Crystal structure and magnetic properties of high-coercivity Sr1 − x Pr x Fe12 − x Zn x O19 solid solutions

Abstract

Sr1−x Pr x Fe12 − x Zn x O19 ferrites with x = 0, 0.1, 0.2, 0.3, 0.4, and 0.5 have been prepared by solid-state reactions between praseodymium, iron, and zinc oxides and strontium carbonate in air at 1470 K. According to X-ray diffraction results, the samples with x ≤ 0.2 were single-phase and those with 0.3 ≤ x ≤ 0.5 contained, in addition to the magnetoplumbite phase, small amounts of α-Fe2O3, ZnFe2O4, and PrFeO3. The mixed-phase samples further fired twice at 1470 K for 4 and 2 h contained no impurity phases at x = 0.3 and contained only α-Fe2O3 at x = 0.4 and 0.5. In the composition range 0 ≤ x ≤ 0.3, the a and c cell parameters, unit-cell volume V, and X-ray density ρx of the magnetoplumbite phase vary linearly according to the relations a(A) = 5.8869 − 0.0162x, c(A) = 23.027 + 0.449 x, V(A3)= 691.10 + 9.65x, and ρx(g/cm3) = 5.102 + 0.230 x. The highest degree of combined heterovalent substitution of Pr3+ for Sr2+ and Zn2+ for Fe3+ in the SrFe12O19 ferrite (formation of Sr1−x Pr x Fe12 − x Zn x O19 solid solutions) at 1470 K is x = 0.32−0.36. The saturation magnetization per formula unit (n s) of the x = 0.1 ferrite exceeds that of SrFe12O19 by 1.7% at 6 K and by 15.2% at 308 K. The 308-K n s and coercive force (σ H c) of the x = 0.2 ferrite exceed those of SrFe12O19 by 7.6 and 8.5%, respectively.