Temperature selectivity for single phase hydrothermal synthesis of PEG-400 coated magnetite nanoparticles

Herein, we have presented a detailed investigation of the temperature effect on hydrothermal synthesis of Fe(3)O(4)magnetic nanoparticles (MNPs). The appearance of single-phase cubic spinel Fe(3)O(4)at and above critical temperature provides a clear indication that temperature plays a crucial role in the single-phase synthesis of the Fe(3)O(4)MNPs. A detailed investigation of the structural, magnetic and spin dynamic properties of PEG-400 coated Fe(3)O(4)MNPs synthesized by a facile hydrothermal method at different temperatures (120 degrees C, 140 degrees C, 160 degrees C and 180 degrees C for 16 hours) has been presented. The single-phase cubic magnetite structure with high crystallinity was found in the samples synthesized at 160 and 180 degrees C and confirmed from XRD results, whereas samples prepared at 120 and 140 degrees C are of mixed phase (alpha-Fe(2)O(3)and Fe3O4). The magnetic hysteresis curves reveal that saturation magnetization and coercivity of MNPs enhanced systematically with the increase in the reaction temperature from 120 degrees C to 180 degrees C. Maximum saturation magnetization (88.98 emu g(-1)) and coercivity (134.16 Oe) were found for the sample synthesized at 180 degrees C. Furthermore, ferromagnetic resonance (FMR) spectra obtained for samples synthesised at higher temperatures indicate a lower value of the line width due to the high magnetic ordering in the samples. Also, the resonance field decreased, and theg-value increased due to enhancement in magnetization for the single-phase samples synthesized at higher reaction temperatures. The spin resonance properties obtained from fitting the FMR data clearly indicate that a large spin-orbit coupling was observed for the single phase Fe(3)O(4)MNPs and excellent magnetic properties were obtained from the static magnetic measurements.