Manipulation Over Phase Transformation in Iron Oxide Nanoparticles via Calcination Temperature and Their Effect on Magnetic and Dielectric Properties

Iron oxide nanoparticles (IONPs) have gained technological importance in many fields that broadly includes health, environment, and energy applications. Consequently, the synthesis of IONPs with different phases and morphologies possesses significant interest. Therefore, here we report the facile synthesis of IONPs through the hydrothermal method followed by calcination process at different temperatures (300 °C, 500 °C, and 700 °C) and studied the influence of various phases of IONPs on their magnetic and dielectric properties. The structural studies using X-ray diffraction confirmed that the as-prepared material possesses the Fe
₃
O
₄
phase, and the increasing calcination temperatures leads to the phase transformation from maghemite (γ-Fe
₂
O
₃
) to hematite (α-Fe
₂
O
₃
) phase. The morphological studies revealed that the as-prepared material possesses flaky morphology with a size around 20 nm, γ-Fe
₂
O
₃
to have nanoparticles of sizes around 50 nm, and α-Fe
₂
O
₃
phase with mixed morphology of hexagonal and elongated shaped particles with size ranges from 60-140 nm. The optical properties of synthesized materials revealed that the band gap energy is found to be varied in between 2 and 2.7 eV depending upon the phase of IONPs. The hysteresis behavior of as-prepared and calcined IONPs at 300 °C and 500 °C indicated the soft-ferromagnetic properties of the phases. However, the IONPs prepared at 700° showed the weak-ferromagnetic property due to the existence of mixed α-Fe
₂
O
₃
phase. All the calcined IONPs showed the soft-ferromagnetic properties with saturation magnetization (M
_s
) that varied in between 47.88 and 0.35 emu/g. The occurrence of the reduced Ms ascribed to the phase transformation of the respective IONPs system. The dielectric studies of IONPs exhibited drastic variations with increasing frequency and with respect to their phase.