Thermomagnetic stability of M-type strontium ferrite (SrFe 12 O 19 ) particles with different shapes

M-type strontium ferrite (SrFe 12 O 19 : SrM) with two different shapes were synthesized by a simple and benign process. One is peanut-like shape, and the other is hexagonal platelet. These shapes were controlled by the shape and size of precursor Fe 3 O 4 particles. A mixture of submicron- or nanometer-sized Fe 3 O 4 particles and SrCO 3 nanoparticles was calcined to transform to SrM, followed by acid-washing to remove secondary phase from SrM particles. Static magnetic properties, magnetic interactions, and thermomagnetic stability of the SrM particles were studied. The measured saturation magnetization and intrinsic coercivity are 74.2 emu/g and 4431 Oe, respectively, for the peanut-like SrM particles and 73.6 emu/g and 5360 Oe for the hexagonal SrM platelets. The saturation magnetization is close to the theoretical value of 76 emu/g. Both types of SrM show dipolar interactions and good thermomagnetic stability, i.e. α = Δ σ s / σ s = −0.16%/K and β = Δ H ci / H ci = 0.15%/K for the peanut-like SrM particles and α = −0.12%/K and β = 0.12%/K for the hexagonal SrM platelets. The temperature coefficient of intrinsic coercivity ( β ) is positive and magnetization still remains high at 400 K; 60 emu/g for the hexagonal SrM platelets and 50 emu/g for the peanut-like SrM particles.