Annealing effects on the structural, magnetic and electrical properties of the nanocrystalline Fe3O4 films

Nowadays, the effective spin injection across the surface or interface between the magnetic injector and the insulating barrier is one of the key issues and big challenges in realizing potential spintronic devices. In this paper, we report the annealing effects on the structural, magnetic and electrical properties of nanocrystalline Fe3O4 films. The width and height of the tunnelling barrier in these nanocrystalline films can be adjusted by vacuum and/or air annealing. The structural, chemical states, magnetic and electrical measurements indicate a good stoichiometry of Fe3O4 for the vacuum annealed samples. While maintaining a high spin polarization, the resistivity, which is determined by the barrier width and height in Fe3O4 films, can be tuned over three orders of magnitude at room temperature by annealing. Resistivity over seven orders of magnitude is obtained from 108 to 300 K, which enables the nanocrystalline Fe3O4 to be a versatile spin injector matching with various doped semiconductors with different conductivities, and makes it a possible candidate for high-efficient magnetoelectronic devices.