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      Colossal magnetoresistance in manganites as a multicritical phenomenon

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          Abstract

          The colossal magnetoresistance in manganites AMnO_3 is studied from the viewpoint of multicritical phenomena. To understand the complicated interplay of various phases, we study the Ginzburg-Landau theory in terms of both the mean-field approximation and the renormalization-group analysis to compare with the observed phase diagram. Several novel features, such as the first-order ferromagnetic transition, and the dip in the transition temperature near the multicritical point, can be understood as driven by enhanced fluctuations near the multicritical point. Furthermore, we obtain a universal scaling relation for the H/M-M^2 plot (Arrott plot), which fits rather well with the experimental data, providing the further evidence for the enhanced fluctuation.

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          Double Exchange Alone Does Not Explain the Resistivity of \(La_{1-x} Sr_x MnO_3\)

          The \(La_{1-x} Sr_x MnO_3\) system with \(0.2 \lesssim x \lesssim 0.4\) has traditionally been modelled with a ``double exchange'' Hamiltonian, in which it is assumed that the only relevant physics is the tendency of carrier hopping to line up neighboring spins. We present a solution of the double exchange model, show it is incompatible with many aspects of the resistivity data, and propose that a strong electron-phonon interaction arising from a Jahn-Teller splitting of the outer Mn d-level plays a crucial role.
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            Colossal Magnetoresistant Materials: The Key Role of Phase Separation

            The study of the manganese oxides, widely known as manganites, that exhibit the ``Colossal'' Magnetoresistance (CMR) 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. 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.
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              Percolative phase separation underlies colossal magnetoresistance in mixed-valent manganites

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                Author and article information

                Journal
                30 August 2002
                Article
                10.1103/PhysRevLett.90.197201
                cond-mat/0209002
                11c77648-b09a-4954-ac63-39deb48475f2
                History
                Custom metadata
                Phys. Rev. Lett. 90, 197201 (2003)
                4 pages, 3 figures
                cond-mat.str-el

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