(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(La0.7Sr0.3MnO3)m(BiFeO3)n超晶格间隔的La0.7Sr0.3MnO3三明治结构.X射线衍射分析证明(La0.7Sr0.3MnO3)m(BiFeO3)n具有明显的超晶格结构.电流垂直于薄膜表面测得的电阻-温度关系表明.La0.7Sr0.3MnO3)m(BiFeO3)n超晶格薄膜在290 K有金属-绝缘体转变,略低于单层La0.7Sr0.3MnO3薄膜的转变温度.电流在0.01-10 mA范围内,观察到薄膜的峰值电阻随电流增大而减小,峰值变化率远大于单层La0.7Sr0.3MnO3薄膜,且随着超晶格周期厚度的增加而增大.低温下,电流-电压曲线表明其导电机制应主要为空间载子限制,且显示较大的电压偏置,表现出肖特基结的特性.     

Crystallographic study of the rhombohedral-oriented domains in a La0.7Sr0.3MnO3 film

The microstructures present in a thin film of La_0.7Sr_0.3MnO₃, grown by computer-controlled laser molecular beam epitaxy on a SrTiO₃ (001) substrate, were characterized by means of cross-section and plan-view transmission electron microscopy. Four kinds of rhombohedral-oriented domains and two types of domain boundaries were identified in the film. The crystallographic relationships between each domain and the substrate were established on the basis of a hexagonal unit cell using Miller–Bravais indices. A mechanism for the formation of the oriented domains is proposed from the viewpoint of the evolution of strain relaxation during film preparation.     

La0.7-xGdxSr0.3MnO3体系中的相分离

采用固相反应法制备了样品La0.7-xGdxSr0.3MnO3(x=0.00,0.20,0.30,0.40,0.50).通过测量样品的M～T曲线,ESR曲线,研究了La0.7-xGdxSrO0.3MnO3,体系中的相分离现象及相分离与CMR之间关系.结果表明:当x=0.30,0.40时,在PM-FM相变区产生相分离,并且磁电阻MR得到增强.研究结果表明:La0.7-xGdx Sr0.3MnO3中的相分离与Gd在A位的占位情况紧密相关,磁电阻MR的增强是在外磁场作用下,铁磁区扩大顺磁区减小引起的.     

利用TG-FTIR联用仪研究纳米晶La_(0·7)Sr_(0·3)MnO_3的凝胶晶化过程

采用TG-FTIR联用仪对用溶胶-凝胶(sol-gel)法制备的纳米晶La0.7Sr0.3MnO3(L7S3)的凝胶晶化过程进行了研究,结果表明,复合干凝胶分解生成纳米晶粉是通过逐步分解分阶段形成的。     

Magneto-transport properties of La0.7Ca0.3MnO3/SrTiO3/La0.7Ce0.3MnO3 tunnel junction

Hole-doped rare-earth manganite La_0.7Ca_0.3MnO₃ and the electron-doped manganite La_0.7Ce_0.3MnO₃ both show a metal-insulator transition around 250 K associated with a ferromagnetic transition and colossal magnetoresistance. In an earlier publication we have reported the rectifying characteristic of La_0.7Ca_0.3MnO₃/SrTiO₃/La_0.7Ce_0.3MnO₃ tunnel junction at room temperature, showing that it is possible to fabricate a diode out of the polaronic insulator regime of doped manganites. Here we report the magneto-transport properties of such a tunnel junction above and below the metal-insulator transition. We show, from the large positive magnetoresistance of the tunnel junction at low temperature, that La_0.7Ce_0.3MnO₃ could be a minority spin carrier ferromagnet. The implication of this observation is discussed.     

Magnetic properties of La0.7Sr0.3MnO3 manganite films obtained by extraction pyrolysis

The structural and magnetic properties of manganite films obtained for the first time by extraction pyrolysis have been experimentally investigated. It has been established that at annealing temperatures T ≈ 600 K the films are fine-grained and have spin-glass-like magnetic properties. Prolonged annealing at T ≥ 700 K results in grain overgrowth and ferromagnetic behavior.     

Magnetooptical faraday effect in La0.7Sr0.3MnO3−δ films

The Faraday effect spectra were measured in La_0.7Sr_0.3MnO_3−δ films. A band attributed to d-d transitions ⁴ A _2g -⁴ T _2g in Mn⁴⁺ ions or octahedral complexes (MnO₆)⁸⁻ was observed in the spectral region of ∼2.7 eV. The position and value of the maximum of the Faraday rotation band and the figure of merit were found to depend on the degree of charge and magnetic uniformity of the films. The films can be used to develop mag-netooptical modulators.     

Magnetic and magnetooptical properties of polycrystalline films of La0.7Sr0.3MnO3

Magnetic circular dichroism (MCD) is studied in comparison with the magnetic behavior of polycrystalline films of La_0.7Sr_0.3MnO₃ (LSMO) deposited on a single crystal of zirconium oxide stabilized by yttrium (YSZ). It is found that the bands observed in MCD spectra are characterized by different temperature dependences.     

纳米多晶La0.7Sr0.3MnO3-δ的输运性质和磁电阻效应研究

利用溶胶-凝胶法制备了纳米多晶La0.7Sr0.3MnO3-δ(LSM)块体样品.详细研究了在不同烧结温度下的ISM样品电阻率随测量温度的变化关系和磁电阻效应.随着测量温度从室温降低,电阻率ρ都在250K附近存在最大值,低于该温度后,样品表现为金属导电特性,随后在50K左右存在一极小值.即随着温度从50K左右降低到4.2K,ρ反而逐渐升高,表现为绝缘体性的导电特性.研究表明,在低温下(＜50K),ρ随温度降低而升高的现象与隧穿效应的理论模型(lnρT1/1符合得很好,表明这种现象是由于传导电子在通过邻近LSM晶粒间表面/界面层时的隧道效应所致.而在50-250K的温度范围内,其电阻率与T2成正比,表现为LSM本征的金属导电特性.因此这种低温下电阻率的极小值现象来源于隧穿效应和LSM晶粒本征的金属导电特性的相互竞争.本文还详细研究了相应的隧道磁电阻效应.     

In-plane structural order of domain engineered La0.7Sr0.3MnO3 thin films

We present a detailed structural study of tensile-strained La_0.7Sr_0.3MnO₃ thin films. We use the substrate miscut to control the number of rhombohedral variants in the films and study the in-plane order and structural distortions. Using high-resolution X-ray diffraction, we demonstrate that step-edge induced lattice modulations occur in 4-variant films, whereas periodic twinning is the dominant in-plane order for 2-variant films. We show that the in-plane twinning angle is almost completely relaxed. However, the relaxation of shear strain by the out-of-plane twinning angle and the monoclinic distortion is only partial. Furthermore, the film thickness dependence of the domain width reveals that domain formation is a universal mechanism for shear strain relaxation. Finally, we show that the structural response to the transition from the paramagnetic to the ferromagnetic phase of La_0.7Sr_0.3MnO₃ at 345?K is smaller in 4-variant films compared to 2-variant films.     

Finite size effect and phase diagram of ultra-thin La0.7Sr0.3MnO3

La_0.7Sr_0.3MnO₃ (LSMO) ultra-thin films have been grown by pulsed laser deposition in conditions optimized for cation stoichiometry and bulk-like physical properties in the thick limit. Through electrical transport and magnetic measurements, a phase diagram is constructed as a function of film thickness. With decreasing thickness, the LSMO films cross over at high temperatures from a paramagnetic metal to a paramagnetic insulator, and at low temperatures from a ferromagnetic metal to a ferromagnetic insulator, in close similarity to that observed for varying the electronic bandwidth in bulk manganites.     

Temperature evolution of anisotropic stress induced highly ordered stripe magnetic domains in La0.7Sr0.3MnO3 thin film on (110) NdGaO3 substrate

Highly ordered ferromagnetic (FM) domain patterns with out-of-plane magnetization have been observed in La_0.7Sr_0.3MnO₃ (LSMO) thin film on (110) NdGaO₃ (NGO). Crystal structure and strain state analyses show that this remarkable domain pattern originates from the in-plane anisotropic stress induced by the substrate. Magnetic force microscope (MFM) images at different temperatures show that the FM domain contrast gradually decreases upon heating and disappears around the transition temperature. The root mean square (RMS) of the MFM images coincides with the resistivity measurement, suggesting that the change in resistivity with temperature is mainly due to carrier scattering by thermal spin fluctuation.     

Magnetization and magnetic circular dichroism of La0.7Sr0.3MnO3/YSZ polycrystalline films

The magnetic and magneto-optical properties as well as the surface morphology and structure of La_0.7Sr_0.3MnO₃ polycrystalline films of different thicknesses have been investigated. It has been shown that films have a rough surface with a characteristic in-plane linear dimension of ～30 nm, and crystallites with linear dimensions of 10–20 nm are randomly oriented in the plane. The temperature and field dependences of the magnetization of the films indicate their magnetic inhomogeneity. The magnetic circular dichroism spectra contain a number of bands, one of which at 2.4 eV is explained by the contribution of conduction electrons.     

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La0.7Sr0.3MnO3(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.这种现象是由于传导电子在通过邻近LSM晶粒间表面/界面层时的隧道效应所导致的.这种低温下电阻率的极小值现象来源于隧穿效应和LSM晶粒本征的金属导电特性的相互竞争.还详细研究了相应的隧道磁电阻效应的温度依赖性.     

Transport properties in La0.7-xGdxSr0.3MnO3 system

The influence of Gd doping at La-site on the electrical transport properties and the colossal magnetoresistance of La0.7-xGdxSr0.3MnO3 (x = 0.00, 0.10, 0.15, 0.20, 0.30, 0.40, 0.50, 0.60, and 0.70) is studied. The experimental results indicate that the transport properties exhibit abnormal behavior under high doping condition. For x = 0.50, we find that a transition from metal to insulator occurs after the occurrence of insulator-metal transition near Tc, which seldom occurs in ABO3 structure. For samples x = 0.60 and 0.70, it exhibits insulator behavior far above Tc. These abnormal behaviors are attributed to different magnetic background, i.e. the system undergoes a transition from long range ferromagnetic order to the cluster-spin glass state and further to antiferromagnetic order.     

Laser‐induced magnetisation dynamics in La0.7Sr0.3MnO3/SrRuO3 superlattices

Laser‐induced magnetisation dynamics of a La_0.7Sr_0.3MnO₃/SrRuO₃ superlattice is studied by means of a single‐colour optical pump‐probe technique. Significant differences in the magnetisation dynamics of a superlattice with respect to the single layers of constituent materials are demonstrated. Below the Curie temperature T_C of SrRuO₃, laser‐induced ultrafast demagnetisation is found to be followed by a uniform precession of the magnetisation around its new equilibrium. The data is described within a simple model based on a displacive excitation of a precessional magnetisation dynamics. The model is shown to give a good fit to the experimental data. As the initial temperature approaches T_C, the oscillations get suppressed and eventually vanish. The magnetisation dynamics is shown to depend on whether the two distinct magnetisation vectors in the superlattice are ferromagnetically or antiferromagnetically aligned. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

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.     

Electric-pulse-induced resistance switching in Nd0.7Sr0.3MnO3 ceramics

Nonlinear and hysteretic current–voltage characteristics and electric-pulse-induced resistance (EPIR) switching effects were found in Nd_0.7Sr_0.3MnO₃ ceramics. For samples measured using the two-wire method, a polarity-dependent, stable and reproducible EPIR effect occurs in the whole temperature range measured. The high and low resistive metastates vary with temperature and seemingly can be destroyed by temperatures larger than 400 K. However, for the same sample measured using the four-wire method, no EPIR effect is observed. The result indicates that the EPIR effect is intensively correlated with the interface between the Ag-electrodes and the bulk of the Nd_0.7Sr_0.3MnO₃ polycrystal.     

Dy的高掺杂对La0.7Sr0.3MnO3体系磁电性质的影响

通过实验研究了La0.7-xDyxSr0.3MnO3(x=0.00,0.30,0.40,0.50,0.60,0.70)体系的M-T曲线,M-H曲线,ρ-T曲线和MR-T曲线. 实验结果表明:随着Dy掺杂的增加,体系从长程铁磁有序向自旋团簇玻璃态、反铁磁及亚铁磁状态转变. x=0.30样品的M-T曲线上在TN附近出现磁化强度尖峰,x=0.40时尖峰消失. 对x=0.50样品,ZFC的M-T曲线随温度增加出现一个谷,随后在TN处出现峰;而FC的M-T曲线在低温下呈现负磁矩. 对x=0.60和0.70样品,不论FC还是ZFC的M-T曲线都类似于x=0.50的ZFC的M-T曲线. 高掺杂时的输运性质在其磁背景下发生异常. 这些奇异现象用Nel的双格子模型并联合M-H回滞曲线给予很好地解释.