Transport and magnetic anomalies due to A-site ionic-size mismatch in La0.5Ca0.5−xBaxMnO3

Mallik, R. ; Reddy, E. S. ; Paulose, P. L. ; Majumdar, Subham ; Sampathkumaran, E. V. (1999) Transport and magnetic anomalies due to A-site ionic-size mismatch in La0.5Ca0.5−xBaxMnO3 Journal of Physics: Condensed Matter, 11 (21). pp. 4179-4188. ISSN 0953-8984

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We present the results of measurements of the electrical resistivity (ρ), magnetoresistance (MR) and dc and ac susceptibility (χ) of polycrystalline samples of the type La0.5Ca0.5−xBaxMnO3, synthesized under identical heat-treatment conditions. The substitution of larger Ba ions for Ca results in a non-monotonic variation of the Curie temperature (TC) as the system evolves from a charge-ordered insulating state for x=0.0 to a ferromagnetic metallic state for x=0.5. An intermediate composition, that with x=0.1, interestingly exhibits ferromagnetic, insulating behaviour with thermal hysteresis in the ac χ at around the Curie temperature (TC=120 K). The x=0.2 and 0.3 compounds exhibit semiconducting-like behaviour as the temperature is lowered below 300 K, with a broad peak in ρ at around 80-100 K; these compositions exhibit a weak increase in ρ as the temperature is lowered below 30 K, indicative of electron localization effects; these compositions also undergo ferromagnetic transitions below about 200 and 235 K respectively, though these are non-hysteretic; most significantly, for these compositions, the MR is large and conveniently measurable over the entire temperature range of measurement below TC and this experimental finding may be of interest from the applications point of view. We infer that the A-site ionic-size mismatch plays a crucial role in determining these properties.

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Deposited On:29 Jun 2011 03:24
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