Electrical transport properties and magnetoresistance of $LaMn_{1-x}M_xO_{3+\delta}$ substituted with diamagnetic ions (M = Li,Mg, Ti)

Kutty, TRN and Philip, John (2000) Electrical transport properties and magnetoresistance of $LaMn_{1-x}M_xO_{3+\delta}$ substituted with diamagnetic ions (M = Li,Mg, Ti). In: Journal of Physics: Condensed Matter, 12 (35). pp. 7747-7758.

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Abstract

Substitution of aliovalent diamagnetic ions with fixed valence states $(Li^+, Mg^{2+} and Ti^{4+})$ at the Mn site in $LaMnO_3$ $(LaMn_{1-x}M_xO_{3+\delta})$ drastically decreases the room temperature resistivity (from ~368 to ~10$\Omega$ cm). The concentration of $Mn^{4+}$ ions increases with increase in diamagnetic addition. The presence of diamagnetic ions in $LaMnO_3$ samples shows low values of \delta (0–0.045) in comparison to $LaMnO_{3+\delta}$ (\delta= 0–0.26). Therefore, the cation vacancies (La, Mn) in the La and Mn sublattices will be much lower than that of $LaMnO_{3+\delta}$ ; consequently the scattering of holes at the vacancies will be reduced, resulting in lower resistivity. There is no transition to metallic state at low temperatures even for samples with large hole concentration as in the case of $LaMn_{0.8}Mg_{0.2}O_{3+\delta}$ . However, there is a transition from the para- to ferromagnetic state. In resistivity characteristics, the high temperature region satisfies the small polaron model and the activation energy calculated is less than 0.3 eV. Thermopower measurements exhibit a change in behaviour at low temperatures, which is not observed in resistivity curves. Magnesium added samples $(LaMn_{0.8}Mg_{0.2}O_{3+\delta})$ show a large negative magnetoresistance (MR) coefficient (0.8) at low magnetic fields (H = 1 T) and the MR increases with Mg concentration (x = 0.05–0.2).Samples treated at low partial pressures of oxygen at 1050–1300 K display large variation in resistivity and MR due to the reduction in holes.

Item Type:	Journal Article
Publication:	Journal of Physics: Condensed Matter
Publisher:	Institute of Physics
Additional Information:	Copyright of this article belongs to Institute of Physics.
Department/Centre:	Division of Chemical Sciences > Materials Research Centre
Date Deposited:	25 Aug 2006
Last Modified:	19 Sep 2010 04:30
URI:	http://eprints.iisc.ac.in/id/eprint/8101

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