Atomic migration and superexchange interaction in Ni0.1Cu0.9Fe2O4

Ni-0.1 Cu0.9Fe2O4 was studied with X-ray diffraction and Mossbauer spectros copy, The crystal structure was found to be a cubic spinel with the lattice constant a(o) = 8.386 +/- 0.005 Angstrom. The Neel temperature was determi ned to be T-N = 755K for a heating rate of 5K/min, The Mossbauer spectra co nsisted of two six-line patterns corresponding to Fe3+ at the tetrahedral(A ) and octahedral (B) sites. Debye temperatures for A and B sites were found to be 568 +/- 5K and 194 +/- 5K, respectively. Atomic migration of Ni-0.1 Cu-0.9 Fez O-4 starts near 350K and increases rapidly with increasing tempe rature to such a degree that 71% of the ferric ions from the A sites moved to the B sites at 550K, The temperature dependence of the magnetic hyperfin e field of Ni-0.1 Cu-0.9 Fe2O4 was explained by the Neel theory of ferrimag netism using three superexchange integrals: J(A-B) = -29.2k(B), J(A-A) = -2 1.9k(B), J(B-B) = 0.5k(B).