Cation Distribution and Temperature Dependence of Brillouin Function for Nickel-Substituted Manganese–Zinc Ferrites

Ni-substituted manganese-zinc (MnZn) ferrites with the composition of Mn
_0.506-x
Zn
_0.244
Ni
_x
Fe
_2.250
O
_4.0
(x = 0.066~0.122) have been prepared by the solid-state reaction method. The cation distribution has been investigated by the Rietveld refinement of X-ray diffraction patterns, the microstructure has been observed using a scanning electron microscope, and the magnetic property has been measured using superconductor quantum interference devices and B-H analyzer. The results show that Zn
²⁺
and Ni
²⁺
ions prefer to occupy the tetrahedron site (A sublattice) and octahedron site (B sublattice), respectively. However, Mn
²⁺
and Fe
³⁺
ions can enter into A and B sublattices, where the ratio of Mn
²⁺
ions occupying A and B sublattices is 4:1. The lattice parameter (a) of the samples decreases with the increase of Ni-substituted content. Meanwhile, based on the Neel model of collinear-spin ferrimagnetism, the molecular-field coefficients ω
_AA
, ω
_BB
, and ω
_AB
of the Ni-substituted MnZn ferrites have been calculated, and the magnetic moment of A and B sublattices versus temperature T has also been investigated. The fitting results match well with the experimental data. Both ω
_AB
and ω
_BB
increase with the increase of the Ni-substituted content, but ω
_AA
shows the opposite variation trend. The Curie temperature also increases with the increasing of the Ni-substituted content, which is attributed to the enhancement of superexchange interaction for A-B sublattice. In addition, the temperature dependence of initial permeability and core loss has been discussed.