Magnetic properties of Mn0.1Mg0.2 TM 0.7Fe2O4 (TM =Zn, Co, or Ni) prepared by hydrothermal processes: The effects of crystal size and chemical composition

Highlights: • Mn_0.1Mg_0.2(Co, Ni, Zn)_0.7Fe₂O₄ nanoferrites were synthesized by hydrothermal process. • Chemical composition and crystallite size have significant effects on the magnetic properties. • Enhanced magnetization (∼90 emu/g) in the Co-based oxide makes it a best candidate for application requiring high magnetization. Nano-crystalline Zn-, Co-, and Ni-substituted Mn-Mg ferrites were prepared by hydrothermal process and annealed at 1100 °C. Annealing conditions are critical on the crystalline phase. TEM and XRD data reveal particle sizes between 8 nm and 15 nm for the as-prepared fine powders, which increase to about 73 nm after sintering at 1100 °C. Mssbauer spectra show well resolved magnetic splitting in bulk samples. The as-prepared fine powders show weak hyperfine splitting and broad central doublets associated with fine particles. Magnetization data reveal a high coercive field at about 300 K of about 945 Oe in the Co-based nanosized oxide, which reduces to about 360 Oe after thermal annealing at 1100 °C. The magnetization curves of Zn- and Ni-based samples show much lower coercive fields indicative of superparamagnetic nanoparticles. The crystallite size and chemical composition have significant effects on the properties of ${\text{Mn}}_{0.1}{\text{Mg}}_{0.2}{\text{(Zn,Co,Ni)}}_{0.7}{\text{Fe}}_2{\text{O}}_4$ investigated.