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Physics Express 2013, 3: 30
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Research Article
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Theoretical study of the interplay of spin-charge and orbital orderings in manganites
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Saswati Pandaa, P. Purohitb, G. C. Routc
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a Trident Academy of Technology, F2/A, Chandaka Industrial Estate, Bhubaneswar -751 024, India
b D. A. V. College, Titilagarh, Balangir, India
c Condensed Matter Physics Group, P. G. Department of Applied Physics and Ballistics, F. M. University, Balasore - 756 019, India
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Abstract |
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The doped rare-earth manganites exhibit a rich phase diagram due to several competing orders like charge, spin, orbital and lattice degrees of freedom. In order to study the complex properties of these systems, we report here a microscopic theoretical model. The model consists of band Jahn-Teller (JT) splitting in the eg band due to the orbital ordering and the charge density wave (CDW) in the same eg band arising due to the charge ordering for Mn3+ and Mn4+ ions. In addition to this we consider a double exchange model describing the spin-spin interaction among the eg and localized core t2g electrons. Due to Hund’s rule coupling, the core electrons provide strong ferromagnetism which aligns the eg spins ferromagnetically. Further, the model consists of Heisenberg type direct spin-spin interaction among the t2g core electrons. Thus the model provides a strong interplay among the JT distortion, charge-ordering and ferromagnetism in the conduction band and this finally gives rise to complex properties of the manganite system. It is observed that both the CDW coupling and the static JT coupling strongly change the CDW transition temperature and the lattice distortion temperature, while it enhances the magnitude of eg magnetization at low temperatures keeping the ferromagnetic transition temperature (Tc) unchanged due to strong Hund’s rule coupling. On the other hand, the double exchange coupling enhances ferromagnetic Curie temperature and also the magnitude of the induced magnetization in the eg electron band increases to a large extent. It is expected that this interplay will influence the magnetoresistance of the system as observed by the experiments. These results will be reported.
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Keywords |
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Colossal magneto-resistance; Jahn-Teller effect; Magnetization; Charge-density waves
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