Interaction between the d -Shells in the Transition Metals. II. Ferromagnetic Compounds of Manganese with Perovskite Structure
TL;DR: In this paper, it was shown that both electrical conduction and ferromagnetic coupling in these compounds arise from a double exchange process, and a quantitative relation was developed between electrical conductivity and the Ferromagnetic Curie temperature.
Abstract: Recently, Jonker and Van Santen have found an empirical correlation between electrical conduction and ferromagnetism in certain compounds of manganese with perovskite structure. This observed correlation is herein interpreted in terms of those principles governing the interaction of the $d$-shells of the transition metals which were enunciated in the first paper of this series. Both electrical conduction and ferromagnetic coupling in these compounds are found to arise from a double exchange process, and a quantitative relation is developed between electrical conductivity and the ferromagnetic Curie temperature.
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TL;DR: A negative isotropic magnetoresistance effect has been observed in thin oxide films of perovskite-like La0.67Ca0.33MnOx, which could be useful for various magnetic and electric device applications if the observed effects of material processing are optimized.
Abstract: A negative isotropic magnetoresistance effect more than three orders of magnitude larger than the typical giant magnetoresistance of some superlattice films has been observed in thin oxide films of perovskite-like La0.67Ca0.33MnOx. Epitaxial films that are grown on LaAIO3 substrates by laser ablation and suitably heat treated exhibit magnetoresistance values as high as 127,000 percent near 77 kelvin and ∼1300 percent near room temperature. Such a phenomenon could be useful for various magnetic and electric device applications if the observed effects of material processing are optimized. Possible mechanisms for the observed effect are discussed.
4,079 citations
TL;DR: In this paper, a large variety of experiments reviewed in detail here contain results compatible with the theoretical predictions, including phase diagrams of manganite models, the stabilization of the charge/orbital/spin ordered half-doped correlated electronics (CE)-states, the importance of the naively small Heisenberg coupling among localized spins, the setup of accurate mean-field approximations, and the existence of a new temperature scale T∗ where clusters start forming above the Curie temperature, the presence of stripes in the system, and many others.
2,927 citations
Cites background or result from "Interaction between the d -Shells i..."
...Originally, Zener (1951b) considered the explicit movement of electrons schematically written (Cieplak, 1978) as Mn t O t s Mn P Mn O t s Mn t where 1, 2, and 3 label electrons that belong either to the oxygen between manganese, or to the e -level of the Mn-ions....
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...Actually, the FM phases recently generated in computer simulations and a variety of mean-"eld approximations resemble more closely the predictions of another work of Zener (1951a), where indeed a large Hund coupling is invoked as the main reason for ferromagnetism in some compounds....
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...Usually, an extra simpli"cation is carried out by neglecting the orbital degrees of freedom, leading to the FM Kondo model or one-orbital double-exchange model, which will be simply referred as the `one-orbital modela hereafter, given as (Zener, 1951b; Furukawa, 1994) H "!t i j (a i aj #h.c.)!...
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...The states of manganites were assumed to be uniform, and `double exchangea (DE) was proposed by Zener (1951b) as a way to allow for charge to move in manganites by the generation of a spin polarized state....
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...However, there is little resemble of these models and physical process with the original DE ideas (Zener, 1951b) where two electrons were involved in the actual hopping....
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TL;DR: A hybrid light-emitting diode (LED) that combines the ease of processability of organic materials with the narrow-band, efficient luminescence of colloidal quantum dots (QDs) is demonstrated and a 25-fold improvement in luminescent efficiency is observed.
Abstract: The integration of organic and inorganic materials at the nanometre scale into hybrid optoelectronic structures enables active devices that combine the diversity of organic materials with the high-performance electronic and optical properties of inorganic nanocrystals. The optimization of such hybrid devices ultimately depends upon the precise positioning of the functionally distinct materials. Previous studies have already emphasized that this is a challenge, owing to the lack of well-developed nanometre-scale fabrication techniques. Here we demonstrate a hybrid light-emitting diode (LED) that combines the ease of processability of organic materials with the narrow-band, efficient luminescence of colloidal quantum dots (QDs). To isolate the luminescence processes from charge conduction, we fabricate a quantum-dot LED (QD-LED) that contains only a single monolayer of QDs, sandwiched between two organic thin films. This is achieved by a method that uses material phase segregation between the QD aliphatic capping groups and the aromatic organic materials. In our devices, where QDs function exclusively as lumophores, we observe a 25-fold improvement in luminescence efficiency (1.6 cd A(-1) at 2,000 cd m(-2)) over the best previous QD-LED results. The reproducibility and precision of our phase-segregation approach suggests that this technique could be widely applicable to the fabrication of other hybrid organic/inorganic devices.
2,438 citations
TL;DR: In this article, a review is concerned with the neglected class of inorganic compounds, which contain ions of the same element in two different formal states of oxidation, and a number of references cite that many individual examples of this class have been studied, yet they have very rarely been treated as a class, and there has never before, to our knowledge, been a systematic attempt to classify their properties in terms of their electronic and molecular structures.
Abstract: Publisher Summary This review is concerned with the neglected class of inorganic compounds, which contain ions of the same element in two different formal states of oxidation. Although the number of references cited in our review show that many individual examples of this class have been studied, yet they have very rarely been treated as a class, and there has never before, to our knowledge, been a systematic attempt to classify their properties in terms of their electronic and molecular structures. In the past, systems containing an element in two different states of oxidation have gone by various names, the terms “mixed valence,” nonintegral valence,” “mixed oxidation,” “oscillating valency,” and “controlled valency” being used interchangeably. Actually, none of these is completely accurate or all-embracing, but in our hope to avoid the introduction of yet another definition, we have somewhat arbitrarily adopted the phrase “mixed valence” for the description of these systems. The concept of resonance among various valence bond structures is one of the cornerstones of modern organic chemistry.
2,208 citations
TL;DR: An overview is given here on this "orbital physics," which will be a key concept for the science and technology of correlated electrons.
Abstract: An electron in a solid, that is, bound to or nearly localized on the specific atomic site, has three attributes: charge, spin, and orbital. The orbital represents the shape of the electron cloud in solid. In transition-metal oxides with anisotropic-shaped d-orbital electrons, the Coulomb interaction between the electrons (strong electron correlation effect) is of importance for understanding their metal-insulator transitions and properties such as high-temperature superconductivity and colossal magnetoresistance. The orbital degree of freedom occasionally plays an important role in these phenomena, and its correlation and/or order-disorder transition causes a variety of phenomena through strong coupling with charge, spin, and lattice dynamics. An overview is given here on this "orbital physics," which will be a key concept for the science and technology of correlated electrons.
1,916 citations