Mechanism of high temperature induced phase transformation and magnetic properties of Mn3O4 crystallites

Abstract This paper is an experimental study of the different phases of oxides of manganese, prepared by solution combustion method using mixture of urea and glucose as fuels. To validate the thermal stability of Mn 2 O 3 , the as-synthesized sample was subjected to heat treatment from 350 °C to 1000 °C with 100 °C interval. The change in Mn 2 O 3 to Mn 3 O 4 was identified by powder X-ray diffraction (PXRD) to show the temperature dependent phase transformation that occur during the heat treatment process. The PXRD patterns show that Mn 2 O 3 is stable between temperatures of 350 °C to 850 °C, and a new phase i.e Mn 3 O 4 appears at 1000 °C. The Mn 2 O 3 and Mn 3 O 4 have their distinct surface morphologies viz., spherical and rod shapes. The detailed morphology, elemental compositions and structure investigation were carried out by using Scanning Electron Microscopy (SEM-EDAX) and Raman spectroscopy. Sintered sample of Mn 3 O 4 were subjected to magnetic measurements. The Mn 3 O 4 crystallite with diameters of 50 nm shows ferromagnetic behavior with a phase transition from ferromagnetic to paramagnetic phase at 48 K. A large coercivity up to 3000 Oe and a small remanence of 0.1092 emu/g at 10 K, was observed. The temperature dependent magnetization measured in a magnetic field of 100 Oe, increases significantly with decreasing temperature around 45 K, both for the FC and ZFC measurements. The susceptibility measurement of the Mn 3 O 4 crystallites were investigated between 0 and 300 K by applied magnetic fields up to 5 T. A magnetic transition is observed near 48 K which is attributed to the formation of the ferrimagnetic Mn 3 O 4 .