A detailed study of the electric field gradient (EFG) across the Pr1-xCaxMnO3 phase diagram and its temperature dependence is given. Clearly, distinct EFG behaviours for samples outside/inside the charge order (CO) region are observed. The EFG temperature dependence evidences a new phase transition occurring over the broad CO region of the phase diagram. This transition is discontinuous and occurs at temperatures between the charge ordering and the Neel temperatures. The features observed in the EFG are associated with polar atomic vibrations which eventually lead to a spontaneous local electric polarization below CO transition.
The phase diagram of $Pr_{1-x}Ca_xMnO_3$ is modified x $\le$ 0.3, which suggests a reevaluation of the phase diagram of other manganites in that doping region. Rather than an orbital ordered phase reaching up to high temperatures of approximately 800-1100 K, we propose a loss of spontaneous orbital order already near room temperature. Above this temperature, the phase is characterized by a finite orbital polarization and octahedral tilt pattern. The tilt pattern couples to the Jahn-Teller distortion and thus induces a remaining orbital order, which persists up to high temperatures, where the t…
The Monte Carlo Ferromagnetic Ising model was used to study the electrical properties of manganese oxides due to the charge ordering phase occurring at doping, x = 0.5. The half-doped manganites have an insulator antiferromagnetic ground state. We calculated the internal energy, specific heat, resistivity and the magneto-resistance, MR, with parallel and anti-parallel applied magnetic fields. Our simulation reveals that the resistivity decreases exponentially and the electric current increases with increasing temperature according the free charge increase, to transport from an insulator to con…
Detailed investigations of structural, magnetic and electronic transport properties of hole-doped high-entropy rare-earth manganites are presented. The high-entropy samples (LaNdPrSmEu)$_{1-x}$Sr$_x$MnO$_3$ (0$\leq$\textit{x}$\leq$0.5), synthesized using the solid-state technique, show a change in the crystal structure from \textit{Pbnm} to \textit{R-3c} with increasing Sr substitution, attributed to the change in the tolerance factor. Prominent ferromagnetic ordering is observed in the sample with a rhombohedral structure (\textit{x}$\geq$0.3), originating from the dominant double exchange me…
Effect of suppression of local distortion on magnetic, electrical and thermal transport properties of Cr substituted bi-layer manganite LaSr$_{2}$Mn$_{2}$O$_{7}$
Colossal magnetoresistance is of great fundamental and technological significance and exists mostly in the manganites and a few other materials. Here we report colossal magnetoresistance that is starkly different from that in all other materials. The stoichiometric Mn3Si2Te6 is an insulator featuring a ferrimagnetic transition at 78 K. The resistivity drops by 7 orders of magnitude with an applied magnetic field above 9 Tesla, leading to an insulator-metal transition at up to 130 K. However, the colossal magnetoresistance occurs only when the magnetic field is applied along the magnetic hard a…
The features of electronic structure of La0.7Sr0.3MnO3, Pr0.8Sr0.2MnO3, and Pr0.6Sr0.4MnO3 polycrystalline films of different thickness have been investigated using magnetic circular dichroism (MCD) in the range of 1.1-4.2 eV. The temperature behavior of the samples electrical resistance were also has been studied. It was found that films with high Sr content (0.3 and 0.4) act as high-temperature semiconductors, while the maximum in the temperature dependences of these films resistivity indicates the transition of the samples to the metallic state at some temperature TM-S, which is different f…
Low frequency random telegraphic noise (RTN) and 1/f noise in the rare-earth manganite Pr$_{0.63}$Ca$_{0.37}$MnO$_3$ near the charge-ordering transition
本文研究了稀土钙钛矿锰氧化物Pr $_{0.63}$ Ca $_{0.37}$ MnO $_3$单晶的低频电阻涨落（噪声）。噪声测量是使用一个交流偏置和没有一个直流偏置电流施加在it. We发现，频谱功率$S_V(f)$包含两个组件-一个宽带1/f部分，存在于所有的频率和温度范围和一个单一的频率洛伦兹频率$f_c$这是强烈的温度依赖性。$S_V(f)$中的洛伦兹因随机电报噪声（RTN）而出现，如在波动的时间序列中所见，在$T_{CO}$周围的非常窄的温度窗口中看到，在那里它对波动做出了主要贡献。当所施加的直流偏置增加到超过某个阈值电流密度$J_{th}$时，电导变得非线性，并且人们看到由于RTN而在谱功率中出现显著的洛伦兹贡献。我们解释的RTN的外观，由于共存的电荷有序（CO）和反向轨道有序（ROO）的阶段，在动态平衡的介观长度尺度（$\approx 30nm$）和动力学控制的激活势垒$E_{a} ~ 0.45eV. The 1/f noise is low for $ T>> T_{CO} $ but increases by nearly two orders in a narrow temperature range as $ T_{CO} $接近从上面和概率分布函数（PDF）强烈偏离高斯。我们解释这种行为是由于与相关的波动，使PDF非高斯的电荷本地化的方法。
Dynamics of bi-stripes and a colossal metal-insulator transition in the bi-layer manganite La$_{2-2x}$Sr$_{1+2x}$Mn$_{2}$O$_{7}$ (x~0.59)
在相关电子材料中，电子通常自组织并形成各种具有电荷，自旋和轨道的潜在有序的图案，这些图案被认为与这些材料的许多新特性密切相关，包括超导性，金属-绝缘体转变和CMR效应。这些实空间模式如何影响材料的导电性和其他性质（通常在动量空间中描述）是现代凝聚态物理的主要挑战之一。此外，虽然静态条纹的存在是无可争议的，但在这种化合物中波动条纹的存在（和潜在影响）是一个有很大争议的话题。在这里，我们提出的电子激发La $_{2-2x}$ Sr $_{1+2x}$ Mn $_{2}$ O $_{7}$（x ~ 0.59）探测角分辨光电子能谱（ARPES），从中我们证明了一种新的类型的有序，称为双条纹，可以表现出静态或波动的顺序作为温度的函数。我们发现，静态的双条纹秩序是特别有害的电导率，完全本地化的双条纹区域的电子，而波动的条纹可以与移动载流子共存。这种物理学驱动了一种新的相变，其电导率随温度而发生巨大变化。我们的发现表明，量子条纹可以产生与静态对应物显著不同的电子特性。诱导它们之间的跃迁可以产生显著的电子现象，丰富了我们对相关电子系统的理解，并为电子器件的潜在应用打开了一扇窗户。
Electrical-transport characteristics of as-grown and oxygen-reduced La$_{0.7}$Ce$_{0.3}$MnO$_3$ films: calculation of hopping energies, Mn valences, and carrier localization lengths
目前，铈掺杂的LaMnO $_3$被生动地讨论为电子掺杂的对应原型，以充分建立的空穴掺杂的混合价锰氧化物。在此，比较在SrTiO $_3$单晶衬底上生长的不同厚度、CeO $_3$相分离程度和氧缺乏的La $_{0.7}$ Ce $_{0.3}$ MnO $_3$薄膜的电阻-相对电阻-相对电阻。从300~ 90 K的温度（R vs. T）行为。当薄膜厚度在10~ 100 nm范围内变化时，外延应变对电输运的影响很小，而CeO $_2$团簇的存在和氧的缺乏则完全改变了跳跃机制的类型.这是通过拟合各自的\textit{R-T}曲线与三种不同的传输模型（绝热极化子跳跃，莫特可变范围跳跃，埃夫罗斯-什克洛夫斯基可变范围跳跃），这是常用的混合价锰氧化物。几个特征的输运参数，如跳跃能量，载流子局域化长度，以及Mn价从拟合程序推导出来。
Colossal electroresistance (CER) in manganites, i.e., a large change in electrical resistance under the influence of either an applied electric field or an applied electric current, has often been described as complimentary to the colossal magnetoresistance (CMR) effect. Mixed valent vanadates with active t2g and empty eg orbitals, unlike manganites, have not naturally been discussed in this context, as double exchange based CMR is not realizable in them. However, presence of coupled spin and orbital degrees of freedom, metal-insulator transition (MIT) accompanied by orbital order-disorder tra…
