The formation and properties of a system of iron oxide nanoclusters

Nanoclusters of iron oxides with sizes varying from 1 to 30 nm are synthesi zed and their properties are studied. System of clusters is prepared by a t opochemical reaction of thermal decomposition of iron oxalate. Cluster size s were measured by varying the decomposition temperature T-d and controlled by gamma-resonance (Mossbauer) spectroscopy and atomic force microscopy. D ata on DGA and DTA, as well as the treatment of the thermodynamic model of cluster nucleation, indicate that the system of iron oxide clusters may be either weakly interacting system 1 or strongly interacting system 2. System 1 is formed from noncontacting clusters with dimensions 1-10 nm at T-d = 2 00-260 degrees C; system 2 is formed from sintering clusters with the sizes 10-30 nm at T-d = 260-300 degrees C System 1 is characterized by superpara magnetic and superferrimagnetic properties. In system 2, superparamagnetism is absent, albeit a first-order magnetic phase transition appears at clust er sizes smaller than R-cr; at this transition, magnetic ordering and magne tization of a system change in a jump-wise manner. It was noticed also that the temperature of the magnetic phase transition lowers significantly as c ompared with bulk the sample of iron oxide.