Elucidating some issues regarding the synthesis of superparamagnetic-like single crystalline micrometric Fe3O4 during the hydrothermal process

Abstract

By hydrothermal decomposition of the Fe-EDTA complex, at 230°C, after 38 h of high -pressure treatment time, magnetite octahedrons with micrometric dimensions (15-45 µm) were obtained. Unusual and notable for these crystallites is the very small hysteresis surface, indicating a superparamagnetic-like behavior at micrometer scale, which means that the agglomeration of these crystallites is avoided after the removal of the magnetic field. This behavior can be correlated with a low level of imperfections in magnetite octahedrons, involving a low level of internal stresses, which leads to coercivity decreasing. The large dispersion in the crystallite axes is consistent with low remanence. We assumed that these attributes are related to the hydrothermal crystal growth process. To elucidate some issues regarding the magnetite crystallites development during the hydrothermal process, a careful observation of occurring intermediate phases by optical and SEM microscopy has been performed. Also the purity of the ferrous carbonate/magnetite mixture was analyzed by FTIR and Mössbauer spectroscopy