Publication: Structure and magnetism of ultrathin nickel-iron oxides grown on Ru(0001) by high-temperature oxygen-assisted molecular beam epitaxy
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We demonstrate the preparation of ultrathin Fe-rich nickel ferrite (NFO) islands on a metal substrate. Their nucleation and growth are followed in situ by low-energy electron microscopy (LEEM). A comprehensive characterization is performed combining LEEM for structural characterization and PEEM (PhotoEmission Electron Microscopy) with synchrotron radiation for chemical and magnetic analysis via X-ray Absorption Spectroscopy and X-ray Magnetic Circular Dichroism (XAS-PEEM and XMCD-PEEM, respectively). The growth by oxygen-assisted molecular beam epitaxy takes place in two stages. First, islands with the rocksalt structure nucleate and grow until they completely cover the substrate surface. Later three-dimensional islands of spinel phase grow on top of the wetting layer. Only the spinel islands show ferromagnetic contrast, with the same domains being observed in the Fe and Ni XMCD images. The estimated magnetic moments of Fe and Ni close to the islands surface indicate a possible role of the bi-phase reconstruction. A significant out-of-plane magnetization component was detected by means of XMCD-PEEM vector maps.
©2018 Nature Publishing Group This work is supported by the Spanish Ministry of Economy and Competitiveness through Projects No. MAT2014-52477-C5-2-P, MAT2015-64110-C2-1-P, and MAT2015-64110-C2-2-P and by the European Comission through Project H2020 No. 720853 (Amphibian). These experiments were performed at the CIRCE beamline of the ALBA Synchrotron Light Facility. A. M. acknowledges funding via a CSIC-Alba agreement. This work would not have been possible without the support of Jordi Prat.