subscript>O<Subscript>3</Subscript>

Nanosecond (ns) photoelectric effects have been observed in all-oxide p-n junctions of La_0.9Sr_0.1MnO₃/SrNb_0.01Ti_0.99O₃ for the first time. The rise time was about 23 ns and the full width at half maximum was about 125 ns for the open-circuit photovoltaic pulse when the La_0.9Sr_0.1MnO₃ thin film in the p-n junction was irradiated by a laser of ≈20 ns pulse duration and 308 nm wavelength. The photovoltaic sensitivity was 80 mV/MJ for a 308 nm laser pulse.