Understanding the structural behaviors and abrupt enhancement in magnetic ordering temperature of Fe-substituted Mn3O4

We report an increase in magnetic ordering temperature from 43 K to 425 K and a structural phase transition from tetragonal I41/amd (x = 0.00) to cubic Fd3m (x = 0.40) in (Mn1-xFex)(3)O-4 (x = 0.00-0.40) systems. The phase diagram clearly demonstrates that lattice constants a root 2 and c converge smoothly with Fe-substitution and become equal for x = 0.40, while the room temperature magnetic moments increase from 0.15 mu B/f.u. (x = 0.10) to 1.1 mu B/f.u. (x = 0.40). There are two possible cationic distribution scenarios for Fe cations; one leads Fe2+ to occupy the tetrahedral site, while the other leads Fe3+ to occupy the octahedral site. The octahedral site preference energy indicates that Fe3+ cations occupying the octahedral site have higher preference values. X-ray absorption spectra studies of MnL2,3-edge and FeL2,3-edge confirm that Fe3+ cations occupy octahedral sites by replacing Jahn-Teller active Mn3+ cations. OK-edge spectra revealed that Jahn-Teller distortion is reduced in the cubic x = 0.40 system. However, the higher structural symmetry is not the most significant factor in the abrupt enhancement of magnetic ordering temperature. The increase in magnetic ordering temperature could be un-derstood on the basis of increased spin moment coupling between tetrahedral and octahedral cations due to substitution of Fe3 thorn cations at the octahedral site.