Magnetic properties of pseudo-ideal cubic La0.6−xCaxBa0.4CoO3 with hole doping

Abstract

The La0.6−xCaxBa0.4CoO3 (x=0.03, 0.04, 0.05, 0.075, 0.1 and 0.15) compounds are synthesized. The cubic La0.6Ba0.4CoO3 has the strongest ferromagnetic (FM) double exchange interaction among all the La–Ba–Co–O compounds due to the straight Co–O–Co bond. The variation of the lattice parameter versus the calcium content exhibits a non-linear dependence and has the lowest value at x=0.05. In La0.6−xCaxBa0.4CoO3 compounds with x≤0.05, the magnetic frustration is observed below about 190K, and the substitution of Ca2+ for La3+ enhances the FM interaction due to the increasing double exchange through Co3+–O2−–Co4+ bond. The analysis based on the measured magnetization at 50kOe and the calculated value indicates that Co3+ ions are almost equally distributed at the low spin state and the intermediate spin state, and the Co4+ ions are at the low spin state. La0.55Ca0.05Ba0.4CoO3 has the lowest coercivity. As the composition deviates from x=0.05, the coercivity is enhanced. For the samples with θCW, the substitution of Ca2+ ions enhances the antiferromagnetic (AFM) interaction, and it is strong enough to make the long range AFM interaction appear. The percentage of the FM domains is calculated, and it decreases very quickly with the Ca2+ content x≥0.05. The sample with x=0.15 is mostly composed of AFM domains, and its AFM–FM transition temperature is 120K. Another FM interaction with a low magnetic moment at the low temperature is also observed.