Dilute ferrimagnetism of ilmenites Mn$_{3}$FeTiSbO$_{9}$ and Mn$_{4}$FeTi$_{2}$SbO$_{12}$

Metastable solid solutions (SS) Mn$_{3}$FeTiSbO$_{9}$ and Mn$_{4}$FeTi$_{2}$SbO$_{12}$ with the ilmenite structure (space group $R\bar3$) have been prepared by quenching at normal conditions. The compositions of the compounds have been justified using EDX spectroscopy and X-ray diffraction. The magnetic properties of SSs have been analyzed by comparison with ferrimagnetic ilmenite Mn$_{2}$FeSbO$_{6}$ ($T_{N}$ = 269 K) as a natural mineral and ceramics obtained at high pressure and high temperature. The solid solutions have been characterized as dilute magnetic systems formed as a result of substitution of nonmagnetic cations Ti$^{4+}$ for a part of Fe$^{3+}$ and Sb$^{5+}$ cations. Mn$_{3}$FeTiSbO$_{9}$ is considered as a ferromagnetic with $T_N$ = 171 K and Mn$_{4}$FeTi$_{2}$SbO$_{12}$ as a magnetic with the concentration of magnetic clusters below the percolation threshold.