Growth and characterization of novel Ir1–xCrxO2 thin films

Novel Ir1–xCrxO2 thin films have been prepared by reactive co–sputtering deposition. Composition, structure and electric and magnetic behavior have been analyzed by different techniques including EDX, XRR, XRD, SQUID magnetometry, electrical resistivity and XANES and XMCD spectroscopies. Despite the difficulty in growing CrO2 by physical deposition techniques, an Ir1–xCrxO2 solid solution phase could be achieved for 0 ≤ x ≤ 0.8, where the oxidation state of Cr is found to remain as 4+. Both the electrical and the magnetic behavior are shown to starkly depart from those of the parent IrO2 (paramagnetic metal) and CrO2 (half–metal ferromagnet) compounds. In particular, they show a semiconducting behavior, dρ/dT < 0 and giant magnetic coercivity at low temperatures. XMCD reveals a significant contribution of Ir to the magnetic response of the Ir1–xCrxO2 films. In addition, the nature of the magnetic moment of the Ir4+ ion (〈ml〉/〈ms〉 = 0.09) is completely different from the large orbital moment that is a hallmark of insulating Ir4+ oxides. This suggests a Cr–induced magnetic moment, which is a remarkably surprising result for an oxide.