Topic
Colossal magnetoresistance
About: Colossal magnetoresistance is a research topic. Over the lifetime, 3658 publications have been published within this topic receiving 130104 citations.
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TL;DR: An unusual coexistence of the CO/OO and FM metallic states with micrometer size below a MI transition temperature of 60 K is found, providing direct evidence of the phase separation found in CMR manganites.
Abstract: Magnetic domain structure in manganites was investigated by Lorentz electron microscopy, in order to understand some unusual physical properties, such as a colossal magnetoresistance (CMR) effect and a metal-to-insulator (MI) transition. In particular, we examined the spatial distribution of the charge/orbital ordered (CO/OO) insulator state and the ferromagnetic (FM) metallic state in phase-separated manganites, (La 5 / 8 - x Pr x )Ca 3 / 8 MnO 3 for x = 0.375, by obtaining both the dark-field and Lorentz images. We found an unusual coexistence of the CO/OO and FM metallic states with micrometer size below a MI transition temperature of 60 K. Our experimental findings provide direct evidence of the phase separation found in CMR manganites.
22 citations
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TL;DR: In this paper, the temperature dependence of the magnetoresistance for Co/Ru/Co sandwiches and superlattices has been investigated and it was found that the magnetorsistance is strongly dependent on the temperature and oscillates as a function of Ru thickness with different shape and phase of oscillation between RT and 4.2 K. This was attributed to the existence of a large mixed CoRu diluted region at the interfaces, the magnetism of which shows a strong dependence on temperature.
21 citations
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TL;DR: In this paper, the extrinsic properties of La 0.7 Ca 0.3 MnO y samples and their relation with the microstructural configuration were investigated using X-ray diffraction associated with Rietveld refinement, scanning electron microscopy and AC magnetic susceptibility measurements.
21 citations
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TL;DR: Magnetoresistance is observed in nonferromagnetic oxides containing FeIV which have magnetic behaviour characteristic of small magnetic clusters as mentioned in this paper, and magnetic properties characteristic of magnetic cliques.
21 citations
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TL;DR: In this paper, an extension to include long-range Coulomb interactions of a quantum two-fluid l-b model for manganites has been proposed, which leads to an excellent description of such inhomogeneities.
Abstract: Electronic, magnetic, or structural inhomogeneities ranging in size from nanoscopic to mesoscopic scales seem endemic and are possibly generic to colossal magnetoresistance manganites and other transition metal oxides. They are hence of great current interest and understanding them is of fundamental importance. We show here that an extension, to include long-range Coulomb interactions, of a quantum two-fluid l-b model proposed recently for manganites [Phys. Rev. Lett. 92, 157203 (2004)] leads to an excellent description of such inhomogeneities. In the l-b model two very different kinds of electronic states, one localized and polaronic (l) and the other extended or broad band (b) coexist. For model parameters appropriate to manganites and even within a simple dynamical mean-field theory (DMFT) framework, it describes many of the unusual phenomena seen in manganites, including colossal magnetoresistance (CMR), qualitatively and quantitatively. However, in the absence of long-ranged Coulomb interaction, a system described by such a model would actually phase separate, into macroscopic regions of l and b electrons, respectively. As we show in this paper, in the presence of Coulomb interactions, the macroscopic phase separation gets suppressed and instead nanometer scale regions of polarons interspersed with band electron puddles appear, constituting a kind of quantum Coulomb glass. We characterize the size scales and distribution of the inhomogeneity using computer simulations. For realistic values of the long-range Coulomb interaction parameter V-0, our results for the thresholds for occupancy of the b states are in agreement with, and hence support, the earlier approach mentioned above based on a configuration averaged DMFT treatment which neglects V-0; but the present work has features that cannot be addressed in the DMFT framework. Our work points to an interplay of strong correlations, long-range Coulomb interaction, and dopant ion disorder, all inevitably present in transition metal oxides as the origin of nanoscale inhomogeneities rather than disorder frustrated phase competition as is generally believed. As regards manganites, it argues against explanations for CMR based on disorder frustrated phase separation and for an intrinsic origin of CMR. Based on this, we argue that the observed micrometer (meso) scale inhomogeneities owe their existence to extrinsic causes, e.g., strain due to cracks and defects. We suggest possible experiments to validate our speculation.
21 citations