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Effects of Zn substitution on the magnetic and transport properties of $La_{0.6}Sr_{0.4}Mn_{1-y}Zn_yO_{3-\delta}(0\leq y\leq 0.3)$

Vijayanandhini, K and Kutty, TRN (2007) Effects of Zn substitution on the magnetic and transport properties of $La_{0.6}Sr_{0.4}Mn_{1-y}Zn_yO_{3-\delta}(0\leq y\leq 0.3)$. In: Solid State Communications, 141 (5). pp. 252-257.

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Abstract

Phase-singular solid solutions of $La_{0.6}Sr_{0.4}Mn_{1-y}ZnyO_{3-\delta}(0\leq y\leq 0.3)$ [LSMZO] perovskite of rhombohedral symmetry (space group: R3c) with y up to 30 at.% could be synthesized notwithstanding the differences in ionic radii of $Mn_{VI}^{3+}$ (i.r. = 0.645 \AA ) and $Zn^{2+}_{VI}$(i.r. = 0.74 \AA ). The $LSMZO \leq 02$ compositions are ferromagnetic metallic (FMM) at room temperature whereas LSMZO-02–08 are ferromagnetic insulators (FMI) and LSMZO > 08 are paramagnetic insulators (PMI). Total obliteration of the FM transition is unique to Zn-doping at y > 8 at.% leading to PMI even at low temperatures, measured up to 8 K (presently). The FM to PM transition $(T_c)$ and the peak $(T_p)$ in resistivity–temperature curves decreases with the Zn-content. The charge-transport in p-type LSMZO is predictable by variable range hopping (VRH), which changes to nearest-neighbor hopping of small polarons (NNHP) at $T > T_p$. Non-stoichiometry (0.005\leq\delta\leq 0.21) evaluated chemically from redox titrations indicated the prevalence of excess oxygen vacancy $(V_O)$ rather than charge compensatively predictable values which, in turn, indicates the diminishing $Mn^{4+}$ content in LSMZO. The $V_O$’s act as electron donors in p-LSMZO and this increases the resistivity $(\rho RT)$ associated with the shift in $T_c$ to low temperatures. Increased $\rho RT$ on annealing in low $p_{o2}$ is a clear evidence on the role of $V_O$ in LSMZO.

Item Type: Journal Article
Additional Information: Copyright of this article belongs to Elsevier.
Keywords: A. La0.6Sr0.4MnO3;D. Polaron localizations;D. Charge compensation;D. Ferromagnetic-insulator
Department/Centre: Division of Chemical Sciences > Materials Research Centre
Date Deposited: 23 Mar 2007
Last Modified: 19 Sep 2010 04:35
URI: http://eprints.iisc.ernet.in/id/eprint/9959

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