Low-field positive and high-field negative magneto-resistances in multiphase Fe-oxide thin films at room temperature
Low-field positive and high-field negative magnetoresistances in multiphase Fe-oxide thin films at room temperature

Multiphase Fe-oxide thin films are fabricated on glass substrates by a facing-target sputtering technique. X-ray diffraction and X-ray photoelectron spectroscopy reveal that Fe, Fe3O4, γ-Fe2O3 and FeO coexist in the films. High resolution transmission electron microscopy shows the well-defined columnar grain structure with the unoxidized Fe as the core and iron-oxide as the shell. The low-field positive and high-field negative magnetoresistances coexist in such a system at room temperature, which can be explained by considering a shell/core model. Nonlinear current-voltage curve and photovoltaic effect further confirm the tunneling-type conduction. Supported by the National Natural Science Foundation of China (Grant Nos. 50672132 and 60576015) and the Key Project of Chinese Ministry of Education (Grant No. 107020)