Study of the lattice structure and magnetic spin order modification in chemical routed α-Fe1.4Cr0.6O3 oxide as an effect of heat treatment

The Cr doped hematite (α-Fe_1.4Cr_0.6O₃) system has been prepared by chemical route. The chemical routed sample has been thermally annealed at different temperatures in the range 800-1000 °C to study modified lattice structure and magnetic spin order. The present Cr doped hematite samples do not exhibit Morin transition, a typical temperature that marks spin orientation from in-plane spin to out of plane directions in hematite system. A distinct change in magnetic properties has been seen by increasing the annealing temperature. The sample prepared by annealing at 800 °C showed superparamagnetic blocking of particles below 38 K. Ac susceptibility data have been used to study the mechanism of spin dynamics around the blocking temperature. Such blocking behaviour of particles is not observed in the samples annealed at 900-1000 °C. The modified spin order in the samples has been understood by using core-shell model of antiferromagnetic particles. Mössbauer spectra of the samples have confirmed a transformation of the spin order with the increase of annealing temperature and support the features observed from dc magnetic measurements.