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Colossal magnetoresistance of oxide spinels, $Co_{x}Mn_{3-x}O_{4}$

Philip, John and Kutty, TRN (1999) Colossal magnetoresistance of oxide spinels, $Co_{x}Mn_{3-x}O_{4}$. In: Materials Letters, 39 (6). pp. 311-317.

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CoxMn3-xO4 (x = 0.6 to 2) spinels exhibit a transition between para- to ferrimagnetic phase below 200 K. This transition is accompanied by a change in slope of the electrical resistance from negative to positive temperature coefficient (NTC to PTC) although associated with large resistivity of similar to 10(9) Omega cm. Under the external magnetic field, the electrical resistivity decreases by more than one order of magnitude around the transition temperature. The magnetoresistance (MR) coefficient maximizes around 0.8. The resistivity ratio, rho/rho(H = 0), does not saturate with magnetic field, confirming that the large MR is the result of colossal magnetoresistance (CMR). Doping with Li or Cu decreases the room temperature resistivity as a result of the increase in hole concentration. However, Cu decreases the MR because addition of copper ions reduces the exchange interactions. Analyses of the complex impedance spectra show that the grain boundary resistance R-gb increases with decrease in temperature and the large resistivity may be due to the trapping of charge carriers by the oxygen vacancies. Charge trapping at the defect centres is also indicated from the variable maximum in the rho-T curves of the same specimen (x = 0.6) annealed in different p(O2) at elevated temperatures. (C) 1999 Elsevier Science B.V. All rights reserved.

Item Type: Journal Article
Publication: Materials Letters
Publisher: Elsevier Science BV
Additional Information: Copyright of this article belongs to Elsevier Science BV.
Keywords: Colossal magnetoresistance;NTC to PTC transition;Cobalt manganite spinels;Charge trapping.
Department/Centre: Division of Chemical Sciences > Materials Research Centre
Date Deposited: 02 Mar 2009 06:20
Last Modified: 19 Sep 2010 05:00
URI: http://eprints.iisc.ac.in/id/eprint/18096

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