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High temperature susceptibility in electron doped Ca1-xYxMnO3: Double Exchange vs Superexchange

H. Aliaga·M. T. Causa·M. Tovar·A. Butera·B. Alascio·D. Vega·G. Leyva·G. Polla·P. Konig
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Abstract

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, c(T), follows a Curie-Weiss (CW) law only for T > 450 K and, below this temperature, c^-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 c(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 analyzed the problem through Montecarlo 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 c^-1(T) for x<=0.1.

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H. Aliaga, M. T. Causa, M. Tovar, A. Butera, B. Alascio, D. Vega, G. Leyva, G. Polla, P. Konig. 2002-11-12. High temperature susceptibility in electron doped Ca1-xYxMnO3: Double Exchange vs Superexchange. https://doi.org/10.1088/0953-8984%2F15%2F2%2F324

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