Mn–Zn Ferrite Nanoparticles by Calcining Amorphous Products of Solution Combustion Synthesis: Preparation and Magnetic Behavior

Mn–Zn ferrite nanopowders were obtained by calcining diffraction-silent products of solution combustion at 650, 700, and 750°C and characterized by DTA/TGA, XRD, FTIR, SEM/EDX, ASA, and vibrational magnetometry. According to the data of synchronous thermal analysis, the formation of the manganese-zinc ferrite phase took place at 456°C. The results of powder X-ray diffractometry confirmed that, in all three cases, we observed the formation of Mn–Zn ferrite with an average crystallite size ( D ) ranging between 8.36 and 17.54 nm, the latter growing with increasing annealing temperature T . According to the data of adsorption-structural analysis, the largest specific surface area ( S = 71.96 m 2 /g) was observed at T = 650°C. After annealing at 750°C, S decreased down to 43.28 m 2 /g. Variation in T was found to affect the magnetic behavior of Mn–Zn ferrite nanoparticles. The appearance of M–H hysteresis loops is indicative of superparamagnetic behavior of synthesized nanoparticles which is supported by low values of coercive force ( H c = 23.7 Oe), remanent magnetization ( M r = 1.47 emu/g), and saturation magnetization ( M s = 13.67 emu/g). Upon an increase in T , the magnetic behavior of synthesized Mn–Zn ferrites got closer to that of soft ferrites. The maximum values of H c , M s , and M r observed at T = 750°C had a value of 53.2 Oe, and 52.55 and 16.23 emu/g, respectively.