Structure and Mossbauer studies of Cu-doped Ni-Zn ferrite

Ni0.65Zn0.35 CuxFe2-xO4 (x = 0.0-0.3) was studied with X-ray diffraction, Mossbauer spectroscopy and vibrating sample magnetometer (VSM). The crystal structure was found to be a cubic spinel, and the lattice constants increased linearly with increasing quantity of Cu ions with the lattice constant a(0) = 8.384 +/- 0.005 Angstrom at x = 0.0. Mossbauer spectra of Ni0.65Zn0.35CuxFe2-xO4 (x = 0.0-0.3) were taken at various temperatures ranging from 12 to 725 K. As the temperature increased toward TN,a systematic line broadening effect in the Mossbauer spectra was observed and was interpreted as originating from different temperature dependencies of the magnetic hyperfine fields at various iron sites. The isomer shifts indicated that the iron ions were ferric at the tetrahedral CAI and the octahedral sites CBI. The quadrupole shifts showed that the orientation of the magnetic hyperfine field with respect to the principal axes of the electric field gradient was random. The magnetic hyperfine field values indicated that A sites had more A-O-B superexchange interactions than the B sites. The Neel temperature decreased with increasing quantity of Cu ions with T-N = 725 +/- 2 K at x = 0.0. Also, the Debye temperatures of the A and B sites of Ni0.65Zn0.35CU0.1Fe1.9O4 were found to be Theta(A) = 278 +/- 5 K and Theta(B) = 328 +/- 5 K. The VSM data showed that the magnetic moment decreased with increasing quantity of Cu ions with magnetic moment and coercivity values of M-s = 66 emu/g and H-c = 36 Oe at x = 0.3. (C) 2000 Elsevier Science B.V. All rights reserved.