(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}     

(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     

［（SrTiO3）n/（SrTi0.8Nb0.2Ｏ3）m］20/LaAlO3超晶格的制备及其激光感生热电电压效应

采用脉冲激光沉积（PLD）镀膜技术在倾斜10°的LaAlO₃（100）单晶衬底上制备了（SrTiO₃）_n/（SrTi0.8Nb_0．2Ｏ₃）_m系列超晶格.在超晶格薄膜的XRD图谱中清楚地观察到周期调制的卫星峰结构.从卫星峰的分布计算了超周期,进而得到了在生长SrTiO₃和SrTi_0．8Nb_{0．2< 关键词： 3}）_n/（SrTi_0．8Nb_0．2Ｏ₃）_m］20/LAO（100）超晶格')" href="#">［（SrTiO₃）_n/（SrTi_0．8Nb_0．2Ｏ₃）_m］20/LAO（100）超晶格 激光感生热电电压 各项异性Seebeck系数 原子层热电堆     

Pr0.7(Sr1-xCax)0.3MnO3多晶体系中的小极化子性质

采用基于柠檬酸体系的溶胶-凝胶法制备了Pr_0.7（Sr_1-xCa_x）_0.3MnO₃系列的多晶块材, 同时还用脉冲激光沉积技术（PLD）在SrTiO₃（100）衬底上外延生长了同一系列的薄膜, 系统研究了它们的晶格结构和电输运行为. 多晶和薄膜样品都具有正交晶格结构, 电输运行为在居里温度T_Ｃ以上的高温顺磁相都很好 关键词： 0.7（Sr_1-xCa_x）_0.3MnO₃')" href="#">Pr_0.7（Sr_1-xCa_x）_0.3MnO₃ 绝热小极化子模型 双交换作用 Jahn-Teller晶格畸变     

La0.9Sr0.1MnO3薄膜中电流效应研究

用直流磁控溅射法在(100)LaAlO₃衬底上制备了La_0.9Sr_0.1MnO₃薄膜.经退火处理后薄膜的原子力显微镜形貌观测和X射线衍射分析显示具有比较好的质量.电阻率-温度关系表明La_0.9Sr_0.1MnO₃薄膜在281 K处发生金属绝缘体转变.电流在0.01—4 mA范围内，薄膜的峰值电阻率随电流增大而减小，在4 mA下获得了30.5%的峰值电阻率变 关键词： 掺杂锰氧化合物 0.9Sr_0.1MnO₃薄膜')" href="#">La_0.9Sr_0.1MnO₃薄膜 电流诱导效应 相分离理论     

多晶La0.7Sr0.3MnO3的低温输运性质和磁电阻效应

详细研究了由纳米晶粒组成的块体多晶La_0.7Sr_0.3MnO₃(LSM)的电阻率和磁电阻效应,以及它们的温度依赖性.随着温度从室温降低,电阻率(ρ)在250K附近存在一最大值,低于该温度后,样品表现为金属导电特性,随后在50K附近存在一极小值.也就是说在低于50K的温度范围内,随着温度降低ρ反而升高,表现为绝缘体性的导电特性.经研究发现,这种随温度降低ρ反而增加的现象与隧穿效应的理论模型(lnρ∝T^-1/2)符合得很好 关键词： 0.7Sr_0.3MnO₃')" href="#">多晶La_0.7Sr_0.3MnO₃ 隧道效应 隧道磁电阻效应     

Ti/Pr0.7Ca0.3MnO3/La0.67Sr0.33MnO3/Pt异质结电致电阻效应的改善

采用脉冲激光沉积技术制备了Ti/Pr_0.7Ca_0.3MnO₃/Pt和Ti/Pr_0.7Ca_0.3MnO₃/La_0.67Sr_0.33MnO₃/Pt异质结并研究了La_0.67Sr_0.33MnO₃功能插层对异质结电致电阻特性的影响. 实验结果表明La_0.67Sr_0.33MnO₃功能层的引入有效提高了器件的电阻转变特性,尤其是电阻转变率和疲劳性得到了极大的改善. 对La_0.67Sr_0.33MnO₃插层改善电致电阻转变特性的机理进行了定性的分析. 关键词： 电致电阻效应 电阻转变比率 疲劳特性     

Sr掺杂Eu1-xSrxMnO3体系的磁相变以及输运特性研究

对Eu_1-xSr_xMnO₃ (ESMO, x=0—1)体系的结构和磁性进行了系统的研究,结果表明Sr的掺入使EuMnO₃反铁磁母体的磁结构发生巨大的变化.通过磁化和电输运测量,深入探讨了高掺杂浓度Eu_0.4Sr_0.6MnO₃和Eu_0.3Sr_0.7MnO_{3关键词： 1-x}Sr_xMnO₃体系')" href="#">Eu_1-xSr_xMnO₃体系 Sr掺杂 可变程跳跃模型     

La0.3Sr0.7TiO3模板层对Pb(Zr0.5Ti0.5)O3薄膜的铁电性能增强效应的研究

通过sol-gel法在Si (111) 基片上分别制备了LaNiO₃(LNO)底电极和LaNiO₃/La_0.3Sr_0.7TiO₃ (LNO/LSTO)底电极.然后采用sol-gel 方法，在两种衬底上分别制备了Pb (Zr_0.5Ti_0.5)O₃ (PZT)铁电薄膜.XRD分析表明，两种PZT薄膜均具有钙钛矿结构，且在LNO底电极上的PZT薄膜呈(100) 择优取向，而在LNO/LSTO底电极上的PZT薄膜呈随机取向.铁电性能测试表明，相对LNO衬底上制备的PZT薄膜，在LNO/LSTO底电极上制备的PZT薄膜的剩余极化强度得到了有效的增强，同时矫顽场也增大.介电常数和漏电流的测试表明，LNO/LSTO底电极上制备的PZT薄膜具有大的介电常数和漏电流. 关键词： PZT薄膜 铁电性 漏电流 0.3Sr_0.7TiO₃')" href="#">La_0.3Sr_0.7TiO₃     

锰位铁掺杂La0.67Sr0.33FexMn1-xO3薄膜的光诱导效应

分别采用溶胶-凝胶法和脉冲激光沉积的方法制备了La_067Sr_033Fe_xMn_1-xO₃(x=0, 005, 010, 015)系列块材和薄膜,研究了Fe部分替代对La_067Sr_033Fe_xMn_1-xO₃薄膜 关键词： 光诱导 Fｅ掺杂 晶格效应     

Giant positive magnetoresistance in heterostructure (La<Subscript>0.7</Subscript>Sr<Subscript>0.3</Subscript>MnO<Subscript>3</Subscript>) coated with YBa<Subscript>2</Subscript>Cu<Subscript>3</Subscript>O<Subscript>7</Subscript> composites

(La_0.7Sr_0.3MnO₃) _x /(YBa₂Cu₃O₇) _y composites were prepared by mixing La_0.7Sr_0.3MnO₃ powders and the sol–gel-derived YBa₂Cu₃O₇ matrix, followed by high-temperature calcinations. Their structural, magnetic properties and magnetoresistance effect have been investigated systematically. A giant positive magnetoresistance (PMR) at low magnetic field is observed at low temperatures. In the case of (La_0.7Sr_0.3MnO₃)₁/(YBa₂Cu₃O₇)₉ composite, the PMR achieves 260% under a magnetic field of 5800 Oe. However, the PMR value sharply decreases with increasing temperature and no magnetoresistance effects are found above metal-insulator transition temperature. The enhancement of spin-dependent scattering at the grain boundaries should be responsible for the observed PMR. In addition, the temperature dependence of resistance under magnetic field could be explained by the competition between diamagnetism and paramagnetism in YBCO phase. At low temperature, the diamagnetism is predominant over paramagnetism and the interface scattering between LSMO grains is enhanced correspondingly. As a result, the low-temperature resistance increases and large PMR appears.     

Pressure-induced modifications of crystal and magnetic structure of oxygen deficient La<Subscript>0.7</Subscript>Sr<Subscript>0.3</Subscript>MnO<Subscript>3-d</Subscript> manganites

The crystal and magnetic structures of the oxygen deficient manganites La_0.7Sr_0.3MnO_3-d (d = 0.15, 0.20) have been studied by means of powder neutron diffraction over the 0–5.2 GPa pressure and 10–290 K temperature ranges. La_0.7Sr_0.3MnO_2.85 exhibits a coexistence of rhombohedral and tetragonal (I4/mcm) crystal structures and below T_g ~ 50 K a spin glass state is formed. La_0.7Sr_0.3MnO_2.80 exhibits a tetragonal (I4/mcm) crystal structure. Below T_g ~ 50 K a phase separated magnetic state is formed, involving coexistence of C-type AFM domains with spin glass domains. In both compounds the crystal structure and magnetic states remain stable upon compression. The factors leading to the formation of different magnetic states in La_0.7Sr_0.3MnO_3-d (d = 0.15, 0.20) and their specific high pressure behavior, contrasting with that of the stoichiometric A_0.5Ba_0.5MnO₃ (A = Nd, Sm) compounds showing pressure-induced suppression of the spin glass state and the appearance of the FM state, are analysed.     

Galvanomagnetic properties of La0.7Sr0.3Mn0.9Cu0.1O3

La_0.7Sr_0.3Mn_0.9Cu_0.1O₃ ceramic samples have been obtained by the conventional method of the solid-phase reaction, and their resistivity ρ has been investigated in a temperature range from 50 to 300 K in magnetic fields B = 0–20 T. Dependences are typical of perovskite manganites with a maximum at T _max = 140–150 K and an increase in ρ near T _max with increasing external magnetic field B. It has been established that the behavior of resistivity is caused by the variable range hopping conduction mechanism ρ(T) = ρ₀(T)exp[(T ₀/T)^1/4], where ρ₀(T) ～ T ^25/4. The Mott variable range hopping conduction has been observed below the Curie temperature for La_0.7Sr_0.3Mn_0.9Cu_0.1O₃ samples (T _C ～ 300 K) in a temperature range from 300 to 200 K. The influence of Cu doping on the properties of La_0.7Sr_0.3MnO₃ samples is apparently caused by an additional distortion introduced into the crystal lattice of the material and by a weakening of the double-exchange mechanism.     

Magnetocaloric effect in polycrystalline (La0.5Gd0.2)Sr0.3MnO3

In this paper, we present a study of magnetocaloric effect in the colossal magnetoresistance material (La_0.5Gd_0.2)Sr_0.3MnO₃. From the measurements of isothermal magnetization at different temperatures, we have discovered a large magnetic entropy change with a broad peak around Curie temperature (270.5 K) in (La_0.5Gd_0.2)Sr_0.3MnO₃ polycrystalline sample. Moreover, the maximum of magnetic entropy change exhibits a nearly linear dependence with applied high magnetic field. These results suggest that this material is a suitable candidate as working substance in magnetic refrigeration near room temperature.     

Properties of manganite/ruthenate superlattices with ultrathin layers

The properties of manganite/ruthenate superlattices are reviewed with a specific focus on the manganite/ruthenate interface. La_0.7Sr_0.3MnO₃/SrRuO₃ and Pr_0.7Ca_0.3MnO₃/SrRuO₃ superlattices grow with a high crystalline perfection as illustrated in the figure to the right: at the interface the individual cation species can be clearly identified, interdiffusion is marginal. The superlattices show magnetization processes with an intricate interplay between magnetocrystalline anisotropy, size of the layer magnetization, spin confinement and interfacial antiferromagnetic interlayer coupling. There is further an unprecedented Curie temperature stabilization at room temperature values of the La_0.7Sr_0.3MnO₃ layers in the superlattices down to layer thicknesses of one unit cell. The magnetotransport properties, especially the Hall effect, indicate the existence of a quasi‐two‐dimensional hole gas at the La_0.7Sr_0.3MnO₃/SrRuO₃ interface; this is further supported by an analysis of cation displacements as determined from scanning transmission electron microscopy. The manganite/ruthenate interface might be considered as a model system for the study of interfacial reconstruction and charge transfer in a highly correlated ferromagnetic system.

     

Laser patterning and magnetic properties of perovskite-type La0.7Sr0.3MnO3 crystals on the glass surface

The laser-induced crystallization technique has been applied to 10La₂O₃-35SrO-25MnO₂-30B₂O₃ glass (mol%) in order to examine the possibility of the formation and morphology control of perovskite-type La_1?xSr_xMnO₃ crystals on the glass surface. It is found from X-ray diffraction analyses that La_0.7Sr_0.3MnO₃ crystals are formed in the sample obtained by continuous wave Y b:Y V O₄ fiber laser (wavelength: 1080 nm) irradiations (power: 350 mW, scanning speed: 10 μm/s). La_0.7Sr_0.3MnO₃ manganites in the laser-irradiated samples are proposed to be ferromagnetic crystals having a Curie temperature of ～315 K from magnetization measurements and the Arrott plot. The surface morphology of laser-irradiated parts is not smooth, and La_0.7Sr_0.3MnO₃ crystals are present randomly without any orientations. It is clarified that Mn⁴⁺ ions in the glass act as suitable transition metal ions for the laser-induced crystallization.     

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.