Magnetic and Crystalline Behavior of Certain Oxide Systems with Spinel and Perovskite Structures

A series of substitutions have been performed on nickel ferrite where the Fe³⁺ is replaced, by varying amounts, with In³⁺, Sc³⁺, Y³⁺, Gd³⁺, and La³⁺. In³⁺ went into solid solution with the nickel ferrite to form a spinel structure whose lattice constant a₀ increased linearly with increasing amounts of In³⁺ to a maximum value of 8.708A for 1.5 In³⁺ ions per molecule. At greater concentration of In³⁺, the starting materials appeared as a mixed phase with NiO·{}Fe0.5{In}1.5O₃. The saturation magnetization (μ₀), obtained by extrapolation to absolute zero, increased with increasing amounts of In³⁺, in a manner indicating that the In³⁺ ions preferred the A sites. In the case of Sc³⁺, an increased cell size was found which "leveled off" at a₀=8.41A for 0.75 Sc³⁺ ions per molecule. μ₀ decreased with increasing Sc³⁺ content and approached a compensation point similar to that found previously for the Al³⁺ substitution. It is concluded that trivalent metal ions having a rare gas electronic structure, by showing a preference for the B sites, give rise to compensation points and the N\'eel P-type curves. The Curie temperatures for the substitution of In³⁺ and Sc³⁺ show a nearly linear decrease with con-concentration but with slopes greater and less, respectively, than the slope of the single curve found previously to represent both the Al³⁺ and Ga³⁺ substitutions. The Y³⁺, Gd³⁺, and La³⁺ substitutions resulted in a mixed solution of nickel ferrite and corresponding perovskite structures formed with Fe³⁺.