Solvothermal Synthesis and Characterization of Fe3O4 and γ-Fe2O3 Nanoplates

γ-Fe2O3 nanoplates were prepared by a simple solution process and could be transformed to Fe3O4 nanoplates while keeping the size and morphology unchanged after reduction in hydrazine solution. The crystal structure and surface organic groups of the nanoplates were characterized in detail. The nanoplates exhibited good dispersibility in polar solvents except water and strong dipolar interactions, which favored the formation of one-dimensional chainlike structure. The poly(vinylpyrrolidone) molecules in this system played a key role for the growth of nanoplates, and it was supposed that the formation of nanoplates was a kinetically controlled process. The γ-Fe2O3 and Fe3O4 nanoplates with strong dipolar interactions are ferromagnetic at room temperature.