Temperature-Induced Irreversible Structural Transition in Fe(1.1)Mn(1.9)O(4) Nanoparticles Synthesized by Combustion Method

Fe(1.1)Mn(1.9)O(4) nanoparticles were successfully synthesized using a combustion method. The influence of the heating temperature on the evolution of the structural and magnetic properties has been studied using various methods. The structural analysis results revealed that as-synthesized nanoparticles have a tetragonal structure with an average size of ~24 nm. The magnetic measurements of the sample showed its ferrimagnetic nature at room temperature with hysteresis at low fields. Temperature-dependent magnetization measurements allowed for the conclusion that the Curie temperature for Fe(1.1)Mn(1.9)O(4) nanoparticles was ~465 °C. After high-temperature magnetic measurements, during which the samples were heated to various maximum heating temperatures (T(max.heat.)) in the range from 500 to 900 °C, it was found that the structure of the samples after cooling to room temperature depended on the heating temperature. Herewith, when the heating temperature was 600 < T(max.heat.) < 700 °C, an irreversible structural phase transition occurred, and the cooled samples retained a high-temperature cubic structure. The results of the magnetic analysis showed that the samples, following high-temperature magnetic measurements, demonstrated ferrimagnetic behavior.