Effect of substitutions on the phase formation, structure and magnetic properties of the double perovskites Sr2MnSbO6 and SrLaMnSbO6

•Two solid solutions: Sr2-xLaxMnSbO6 (x = 0.25, 0.50. 0.67 and 0.75) and Sr1.5La0.5Mn1+xSb1-xO6 (x = 0.25 and 0.50) were prepared through solid state synthesis at ordinary condition.•The chemical composition, crystal structure and magnetic properties of SS were studied based on mixed Mn2+/Mn3+ and Mn3+/Mn4+ oxidation states, respectively.•The structure of first group samples was characterized by the monoclinic space group P21/n containing alternating MnO6 and SbO6 octahedra with unit cell volume increasing with × and prevailing antiferromagnetic exchange interaction at low temperatures.•The result of change of a ratio of Mn/Sb in Sr1.5La0.5Mn1+xSb1-xO6 in favor of Mn (x = 0.25 and 0.5) is phase separation of system on the orthorhombic Pnma and ferromagnetic rhombohedral Rc phases. Solid solutions (SS) based on Sr2MnSbO6 and SrLaMnSbO6 with mixed oxidation states of Mn have been prepared by solid state synthesis under standard conditions. The structural and magnetic properties of Sr2-xLaxMnSbO6 and Sr1.5La0.5Mn1+ySb1-yO6 have been studied using X-ray diffraction data and magnetic susceptibility χ and magnetization σ measurements at 2–400 K. The samples of the first group crystallize in the monoclinic space group P21/n, their unit cell volume increases with × due to the formation of mixed Mn3+/Mn2+ valence. The change of the Weiss constant Θ sign from positive to negative with variation of ×, as well as the divergence between FC and ZFC dependences χ(T) below 40 K and spin-glass behavior indicate that the dominant exchange interactions between Mn3+ and Mn2+ cations in Sr2-xLaxMnSbO6 are of antiferromagnetic nature. The samples of the second group (at y = 0.25 and 0.50) were characterized as non-uniform, containing apparently two phases with a mixed Mn3+/Mn4+ state. The composition of the phases was established approximately by studying their structural and magnetic characteristics. The composition and crystal structure of the main phases are similar to those of the monoclinic samples described above. The secondary phases are identified as rhombohedral (space group R3¯c) with ferromagnetic properties with TC of 304.2 K (y = 0.25) and 365 K (y = 0.50).