Evidence for largest room temperature magnetic signal from Co2+ in antiphase-free & fully inverted CoFe2O4 in multiferroic-ferrimagnetic BiFeO3-CoFe2O4 nanopillar thin films

• Published in: Journal of magnetism and magnetic materials Vol. 530; p. 167940
• Main Authors: Wang, Xiao, Hu, Zhiwei, Agrestini, Stefano, Herrero-Martín, Javier, Valvidares, Manuel, Sankar, Raman, Chou, Fang-Cheng, Chu, Ying-Hao, Tanaka, Arata, Tjeng, Liu Hao, Pellegrin, Eric
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 15-07-2021; Elsevier BV
• Subjects: Bismuth ferrite; Cobalt ferrite; Cobalt ferrites; Dichroism; Heterostructures; Magnetic moments; Magnetic properties; Magnetic signals; Multiferroic; Multiferroic materials; Nanopillars; Optimization; Room temperature; Self-assembly; Soft x rays; Spectrum analysis; Spinel; Spintronics; Thin films; X ray absorption; XMCD; Nanopillars; Spinel; Cobalt ferrite; XMCD; Multiferroic; Spintronics
• ISSN: 0304-8853; 1873-4766
• DOI: 10.1016/j.jmmm.2021.167940

•Antiphase-free and full inverted nanopillar thin films of cobalt ferrite inverse-spinel was obtained.•The largest x-ray magnetic circular dichroism signal of divalent cobalt at room temperature was observed.•X-ray absorption spectra and x-ray magnetic circular dichroism spectra were nicely reproduced by full atomic multiplet theory.•The enhanced performance of the cobalt ferrite inverse-spinel nanopillar thin film plausibly comes from its appropriate size.
The ongoing quest for defect-free thin films systems that are apt for being used as spin filtering materials for spintronic applications did yet not deliver satisfying results regarding materials that would be up to the pertinent requirements. Using soft x-ray absorption spectroscopy (XAS) and x-ray magnetic circular dichroism (XMCD) measurements at the Co-L2,3 and Fe-L2,3 absorption edges, we have investigated the magnetic properties of a nanostructured thin film with self-assembled CoFe2O4 nanopillars embedded in BiFeO3, the latter being a well-known system for its combined multiferroic and spintronic properties. In this BiFeO3-CoFe2O4 heterostructure we observed a significant XMCD signal at the Co-L2,3 edges which turns out to be the largest among the presently reported for Co ions at room temperature. A quantitative analysis of the Co-L2,3 spectra unveils that such a large Co-L2,3 XMCD signal stems from the impeccable fully inverted spinel ordering of the A- and B-sites in antiphase-free CoFe2O4 nanopillars. This twofold perfect CoFe2O4 ordering feature yields an unprecedented optimization within a multifunctional ferrimagnetic-multiferroic thin film system highly relevant for spintronic applications, also resulting in an equally unprecedented macroscopic magnetic moment for such material as compared to its pure form as well as to technologically relevant thin film compound systems.