Effect of the synthesis method on the heating ability and physicochemical properties of gallium and strontium-substituted manganese ferrites

Abstract

The feasibility of synthesizing Mn_1-xSr_xFe₂O₄ and Mn_0.95-xGa_0.05Sr_xFe₂O₄ (x = 0, 0.05, 0.10, 0.15, 0.20) by both coprecipitation and sol-gel routes, has been demonstrated. In all the cases, a single crystalline phase, was detected. This phase corresponds to an inverse spinel structure. Crystallite size was larger for the samples obtained by sol-gel (15–19 nm) than that of the samples obtained by coprecipitation (10–13 nm). The hysteresis loops indicated that ferrites showed a behavior close to that of the superparamagnetic materials. Higher saturation magnetization (M_s) values were observed for the coprecipitation synthesized samples, exhibiting values of up to 67 emu/g for Mn_0.90Ga_0.05Sr_0.05Fe₂O₄. On the other hand, the lower remanent magnetization (M_r) and coercive field (H_c) values were observed for the samples obtained by sol-gel. The heating ability of the sol-gel synthesized ferrites was considerably higher than that observed for the samples obtained by coprecipitation, reaching temperatures of up to 73 °C for the aqueous suspension containing 10 mg of Mn_0.80Ga_0.05Sr_0.15Fe₂O₄/mL. The Fourier transform infrared spectroscopy (FTIR) results showed the presence of absorption bands corresponding to C–O, C–H–C and CC, which may indicate that the ferrites obtained by sol-gel are either partial coated or functionalized. The incorporation of Ga and Sr into the crystalline structure of the manganese ferrite was demonstrated. Finally, polycrystalline spheric nanoparticles, with an average size of 18 nm, were obtained for the sol-gel synthesized Mn_0.80Ga_0.05Sr_0.15Fe₂O₄. The nanoparticles obtained by both methods show the heating ability required for magnetic hyperthermia treatment.