系统的研究磁性的LaSr 2 Mn 2 O 7作为晶粒尺寸的函数提供了有关晶粒尺寸如何影响该化合物中的磁性和电荷有序的信息。半掺杂双层结构锰氧化物LaSr 2 Mn 2 O 7（x=0.5）在体相中具有CE型反铁磁（CE-AFM）电荷有序相变。在这项工作中，我们已经制备了LaSr 2 Mn 2 O 7陶瓷样品使用Pechini溶胶-凝胶法产生不同的晶粒尺寸和晶粒尺寸之间的影响150 - 200至1000 nm的磁性能的SQUID磁强计得到的结果进行了研究。所有样品的直流磁化（DCM）测量表明，晶粒尺寸对TCO没有相当大的影响。随着晶粒尺寸的减小，电荷有序峰的温度变得更尖锐，零场冷却（ZFC）和场冷却（FC）中的磁化率测量值增加。磁滞曲线的结果证实了反铁磁相的形成为基态，Arrott图表明在所有样品中存在一级和二级磁相变。此外，在样品的晶粒尺寸为150 - 200 nm，增强的磁性能，这是伴随着形成FM相的颗粒或颗粒的表面上，观察。
英文摘要：
Systematic studies of magnetic properties of LaSr2Mn2O7 as a function of crystalline grain size provide information on how the crystalline grain size affects the magnetic and charge ordering in this compound. The half-doped bi-layered manganite LaSr2Mn2O7 (x=0.5) in its bulk form has CE-type antiferromagnetic (CE-AFM) charge ordering phase transition. In this work, we have prepared LaSr2Mn2O7 ceramic samples using Pechini sol-gel method to produce different grain sizes and the effect of crystalline grain sizes between 150 200 to 1000 nm on magnetic properties results obtained by the SQUID magnetometer have been investigated. The DC magnetization (DCM) measurements for all samples indicate that the crystalline grain size has no considerable effect on TCO. Just the temperature of charge ordering peak becomes sharper, and susceptibility measurement in the zero field cooling (ZFC) and filed cooling (FC) increases as the grain sizes becomes systematically smaller. The results obtained from magnetic hysteresis curves confirm the anti-ferromagnetic phase formation as a ground state and Arrott plots obtained manifest the existence of first and second order magnetic phase transition in all samples. In addition, in sample with a grain size of 150 200 nm, enhancement of the magnetic properties, which is accompanied with the formation of FM phase on the surface of grain or particle, is observed.
Steplike Lattice Deformation of Single Crystalline (La$_{0.4}$Pr$_{0.6}$)$_{1.2}$Sr$_{1.8}$Mn$_{2}$O$_{7}$ Bilayered Manganite
本文报道了（La $_{0.4}$ Pr $_{0.6}$）$_{1.2}$ Sr $_{1.8}$ Mn $_{2}$ O $_{7}$双层锰氧化物的阶梯状晶格转变，并伴随着磁化和磁阻跃变，研究了场致一级相变的超尖锐性质，即从顺磁性绝缘体到铁磁性金属相的转变，并伴随着电阻的巨大下降.我们的研究结果支持，突然的磁致伸缩是密切相关的轨道挫折存在于不均匀的顺磁绝缘相，而不是竞争的两相之间的马氏体的情况。
Based on the two-variable polynomial model of magnetization, magnetic entropy change of bilayered manganites with $327$-structure and its scaling behaviour with respect to applied magnetic fields are investigated. It's found that the Curie temperature, which is defined as the point at which the partial derivative of magnetization with respect to temperature reaches its maximum, is different from the temperature of peak magnetic entropy change. Thus a mean-field model can not apply to this kind of manganites. In contrast to what has been found in manganites with the $113$-structure, the scaling…
Anomalous pressure effect on the remanent lattice striction of a (La,Pr)$_{1.2}$Sr$_{1.8}$Mn$_{2}$O$_{7}$ bilayered manganite single crystal
本文研究了（La，Pr）$ab$ Sr $_{1.8}$ Mn $_{2}$ O $_{7}$双层锰氧化物单晶在场致铁磁金属（FMM）相变温度范围内的压力效应。为了比较，我们还研究了在相应温度下磁化曲线的压力依赖性。外加压力降低了FMM转变的临界场，增强了回复磁致伸缩。观察到一个异常的压力效应的rexistine晶格弛豫，是类似的压力效应沿c轴的rexistine磁化。这些发现是从双交换相互作用驱动的FMM态通过施加压力而增强的观点来理解的。
Colossal electroresistance and colossal magnetoresistive step in paramagnetic insulating phase of single crystalline bilayered manganite(La$_{0.4}$Pr$_{0.6}$)$_{1.2}$Sr$_{1.8}$Mn$_{2}$O$_{7}$
我们报告了在（La $_{0.4}$ Pr $_{0.6}$）$_{1.2}$ Sr $_{1.8}$ Mn $_{2}$ O $_{7}$的顺磁绝缘（PMI）状态下在$ab$ -平面上施加电流引起的低温电阻的显著降低。在较低的温度下观察到一个巨大的电阻效应，达到~ 95%。在低于10 K的低温下，在5 T附近出现一个巨大的磁阻阶跃，并伴随着绝缘体-金属转变的超尖锐宽度。向晶体注入更高的电流会导致阶跃跃迁消失。这些发现与研究晶体的PMI矩阵内钉扎的短程电荷有序簇的存在有密切的关系。
One-dimensional (1D) confinement has been revealed to effectively tune the properties of materials in homogeneous states. The 1D physics can be further enriched by electronic inhomogeneity, which unfortunately remains largely unknown. Here we demonstrate the ultra-high sensitivity to magnetic fluctuations and the tunability of phase stability in the electronic transport properties of self-assembled electronically phase-separated manganite nanowires with extreme aspect ratio. The onset of magnetic nano-droplet state, a precursor to the ferromagnetic metallic state, is unambiguously revealed, wh…
Evidence for nano-scale inhomogeneities in bilayer manganites in the Mn\sp{4+} rich region: $\bm{0.54 \leq x \leq 0.80}$
采用原子对分布函数（PDF）技术研究了掺杂范围为$0.54 \leq x \leq 0.80$的天然双层锰氧化物\lsmo中原子的局域结构响应。我们的低温中子粉末衍射测量表明，当其有序磁结构从A型（$0.54 \leq x \leq 0.66$）向C/C型$^*$（$0.74 \leq x \leq 0.90$）有序过渡时，两种不同的Jahn-Teller（JT）畸变MnO $_6$八面体共存。在低温下，在所有掺杂水平下，掺杂空穴主要存在于双层的平面中。在A型磁有序区中，$_g$电子在平面上明显离域，形成未畸变的八面体，而在C/C型$^*$区中，JT畸变八面体明显拉长.这与非均匀共存的离域和局域电子态的存在是一致的。没有观察到宏观相分离的证据。这种纳米级的不均匀性可以解释在自旋无序的“间隙”区域（$0.66 \leq x \leq 0.74$）中观察到的磁阻挫行为。
Enhanced grain surface effect on magnetic properties of nanometric La0.7Ca0.3MnO3 manganite : Evidence of surface spin freezing of manganite nanoparticles
Despite extensive researches on manganites owing to widespread use in modern electronics, this class of metal oxides does not cease to surprise with its unique properties and new phenomena. Here we have studied structural and magnetic properties of non-Heisenberg manganite nanoparticles with a strong spin-electron coupling. During transition from low temperature ferromagnetic to high temperature paramagnetic state, the change in charge, valence and spin (magnetic moment) with the localization of eg-electrons on the manganese ions have been detected. With decrease in a temperature, the overstat…
We report a pervasive phenomenon of gradual emergence of negative magnetization in typical $R_{1-x}D_x$MnO$_3$ orthorhombic perovskite manganites in nano form (with $R^{3+}$ being a trivalent high-magnetic-moment ion from the heavier rare-earth elements Gd, Tb, Dy and $D^{2+}$ refers to divalent alkaline elements Sr, Ca, etc.), while the bulk form manifests no negative magnetization. Extensive magnetization studies have been carried out in Gd$_{1-x}$Ca$_x$MnO$_3$ manganites around half doping. We demonstrate experimentally that particle size reduction in nano-form manganites enhances the prope…
In this work we studied the influence of particle size and agglomeration in the performance of solid oxide fuel cell cathodes made with nanoparticles of La0.8Sr0.2MnO3. We followed two synthesis routes based on the Liquid Mix method. In both procedures we introduced additional reagents in order to separated the manganite particles. We evaluated cathodic performance by Electrochemical Impedance Spectroscopy in symmetrical (CATHODE/ELECTROLYTE/CATHODE) cells. Particle size was tuned by the temperature used for cathode sintering. Our results show that deagglomeration of the particles, serves to i…
A detailed nanoscale structural characterization was performed on high-quality La0.66Sr0.33MnO3 (LSMO) thin films of different thicknesses and deposited by pulsed laser deposition onto buffered Si (100) substrates. A multilayered structure built of Y0.13Zr0.87O2 (YSZ) and CeO2 layers was used as buffer in order to optimize the manganite films growth. The stacking of the different layers, their morpholohy, composition and strains were analysed using different experimental techniques. In-situ characterization of the films, performed with reflection high-energy electron diffraction, revealed thei…
Colossal magnetoresistance without phase separation: Disorder-induced spin glass state and nanometer scale orbital-charge correlation in half doped manganites
本文研究了高质量$A$位无序（固溶体）$_{0.5}$单晶在自旋玻璃绝缘体与磁阻铁磁金属相界附近的磁学和电学性质。详细分析了Eu $_{0.5}$ Ba $_{0.5}$ MnO $_3$的交流磁化率和X射线漫散射随温度的变化关系。具有小带宽的Ln $_{0.5}$ Ba $_{0.5}$ MnO $_3$晶体中随机势扰动的均匀性产生了均匀的短程电荷/轨道有序，而不是相分离，从而产生了近原子的自旋玻璃态。值得注意的是，这种微观无序的“CE玻璃”状态本身就能够产生巨大的磁阻。
Open Questions in CMR Manganites, Relevance of Clustered States, and Analogies with other Compounds
这是一篇非正式的论文，其中包含了锰氧化物中“我们知道的事情”和“我们不知道的事情”的列表。它改编自作者最近的一本书的结论章节，{ \it纳米级相分离和巨磁阻。The Physics of Manganites and Related Compounds}，Springer-Verlag，柏林，2002年11月。最近锰氧化物研究的主要新结果是发现了在实验和模型模拟中存在不均匀状态的趋势。巨磁阻效应似乎与这些混合相趋势密切相关，尽管需要更多的工作来充分证实这些想法。该文件还包括铜酸盐，稀磁半导体，弛豫铁电体，钴矿，有机和重费米子超导体的信息。这些材料潜在地与锰氧化物共享一些共同的现象学，例如高于反常行为开始的有序温度的温度标度$T^*$。这些材料中的许多还存在低温相竞争。简要讨论了在不涉及铁磁体的化合物中出现类铁磁效应的可能性。总体而言，它的结论是，不均匀的“集群”状态应被视为一个新的范例，在凝聚态物理，因为它们的存在似乎是更常见的比以前预期的。
Strong correlated manganites are still under intense research owing to their complex phase diagrams in terms of the Sr-doping and their sensitivity to intrinsic and extrinsic structural deformations. Here, we performed x-ray absorption spectroscopy measurements of manganites bilayers to explore the effects that a local Sr-doping gradient produce on the charge and antiferromagnetic anisotropies. In order to gradually tune the Sr-doping level along the axis perpendicular to the samples we have grown a series of bilayers with different thicknesses of low-doped manganites (from 0 nm to 6 nm) depos…
Perovskite manganite La0.5Ca0.5-x xMnO3 (LCMO) nanomaterials were elaborated using the sucrose modified auto combustion method. Rietveld refinements of the X-ray diffraction patterns of the crystalline structure confirm a single-phase orthorhombic state with Pbnm space group (No. 62). The Ca-vacancies were voluntarily created in the LCMO structure in order to study their influence on the magnetic behaviour in the system. The magnetic susceptibility was found to be highly enhanced in the sample with Ca-vacancies. Paramagnetic-to-ferromagnetic phase transition was evidenced in both samples aroun…
Evidence of electronic phase arrest and glassy ferromagnetic behaviour in (Nd0.4Gd0.3)Sr0.3MnO3 manganite : Comparative study between bulk and nanometric samples
Ferroelectric domain walls are attracting broad attention as atomic-scale switches, diodes and mobile wires for next-generation nanoelectronics. Charged domain walls in improper ferroelectrics are particularly interesting as they offer multifunctional properties and an inherent stability not found in proper ferroelectrics. Here we study the energetics and structure of charged walls in improper ferroelectric YMnO$_3$, InMnO$_3$ and YGaO$_3$ by first principles calculations and phenomenological modeling. Positively and negatively charged walls are asymmetric in terms of local structure and width…
We use femtosecond x-ray diffraction to study the structural response of charge and orbitally ordered Pr$_{1-x}$Ca$_x$MnO$_3$ thin films across a phase transition induced by 800 nm laser pulses. By investigating the dynamics of both superlattice reflections and regular Bragg peaks, we disentangle the different structural contributions and analyze their relevant time-scales. The dynamics of the structural and charge order response are qualitatively different when excited above and below a critical fluence $f_c$. For excitations below $f_c$ the charge order and the superlattice is only partially…
Complex many-body interaction in perovskite manganites gives rise to a strong competition between ferromagnetic metallic and charge ordered phases with nanoscale electronic inhomogeneity and glassy behaviors. Investigating this glassy state requires high resolution imaging techniques with sufficient sensitivity and stability. Here, we present the results of a near-field microwave microscope imaging on the strain driven glassy state in a manganite film. The high contrast between the two electrically distinct phases allows direct visualization of the phase separation. The low temperature microsc…
Interface-dominated materials such as nanocrystalline thin films have emerged as an enthralling class of materials able to engineer functional properties of transition metal oxides widely used in energy and information technologies. In particular, it has been proved that strain-induced defects in grain boundaries of manganites deeply impact their functional properties by boosting their oxygen mass transport while abating their electronic and magnetic order. In this work, the origin of these dramatic changes is correlated for the first time with strong modifications of the anionic and cationic …
Single domain to multi-domain transition due to in-plane magnetic anisotropy in phase separated (La$_{0.4}$Pr$_{0.6}$)$_{0.67}$Ca$_{0.33}$MnO$_{3}$ thin films
相分离的钙钛矿锰氧化物具有具有不同晶体结构、磁性和电子性质的竞争相。因此，应变效应在决定锰氧化物薄膜的磁性方面起着关键作用。本文报道了各向异性应力对相分离锰氧化物（La $_{0.4}$ Pr $_{0.6}$）$_{0.67}$ Ca $_{0.33}$ MnO $_{3}$磁性的影响。在面内各向异性应力下在（110）NdGaOPDMATHABMQ衬底上生长的（$_{0.4}$ Pr $_{0.6}$）$_{0.67}$ Ca $_{0.33}$ MnO $_{3}$薄膜显示出面内磁各向异性和单畴到多畴转变随温度的变化。角度相关的磁化测量也表明，磁化反转发生主要是通过成核$&$传播机制。通过与在（001）SrLaGaOPDMATHABMS衬底上生长的（$_{0.4}$ Pr $_{0.6}$）$_{0.67}$ $_{0.33}$ MnO $_{3}$薄膜的比较，证实了磁各向异性主要是由衬底诱导的各向异性应力引起的。我们的研究结果提出了在纳米磁性介质中存储磁信息的新途径。
