Sintering temperature effects on bond geometry, particle fraction, band gap, Poisson's ratio, heat capacity, superparamagnetism, and polarization of manganese nanoferrite

Mn-ferrites have attracted significant attention for biomedical applications due to their versatile functional properties, particularly superparamagnetism, which can be optimized through controlled sintering. This study investigates the effects of four sintering temperatures (600 °C, 650 °C, 700 °C, and 750 °C) on the multifunction characterization of normal Mn-ferrite (u = 0.375 Å) synthesized via the chemical co-precipitation technique with double sintering effect and pH adjustment. XRD analysis confirms a cubic spinel structure (Fd 3 m- O h 7 space group), with crystallite sizes of 16.62–18.93 nm and interionic bond angles θ 2 A − O − B , θ 4 B − O − B and θ 5 A − O − A around 154°45′, 125°15′, and 79°58′, respectively. TEM shows nanoparticles averaging 16.77–19.02 nm, with microvoid fraction decreasing from 69.29 % to 18.78 %, and particle fraction increasing from 30.71 % to 81.22 % with temperature. UV–Vis analysis reveals a tunable band gap (1.30–2.23 eV) and Urbach energy (0.5345–0.395 eV). FT-IR spectra confirm Mn–O and Fe–O bond vibrations at 981.77 and 848.68 cm −1 , with decreasing exothermic lattice energy (95.95–92.34 eV/ion). Elastic analysis shows a stable Poisson's ratio (0.47) and Einstein temperature (654.84–655.50 K). Thermodynamically, Mn-ferrite maintains consistent heat capacity with a slight Debye temperature drop (449.77–439.46 K). Magnetically, higher sintering reduced remanent magnetization (0.9541–0.3472 emu/g) and coercivity (204.05–24.73 Oe), indicating enhanced superparamagnetism supported by lower relaxation time (1.60944–0.72622 ns) and blocking temperature (5.56–0.56 K). Based on Maxwell-Wagner-type polarization, both the real dielectric constant and losses decrease as alternating fields increase, stabilizing at higher frequencies. Notably, this study shows that higher sintering temperatures significantly reduce microvoids and enhance nanoparticle formation, thereby optimizing the superparamagnetic and dielectric behavior, indicating the suitability of Mn-nanoferrite for biomedical applications.