Intriguing structural and magnetic properties correlation study on Fe³⁺-substituted calcium-copper-titanate

This communication presents a detailed study on a Fe³⁺ modified CaCu₃Ti₄O₁₂ cubic perovskite system (CaCu_3-xTi_4-xFe_2xO₁₂ with x = 0.0-0.7) by performing X-ray powder diffractometry, DC SQUID magnetization and ⁵⁷Fe Mössbauer spectroscopy. The first ever Mössbauer studies on the system supported the reported peculiarity of the structure. Mössbauer analysis for the compositions x = 0.1, 0.3, and 0.5 suggest Fe³⁺ ions in two different environments. The site with larger quadrupole splitting corresponds to Fe³⁺ in the octahedral symmetry, while the site with lower chemical shift and quadrupole splitting belongs to Fe³⁺ in the square-planar (A'-) configuration. With the increase in Fe-substitution, Fe³⁺ appears to prefer A'- symmetry. Antiferromagnetic features are retained up to x = 0.3, but weak ferromagnetic characteristics appear with higher Fe³⁺ substitution. The switching of antiferromagnetic to ferromagnetic behavior was related to the preferential occupation of Fe³⁺ in square-planar symmetry accommodating Cu²⁺.