Compositional behavior of heat capacity and magnetic properties in double spinel ferrites

Abstract

The purpose of the work is to identify the effects of the substitution of paramagnetic ions in ferromagnetic ferrites by diamagnetic components of zinc and aluminum. The following isomorphic spinel series are the object of review: Me(1-x)ZnxFe2O4 (Me – Ni, Co, Li, Cu, Mg) and Li0.5Fe2.5-xAlxO4 (x= 0-2.5). The single-phased samples were synthesized by ceramic procedure. Heat capacity near standard temperature Cp (298.15) was studied using calorimeter methods: drop calorimeter and DSC. Magnetic parameters – magnetic moments (M) and Curie temperatures (Tc) - were determined. All Me-Zn ferrite systems are characterized by dome-shaped correlations between heat capacity Cp(298) and composition (x), which have maximum values in the equimolecular region (x=0.4-0.6). This fact coincides with the nature of the compositional dependence of magnetic moments and indicates a significant effect of the excess magnetic contribution on the total heat capacity. A noticeable influence of the cooperative Jahn-Teller effect and the associated tetragonal distortion of the cubic lattice of Cu-Zn ferrites with a low Zn content (x<0.2) is observed, which causes overestimated values of the heat capacity of these compositions. Curie temperatures reveal the rectilinear decrease with increasing diamagnetic Zn and Al content in ferrite systems. The results are presented by graphs and tables.