Percolative phase separation underlies colossal magnetoresistance in mixed-valent manganites

Uehara, M.; Mori, Shigeo; Chen, C. H.; Cheong, Sang‐Wook

doi:10.1038/21142

Cited by 1,736 publications

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“…This makes an accurate determination of δ in the bulk of the film difficult. Like other colossal magnetoresistive manganites 5,6 , bulk stoichiometric LPCMO exhibits a paramagnetic to ferromagnetic transition concomitant with a MIT at a transition temperature of 120 K [32][33][34] . Both tensile strain 23,35 and the introduction of oxygen vacancies shift the MIT to lower temperatures 7 , the former through a stabilization of the charge ordered (Jahn-Teller distorted) state at the expense of the ferromagnetic metallic state 35 , and the latter through a direct structural disruption of the ferromagnetic double exchange interaction, essentially destroying the domain structure of LPCMO 7 .…”

Section: Resultsmentioning

confidence: 96%

A persistent metal–insulator transition at the surface of an oxygen-deficient, epitaxial manganite film

et al. 2013

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The oxygen stoichiometry has a large influence on the physical and chemical properties of complex oxides. Most of the functionality in e.g. catalysis and electrochemistry depends in particular on control of the oxygen stoichiometry. In order to understand the fundamental properties of intrinsic surfaces of oxygen-deficient complex oxides, we report on in situ temperature dependent scanning tunnelling spectroscopy experiments on pristine oxygen deficient, epitaxial manganite films. Although these films are insulating in subsequent ex situ in-plane electronic transport experiments at all temperatures, in situ scanning tunnelling spectroscopic data reveal that the surface of these films exhibits a metalinsulator transition (MIT) at 120 K, coincident with the onset of ferromagnetic ordering of small clusters in the bulk of the oxygen-deficient film. The surprising proximity of the surface MIT transition temperature of nonstoichiometric films with that of the fully oxygenated bulk suggests that the electronic properties in the surface region are not significantly affected by oxygen deficiency in the bulk. This carries important implications for the understanding and functional design of complex oxides and their interfaces with specific electronic properties for catalysis, oxide electronics and electrochemistry.In catalysis and electrochemistry the surface properties of catalyst and electrode materials dominate their functional performance. For oxide materials this is often associated with the bulk oxygen stoichiometry, with oxygen vacancies frequently improving the catalytic and electrochemical performance 1, 2 . This contrasts with the spectacular physical properties with promising functionality displayed by complex oxides such as perovskites [3][4][5][6] but that are generally strongly reduced or even eliminated by the introduction of oxygen vacancies 7 . Moreover, in nanoscale oxide heterostructures the possible large chemical and electrostatic potential gradients, and the high surface/volume ratios may drastically affect the properties of the material 8 . With respect to the chemically important surface properties, it is currently not clear whether an oxygen deficiency in the bulk of a three-dimensional (3D) perovskite affects these surface properties in concert with those of the bulk, or whether this is significantly different due to eg. altered oxygen vacancy formation energies near the surface due to different local ionic coordination or even a different local stoichiometry of the unit cells at the surface and interface. Complicating our understanding of the electronic properties of catalytically relevant complex oxide surfaces is the fact that at their surfaces and interfaces the broken translational symmetry fundamentally changes the properties 9, 10 . While this has been shown to produce remarkable physics at interfaces [11][12][13] , at surfaces of three-dimensional (3D) perovskites the results are qualitatively different: many fully oxygenated 3D perovskite surfaces and interfaces exhibit a so-cal...

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Section: Resultsmentioning

confidence: 96%

A persistent metal–insulator transition at the surface of an oxygen-deficient, epitaxial manganite film

et al. 2013

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“…One of the most interesting properties of these materials is the spontaneous phase separation between different electronic/magnetic states 1,3 . This sort of phase separation is a common characteristic of many correlated electron oxides, originating from the strong coupling between lattice, charge, orbital and spin degrees of freedom.…”

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“…This sort of phase separation is a common characteristic of many correlated electron oxides, originating from the strong coupling between lattice, charge, orbital and spin degrees of freedom. The electronic phase separation has been revealed at first by magnetic and electrictransport characterization and verified consequently by a variety of structural probes, such as X-ray and neutron diffraction measurements [3][4][5] . Recently, studies using microscopies have provided us with the real space image of phase separation in correlated electron oxides 3,6 .…”

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confidence: 99%

“…The electronic phase separation has been revealed at first by magnetic and electrictransport characterization and verified consequently by a variety of structural probes, such as X-ray and neutron diffraction measurements [3][4][5] . Recently, studies using microscopies have provided us with the real space image of phase separation in correlated electron oxides 3,6 . Nevertheless, knowledge of dynamic transport in multiple phases is lacking up to now, although it is quite important both for understanding of underlying physics as well as promising applications 1 .…”

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“…Nevertheless, knowledge of dynamic transport in multiple phases is lacking up to now, although it is quite important both for understanding of underlying physics as well as promising applications 1 . It has been revealed that the microscopic phases have linear dimensions on the order of ten to several hundred nanometres and are distributed over the system almost randomly [3][4][5] . The small size and random distribution of multiple phases obstruct us to explore them separately in detail.…”

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Dynamics of multiple phases in a colossal-magnetoresistive manganite as revealed by dielectric spectroscopy

et al. 2012

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Electronic phase separation is one of the key features in correlated electron oxides. The coexistence and competition of multiple phases give rise to gigantic responses to tiny stimuli producing dramatic changes in magnetic, transport and other properties of these compounds. To probe the physical properties of each phase separately is crucial for a comprehensive understanding of phase separation phenomena and for designing their device functions. Here we unravel, using a unique p-n junction configuration, dynamic properties of multiple phases in manganite thin films. The multiple dielectric relaxations have been detected and their corresponding multiple phases have been identified, while the activation energies of dielectric responses from different phases were extracted separately. Their phase evolutions with changing both temperature and applied magnetic field have been demonstrated by dielectric response. These results provide a guideline for exploring the electronic phase separation phenomena in correlated electron oxides.

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Colossal Magnetoresistive Materials

Maignan

2002

Encyclopedia of Smart Materials

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Magnetoresistance (MR) is defined as the relative change in the electrical resistivity of a material upon the application of a magnetic field. MR is positive for most nonmagnetic metals, and its magnitude is limited to a few percent, whereas MR can be negative in magnetic materials because the magnetic field tends to reduce the spin disorder. MR is of considerable technological interest. IBM is using the Permalloy (composition: 80% Ni and 20% Fe) MR of about 3% in a small magnetic field at room temperature for the magnetic storage of information. More recently, larger magnetoresistance also called giant MR (GMR) was observed in thin films of magnetic superlattices (for instance, Fe, Cr) for which metallic layers of a ferromagnet and a nonmagnetic material (or an antiferromagnet) are alternately deposited on a substrate. By doing so, the MR magnitude is increased by an order of magnitude. Small ferromagnetic particles deposited on a paramagnetic thin film also provide an alternative way to obtain GMR devices. For both material classes, small magnetic field applications (a few oersteds) are sufficient to align the magnetizations ferromagnetically and thus to induce a resistivity decrease originating in decreased scattering. In hole‐doped perovskite manganites magnetoresistance values of ∼ −100% in large magnetic fields (several teslas) have been discovered. These effects are called CMR to distinguish them from GMR. CMR has motivated a large number of experimental studies of these oxides in bulk (ceramics and crystals) and in thin films and also of theoretical work to understand the origin of the phenomenon. In this article, several representative examples of perovskite manganites are given to illustrate the richness of their phase diagrams. More particularly, the chemical key factor governing the CMR of hole‐doped manganites that contain 30% Mn 4 + and have the Ln 0.7 AE 0.3 MnO 3 formula are reviewed. The existence of Mn 3 + /Mn 4 + charge ordering in the Mn lattice for half‐doped manganites and also for Mn 4 + }‐rich compositions (electron‐doped, x > 0.5) are discussed. Finally, the possibility of obtaining CMR properties in Mn 4 + ‐rich manganites is shown.

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Percolative phase separation underlies colossal magnetoresistance in mixed-valent manganites

Cited by 1,736 publications

References 30 publications

A persistent metal–insulator transition at the surface of an oxygen-deficient, epitaxial manganite film

A persistent metal–insulator transition at the surface of an oxygen-deficient, epitaxial manganite film

Dynamics of multiple phases in a colossal-magnetoresistive manganite as revealed by dielectric spectroscopy

Colossal Magnetoresistive Materials

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