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Abstract: Rare earth perovskite cobaltites are increasingly recognized as materials ofimportance due to rich physics and chemistry in their ordered-disorderedstructure for the same composition. Apart from colossal magnetoresistanceeffect, like manganites, the different forms of cobaltites exhibit interestingphenomena including spin, charge and orbital ordering, electronic phaseseparation, insulator-metal transition, large thermoelectric power at lowtemperature. Moreover, the cobaltites which display colossal magnetoresistanceeffect could be used as read heads in magnetic data storage and also in otherapplications depending upon their particular properties. The A-siteordereddisordered cobaltites exhibit ferromagnetism and metal-insulatortransitions as well as other properties depending on the composition, size ofA-site cations and various external factors such as pressure, temperature,magnetic field etc. Ordered cobaltites, having a 112-type layered structure,are also reported to have an effectively stronger electron coupling due tolayered A-site cationic ordering. Most importantly for the present article wefocus on La-Ba-Co-O based ordered-disordered perovskite phases, which exhibitinteresting magnetic and electron transport properties with ferromagnetictransition, TC ~ 177K, and it being the first member of lanthanide series.Zener double exchange mechanism considered to be crucial for understandingbasic physics of the ferromagneticmetallic phase, yet does not explain clearlythe insulating-type phase. In terms of electron transport theferromagnetic-metallic or insulating-semiconducting states have been discussedin the present article with different types of hopping model.



Author: Asish K. Kundu, B. Raveau

Source: https://arxiv.org/







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