High temperature spin state transitions in misfit-layered Ca3Co4O9

• Ca3Co4O9 system has been fabricated using the solid-state technique.
• There is an anomaly in magnetic the susceptibility χ between 680 and 920 K.
• The anomaly is related to a critical threshold number of the high spin Co-ions.
• The anomaly was also observed in the B and Sb-substituted Ca3Co4O9.

This study reports high temperature magnetic properties of the unsubstituted one together with B and Sb-substituted Ca3Co4O9 system. The measured data indicated that there is an anomaly in the magnetic susceptibility, χ, between 680 and 920 K. It is believed that this anomaly is related to a critical threshold number of the high spin Co-ions such that when this threshold number is achieved, some exchange interactions between Co3+ and Co4+ take place which causes an abrupt increase in the χ–T curve. The anomaly was further investigated with B and Sb-substitutions. It is realized that both dopants promote more Co-ions in the rock salt unit cell to high spin state.