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artículo con referato
"High Temperature Susceptibility in Electron Doped Ca1-xYxMnO3: Double Exchange versus Superexchange"
H. Aliaga, M.T. Causa, M. Tovar, A. Butera, B. Alascio, D. Vega, A.G. Leyva, G. Polla and P. Konig
J. Phys.: Condens. Matter 15(2) (2003) 249-258
We present a study of the magnetic properties of the electron doped manganites Ca1-xYxMnO3 (for 0 ≤ x ≤ 0.25) in the paramagnetic regime. For the less doped samples (x ≤ 0.1) the magnetic susceptibility, χ(T), follows a Curie-Weiss (CW) law only for T > 450 K and, below this temperature, χ-1(T) shows a ferrimagnetic-like curvature. We approached the discussion of these results in terms of a simple mean-field model where double exchange, approximated by a ferromagnetic Heisenberg-like interaction between Mn3+ and Mn4+ ions, competes with classical superexchange. For higher levels of doping (x ≤ 0.15), the CW behaviour is observed down to the magnetic ordering temperature (Tmo) and a better description of χ(T) was obtained by assuming full delocalization of the eg electrons. In order to explore the degree of delocalization as a function of T and x, we analysed the problem through Monte Carlo simulations. Within this picture we found that at high T the electrons doped are completely delocalized but, when Tmo is approached, they form magnetic polarons of large spin that cause the observed curvature in χ-1(T) for x ≤ 0.1.
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