Structure and magnetic properties of Zr–Mn substituted strontium hexaferrite Sr(Zr,Mn) x Fe12−2x O19 nanoparticles synthesized by sol–gel auto-combustion method

In this research, nano-sized powders of Zr–Mn substituted strontium hexaferrite (Sr(Zr,Mn) x Fe12−2x O19 (x = 0, 2, 2.5, 3)) were synthesized by sol–gel auto-combustion route using subsequent heat treatment. The samples were characterized using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), field emission scanning electron microscope (FESEM), transmission electron microscopy (TEM), Mossbauer spectroscopy and vibration sample magnetometer (VSM) techniques. XRD and Mossbauer spectroscopy results revealed formation of Sr(Zr,Mn) x Fe12−2x O19 accompanied with Mn δ Fe2−δ O4 lateral phase in the samples. Also, FTIR and XRD results demonstrated presence of SrO impurity phase. FESEM micrographs show particle size reduction and presence of two distinct powder morphologies with different brightness levels with Zr4+ and Mn2+ substitutions which approves existence of lateral phases in the substituted samples. TEM micrographs show nanometric particles with sizes smaller than 100 nm with high crystallinity. Mossbauer results showed that at low level of substitution, Zr4+ ions prefer to occupy both 4f1 and 2b however, at higher level of substitution, they prefer exclusively 4f1 site. While, Mn2+ ions distributed approximately equally between 12k and 2a sites. The presence of nonmagnetic Zr4+ cation leads to decrease in exchange interaction, especially at 12k and 2a sites. VSM results showed decrement of coercivity force ( i H c ) from 5593.60 to 3282.46 Oe and maximum magnetization from 62.60 to 46.15 emu g−1, respectively, by increment of Zr–Mn substitution values. Variations in maximum magnetization magnitude have been explained on the basis of occupation of the substituted cations at different iron sites.