Emergent magnetic properties of biphase iron oxide nanorods

We report on the magnetic properties of biphase iron oxide nanorods (NRs) consisting of ferrimagnetic Fe3O4 and antiferromagnetic α-Fe2O3 phases. Annealing as-prepared NRs at 250 °C for 5h, significantly improved the crystallinity of the Fe3O4 phase and enhanced the volume fraction of the α-Fe2O3 phase. Magnetometry data consistently reveal these two magnetically distinct phases, which are not in proximity to each other but separated by a region of disordered spins giving rise to enhanced magnetization at low temperatures when the sample was cooled down from 300 K in the presence of a 1T field to 10 K. This phenomenon which is also known as the pinning effect is much more pronounced in the annealed sample, resulting from the increased volume fraction of the α-Fe2O3 phase which could strengthen the interfacial spin frustration between these two phases and enhance the density of disordered spins at the interface.