Mössbauer Studies of NiZnCu Ferrite

Ni_0.65Zn_0.35Cu_xFe_2-xO₄ (x = 0.0 - 0.3) was studied with X-ray diffraction, Mössbauer spectroscopy and VSM. The crystal structure is found to be a cubic spinel, and the lattice constants increased linearly with increasing quantity of Cu ions with the lattice constant a₀ = 8.384 Å at x = 0.0. Mössbauer spectra of Ni_0.65Zn_0.35Cu_xFe_2-xO₄ (z = 0.0 - 0.3) were taken at various temperatures ranging from 12 K to 725 K. As the temperature increased toward T_N, a systematic line broadening effect in the Mössbauer spectra was observed and was interpreted as originating from the 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 [A] and the octahedral sites [B]. The quadrupole shifts showed that the orientation of the magnetic hyperfine field with respect to be 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 did. The Néel temperature decreased with increasing quantity of Cu ions with T_N = 725 K at x = 0.0. Also, the Debye temperatures of the A sites and the B sites of Ni_0.65Zn_0.35Cu_0.1Fe_1.9O₄ were found to be Θ_A = 228±5 K, and Θ_B = 377±5 K and decreased with increasing quantity of Cu ions. The VSM data showed that the magnetic moment decreased with increasing quantity of Cu ions with magnetic moment and coercivity values of M_s=75 emu/g and H_c=47 Oe at x = 0.1.