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.This work was partially supported by the Spanish Ministry of Science and Innovation under contract projects MAT2014–54425–R and MAT2017–83468–R. The authors would like to acknowledge the use of Servicio General de Apoyo a la Investigación–SAI, Universidad de Zaragoza. This research used resources of the APS, a US Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE–AC02–06CH11357. E.A.–E. acknowledges the Spanish MINECO and the European Social Fund for a FPI (Formación de Personal Investigador, 2015) grant.Peer reviewe