SPIN-ORBITAL ORDERING AND GIANT MAGNETORESISTANCE IN COBALT OXIDES: INTRINSIC MAGNETIC-FIELD-EFFECT TRANSISTOR
Layered cobalt oxides RBaCo2O5+x (R is a rare-earth element) possess very rich phase diagrams owing to the competition of various spin-charge-orbital ordered states in the doped square-lattice CoO2 planes. To clarify the mechanism of the giant magnetoresistance (GMR) that accompanies magnetic transformations in these compounds we have prepared and studied GdBaCo2O5+x single crystals with precisely tuned doping levels. We .nd that the GMR is observed even in the parent composition (x = 0.50) with all cobalt ions in the Co3+ state, which has neither phase segregation nor charge ordering that are responsible for the MR in manganites. A new MR mechanism is suggested for these cobalt oxides where the charge carrier generation in conducting channels is controlled by the magnetic state of their local environment.
KeywordsAnisotropy Cobalt Lanthanum Manganite
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