Crystal structure and magnetic properties of Sr1 ? x Sm x Fe12 ? x Co x O19 solid solutions

Sr_{1 ? x} Sm _x Fe_{12 ? x} Co _x O₁₉ (0 ≤ x ≤ 0.5) ferrites have been prepared by solid-state reactions in air at 1470 K using mixtures of samarium oxide, ferric oxide, Co₃O₄, and strontium carbonate. X-ray diffraction characterization showed that the samples with x < 0.2 were single-phase, whereas the samples with 0.2 ≤ x ≤ 0.5 contained α-Fe₂O₃ and those with 0.3 ≤ x ≤ 0.5 contained SmFeO₃, CoFe₂O₄, and Sm₂O₃ as well. The highest degree of Sm³⁺ and Co²⁺ substitutions for Sr²⁺ and Fe³⁺ (x) in the SrFe₁₂O₁₉ ferrite at 1470 K was determined to be slightly less than 0.2. This substitution only slightly decreases the a and c parameters of the hexagonal lattice and the Curie temperature (T _C) of the material. At temperatures of 5 and 300 K in magnetic fields of up to 14 T, we obtained magnetic hysteresis loops, which were used to evaluate the spontaneous magnetization (σ₀), specific saturation magnetization (σ_s), and coercive force (_σ H _c) of the ferrites. The experimentally determined 5-K spontaneous magnetization per formula unit (n ₀) of the x = 0.1 ferrite is 20.86μ_B, which coincides with the theoretical value calculated as n ₀ = (8 × 5) ? (3.9 × 5 ? 0.1 × 3) = 20.8μ_B. At 300 K, the n ₀ and _σ H _c of Sr_0.9Sm_0.1Fe_11.9Co_0.1O₁₉ exceed those of SrFe₁₂O₁₉ by 7.7 and 9.9%, respectively.