Evolution of Structure, Magnetism, and Critical Behavior of Nanocrystalline BaCo1-yMnyO3-δ (0.0 ≤ Y ≤ 0.3).

We report the structural, magnetic, and magnetocaloric properties of the nanocrystalline BaCo1-yMnyO3-δ (0 ≤ y ≤ 0.3) samples synthesized by sol-gel method. The samples crystallized into different hexagonal polytypes as a function of composition and annealing temperature. The crystal structure of parent BaCoO3 (y = 0) changed from 2H- to mixed 2H+10H (y = 0.3) through 2H+12H (y = 0.2) hexagonal phase for 900 °C annealed samples. The increase in annealing temperature reduces the fraction of face sharing octahedra, and the crystal structure of 1100 °C samples exhibited 2H+12H, 12H, 12H+10H, and 2H+10H- hexagonal phases. The relationship between structural and magnetic properties is explained by the structural spin model projection. The 2H- and 10H-hexagonal phases exhibited antiferromagnetic ordering, whereas 12H- phase attributed to ferrimagnetic ordering. The critical exponent analysis indicates that the 12H- hexagonal phase exhibits mean-field approach and the other mixed hexagonal polytypes do not follow any universal model. [ABSTRACT FROM AUTHOR]