Spin-dependent intergranular transport in magnetite films deposited by ferrite plating

The present article describes that Fe3-xO4 films prepared by the ferrite plating exhibited negative magnetoresistance associated with spin-dependent intergranular transport. The Fe3-xO4 plated films were composed of Fe3O4 and gamma-Fe2O3; the relationship between the degree of oxidation, magnetic and electrical properties by changing the concentration of NaNO2 in the oxidizing solution C-NaNO2 was discussed. Current-in-plane (CIP) electrical properties were investigated with a four-probe method at room temperature. Resistivity was about 2-200 Omega cm, which is higher than that of bulk magnetite (10(-2) Omega cm). Negative magnetoresistance with peaks at the coercive field was observed and the MR ratios taken in the maximum field of 2.5 kOe increased up to 5.5% with increasing C-NaNO2. Mossbauer spectroscopy and the electrical evaluation showed that an increase in the Fe3+ ion content, in other words, an increase in insulating region raised the resistivity of the films with increasing C-NaNO2. The dependence of the MR ratio on C-NaNO2 suggested that such insulating region existed in the grain boundaries and the MR effect was caused by the spin-dependent intergranular transport of electrons through the insulating regions. The results suggest that appropriate control of the gain boundaries through changing the oxidizing conditions enables us to improve the MR effect. (C) 2000 American Institute of Physics. [S0021-8979(00)67208-0].