Formation of various iron oxides and oxy-hydroxides was monitored during the hydrolysis of ferric nitrate with hydrazine monohydrate under sonication. The hydrolysis of a concentrated solution (0.05 M) of ferric nitrate solution resulted in the formation of gamma-Fe2O3 as the major product and that of a lower concentration (0.005 M) formed alpha-FeOOH as the major product and at intermediate concentrations, gamma-FeOOH or a mixture of gamma-FeOOH and alpha-FeOOH was formed. The shape of the particles varied. from spherical to acicular to rod shaped as a result of the changes in the phases formed. The as-formed gamma-Fe2O3 exhibited a saturation magnetization of 65 emu/g where as the as-prepared alpha-FeOOH exhibited a very weak magnetic moment of around 4 emu/g. (C) 2015 Elsevier B.V. All rights reserved.