Nominal [Fe(t)/Ir(t′)]n (M/M type), [FeOx(t)/IrOx(t′)]n (O/O), and [Fe(t)/IrOx(t′)]n (M/O) multilayers have been prepared by magnetron sputtering at room temperature. Composition, structure, and magnetic behavior have been analyzed. In the M/M samples, the Fe and Ir phases are identified as bcc and fcc, respectively. The magnetism evolves from bulklike iron to granular behavior as the thickness of the Fe layers decreases. An induced magnetic moment, ferromagnetically coupled to Fe, is observed on Ir by x-ray magnetic circular dichroism (XMCD). Besides, the presence of negative remanent magnetization is observed in the M/M samples. As for the M/O samples, the stronger affinity of iron for oxygen displaces the oxygen atoms giving rise to actual heterostructures that strongly differ from the nominal ones. For similar thickness of the two layers the Fe layer become oxidized while a mixture of metal and oxide phases is found in the Ir layer. The increase of the Fe thickness leads to a metallic Ir layer and a highly coercive (∼4.4 kOe) core-shell metal-oxide structure in the Fe layers.

This work was partially supported by the Spanish Ministry of Economy and Competitiveness (MINECO) under contract Projects No. MAT2014-54425-R and No. MAT2017-83468-R by the Aragón DGA NETOSHIMA grant. E.A.-E. acknowledges the Spanish MINECO and the European Social Fund for a FPI (2015) grant. 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

Peer reviewed