Cation distribution effect on electronic, magnetic structure and optic properties in cobalt ferrites (Co1−yFey)Tet(CoyFe2−y)OctO4 with disordered spinel structure

Abstract

Cation disorder in cobalt ferrite spinels have significant effects on its electronic, magnetic and optic behavior. The cations inversion effect between tetrahedral (Td) and the octahedral (Oh) positions on electronic and magnetism in Co1−yFey(CoyFe2−y)O4 with 0 ≤ y ≤ 1 cobalt ferrites is reported. It is found that cobalt ferrites exhibit strong ferrimagnetic ordering between both sites (Oh) and (Td). In addition, It is concluded that the arrangement of the Co(Oh)-Fe(Td) pair is preferred and total energy depend strongly on the occupation of Co and Fe on (Td) and (Oh) positions respectively. A moderate tendency for cation inversion in the compound under study is obtained within GGA + U. The results also show while the magnetic moment of Cotet/Feocta or Coocta/Fetetra almost is constant, the total spin magnetic moment decreases linearly with y from 7.00 μB for y = 0 up to 3.00 μB for y = 1. It is noted that the cell parameters appear to be sensitive to the degree of order. The optimized structures show that with inversion parameter y, the lattice parameter increases by 3.5%. The obtained electronic structure (GGA + U) shows that the compounds are magnetic semiconductors or half metals (y = 0.25) and a gapless semiconductor for (y = 0.5, 0.625 and y = 0.75) according to the degree of inversion of predominantly ionic nature. Meanwhile, the spin bandgap for the majority spin channel varies with increasing y from 2.42 eV for y = 0 to 1.83 eV for y = 1. Moreover, dielectric function, reflectivity and absorption coefficients as functions of wavelength of incident light are calculated and interpreted. Interestingly, reflectivity and absorption coefficients are found to exhibit strong variation with the inversion parameter.