Negative magnetoresistance in iron doped TiN thin films prepared by reactive magnetron sputtering

Iron doped titanium nitride thin films were prepared by RF/DC magnetron sputtering of titanium and iron targets in the presence of argon and nitrogen gasses. Iron concentration in the films was controlled by adjusting the DC power of the sputtering gun whereas the RF power for the titanium target was kept constant for all the films. Spectrophotometry of the grown films revealed a reduction in the bandgap with the increase in the iron concentration in the films. X-ray photoelectron spectroscopy of the films confirmed the presence of iron and the increase in its concentration with the increase in the DC sputtering power. The surface roughness of the films slightly increased with the increase in the iron concentration. All the grown films were n-type semiconductors and the carrier concentration increased with the increase in iron concentration. Positive magnetoresistance was observed in undoped or low-doped titanium nitride films, whereas negative magnetoresistance was observed in the films with high iron concentration, which was due to the formation of ferromagnetically aligned magnetic polarons.