Novel Ir1–xCoxO2 thin films: Growth and characterization

Ir1–xCoxO2 thin films have been prepared by reactive co–sputtering deposition at room temperature. Composition, structure, electronic properties and electric and magnetic behavior have been analyzed by different techniques including XRR, XRD, TEM microscopy, SQUID magnetometry, electrical resistivity and XAS spectroscopy. After annealing, an Ir1–xCoxO2 substitutional solid solution phase with rutile crystal structure was achieved for a wide Co-doping range 0 ≤ x ≤ 0.6. Starkly departing from the highly insulating behavior of CoO and Co3O4, the electrical resistivity at room temperature of our films is only slightly higher than that of IrO2. Likewise, our work shows that the magnetic response of the doped films is very similar to that of the paramagnetic parent IrO2. Neither ferromagnetism nor enhanced paramagnetism is observed. XAS spectra indicate a Co3+ oxidation state and, correspondingly, an oxidation state of ∼5+ for Ir ions in the polycrystalline Ir0.6Co0.4O2 film. By application of sum rules, a 13 % increase in the spin–orbit coupling is found despite the lattice shrinkage causes a detrimental bandwidth broadening