Manganite

About: Manganite is a research topic. Over the lifetime, 3430 publications have been published within this topic receiving 60353 citations.

Interaction between the d -Shells in the Transition Metals. II. Ferromagnetic Compounds of Manganese with Perovskite Structure

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.

Colossal Magnetoresistant Materials: The Key Role of Phase Separation

Abstract: The study of the manganese oxides, widely known as manganites, that exhibit the “colossal” magnetoresistance effect is among the main areas of research within the area of strongly correlated electrons. After considerable theoretical effort in recent years, mainly guided by computational and mean-field studies of realistic models, considerable progress has been achieved in understanding the curious properties of these compounds. These recent studies suggest that the ground states of manganite models tend to be intrinsically inhomogeneous due to the presence of strong tendencies toward phase separation, typically involving ferromagnetic metallic and antiferromagnetic charge and orbital ordered insulating domains. Calculations of the resistivity versus temperature using mixed states lead to a good agreement with experiments. The mixed-phase tendencies have two origins: (i) electronic phase separation between phases with different densities that lead to nanometer scale coexisting clusters, and (ii) disorder-induced phase separation with percolative characteristics between equal-density phases, driven by disorder near first-order metal–insulator transitions. The coexisting clusters in the latter can be as large as a micrometer in size. It is argued that a large variety of experiments reviewed in detail here contain results compatible with the theoretical predictions. The main phenomenology of mixed-phase states appears to be independent of the fine details of the model employed, since the microscopic origin of the competing phases does not influence the results at the phenomenological level. However, it is quite important to clarify the electronic properties of the various manganite phases based on microscopic Hamiltonians, including strong electron–phonon Jahn–Teller and/or Coulomb interactions. Thus, several issues are discussed here from the microscopic viewpoint as well, including the 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, 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. However, much work remains to be carried out, and a list of open questions is included here. It is also argued that the mixed-phase phenomenology of manganites may appear in a large variety of compounds as well, including ruthenates, diluted magnetic semiconductors, and others. It is concluded that manganites reveal such a wide variety of interesting physical phenomena that their detailed study is quite important for progress in the field of correlated electrons.

CMR manganites: physics, thin films and devices

Abstract: The manganese oxides of general formula RE1−xMxMnO3 (RE = rare earth, M = Ca, Sr, Ba, Pb) have remarkable interrelated structural, magnetic and transport properties induced by the mixed valence (3+–4+) of the Mn ions. In particular, they exhibit very large negative magnetoresistance, called colossal magnetoresistance (CMR), in the vicinity of metal–insulator transition for certain compositions. In this review paper, we summarize the most important features of the physics of the CMR manganites. The growth techniques for manganese oxide thin films, which are the basic material for potential applications, are reviewed and their structure and morphology examined in relation to growth parameters. The effects of epitaxial strains on the physical properties are discussed. Early works on superlattices and devices are presented.

Room temperature spin polarized injection in organic semiconductor

Abstract: Spintronics is a new branch of electronics based on purely quantum effects. Instead of carrier charge transfer, as in usual electronics, it evokes carrier's spin transfer. The search of new materials suitable for injecting and transferring carriers with a preferential spin orientation is of paramount importance for the development of spintronics. Here we report a first experimental evidence of room temperature direct spin polarized injection in sexithienyl (T 6 ), a prototypical organic semiconductor, from colossal magnetoresistance manganite La 0.7 Sr 0.3 MnO 3 (LSMO). A strong magnetoresistance (up to 30%) was measured on nanostructured planar hybrid junctions LSMO/T 6 /LSMO. The spin diffusion length in T 6 is about 200 nm at room temperature. The results are discussed taking into account possible spin-flip mechanisms in organic material and interface effects.

Large magnetoresistance in non-magnetic silver chalcogenides

Abstract: Several materials have been identified over the past few years as promising candidates for the development of new generations of magnetoresistive devices. These range from artificially engineered magnetic multilayers' and granular alloys, in which the magnetic-field response of interfacial spins modulates electron transport to give rise to 'giant' magnetoresistance, to the manganite peravskites, in which metal-insulator transitions driven by a magnetic field give rise to a `colossal' magnetoresistive response (albeit at very high fields). Here we describe a hitherto unexplored class of magnetoresistive compounds, the silver chalcogenides. At high temperatures, the compounds Ag_2S, Ag_2Se and Ag_2Te are superionic conductors; below similar to 400 K, ion migration is effectively frozen and the compounds are non-magnetic semiconductors that exhibit no appreciable magnetoresistance. We show that slightly altering the stoichiometry can lead to a marked increase in the magnetic response. At room temperature and in a magnetic field of similar to 55 kOe, Ag_(2+δ)Se and Ag_(2+δ)Te show resistance increases of up to 200%, which are comparable with the colossal-magnetoresistance materials. Moreover, the resistance of our most responsive samples exhibits an unusual linear dependence on magnetic field, indicating both a potentially useful response down to fields of practical importance and a peculiarly long length scale associated with the underlying mechanism.