Molecular field coefficients and cation distribution of substituted yttrium iron garnets

The saturation magnetization M_s(T) of Ga, Al, Sc, and CaVBi substituted Y₃Fe₅O₁₂ (YIG) single crystals and of polycrystalline Ca/Ge and Ca/Ti substituted YIG has been investigated for 4.2 K ⩽T⩽T_C. The samples were repeatedly annealed and quenched at different equilibrium temperatures 773 K⩽T_e ⩽1523 K. The attained site exchange of Fe and the substituents between the a and d sites resulted in considerable changes of M_s(T). From a fit of the Néel molecular field theory to the M_s(T) data the dependence of the magnetic moments at T = 0 K and of the molecular field coefficients on the amount of nonmagnetic substitutions on the a and d sites were determined. It turned out that ion‐specific sets of equations are required accounting for the ’’particular ion effect’’ of different cation species. The cation distributions inferred from the magnetic data have been analyzed along with a thermodynamic equilibrium model. The derived site stabilizing energies for the mixed Fe–Ga and Fe–Al garnets agree well with recently reported data. New results are presented for the site stabilizing energies in Ca/Ge:YIG and for the substituents Sc and Ti with octahedral site preference.