Ellipsometric investigation of ZnFe_2O_4 thin films in relation to magnetic properties

摘要

We report an influence of disorder on structural and magnetic properties of ZnFe_2O_4 thin films grown at temperatures ranging from 400 ℃ to 600 ℃ by pulsed laser deposition in O_2 atmosphere on SrTiO_3 (100) substrates evidenced by properties of electronic transitions observed in the dielectric function. Inversion of the normal spinel structure was found to be one of the main mechanisms responsible for the increase in the magnetic response for the lowest growth temperature. The enhanced feature in the dielectric function located at ～3.5 eV, related to the transition involving tetrahedrally coordinated Fe~(3+) cations, corresponds to the dominating magnetic coupling between the octahedral and tetrahedral lattice sites, responsible for the overall ferrimagnetic behaviour of the film grown at the lowest temperature.