Evidence of spin transition and charge order in cobalt substituted La0.7Ca0.3MnO3

Abstract

The transport and magnetic studies of a series of compounds having the generalformula La0.7Ca0.3Mn1−xCoxO3 (0.1 ≤ x < 0.9) have shown thatCo3+can exist both in high spin and low spin states (diamagnetic state). This is foundto affect greatly the transport and magnetic properties of the systemat low temperature by varying the strengths of both double-exchange(DE) and superexchange (SE) interactions. The introduction of cobaltchanges the mobile carrier concentration, so even with 10% of Coconcentration the strength of DE is found to decrease considerably. For x ≥ 0.25there is a clear spin transition at low temperature from the high tothe low spin state of trivalent cobalt and this leads to change inferromagnetic (FM) and antiferromagnetic (AFM) phases. For x ≥ 0.25 there are twotransitions for each value of x:the upper one gives the FM and AFM spin arrangement depending uponwhether the DE or the SE dominates; the lower one is obtained due to thetransition from the high to the low spin state of the trivalent cobalt ion.