Thermomagnetic Stability of M-Type Strontium Ferrite (SrFe12O19) Particles with Different Shapes

M-type strontium ferrite (SrFe12O19: SrM) with two different shapes weresynthesized by a simple and benign process. One is peanut-like shape, and theother is hexagonal platelet. These shapes were controlled by the shape and size ofprecursor Fe3O4 particles. A mixture of submicron- or nanometer-sized Fe3O4particles and SrCO3 nanoparticles was calcined to transform to SrM, followed byacid-washing to remove secondary phase from SrM particles. Static magneticproperties, magnetic interactions, and thermomagnetic stability of the SrMparticles were studied. The measured saturation magnetization and intrinsiccoercivity are 74.2 emu/g and 4431 Oe, respectively, for the peanut-like SrMparticles and 73.6 emu/g and 5360 Oe for the hexagonal SrM platelets. Thesaturation magnetization is close to the theoretical value of 76 emu/g. Both typesof SrM show dipolar interactions and good thermomagnetic stability, i.e. α = Δσs/σs = −0.16%/K and β = ΔHci/Hci = 0.15%/K for the peanut-like SrM particles andα = −0.12%/K and β = 0.12%/K for the hexagonal SrM platelets. The temperaturecoefficient of intrinsic coercivity (β) is positive and magnetization still remainshigh at 400 K; 60 emu/g for the hexagonal SrM platelets and 50 emu/g for thepeanut-like SrM particles.