Exchange bias effect in Au-Fe3 O4 dumbbell nanoparticles induced by the charge transfer from gold

Mikhail Feygenson, John C. Bauer, Zheng Gai, Carlos Marques, Meigan C. Aronson, Xiaowei Teng, Dong Su, Vesna Stanic, Volker S. Urban, Kevin A. Beyer, Sheng Dai

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24 Scopus citations

Abstract

We have studied the origin of the exchange bias effect in the Au-Fe3O4 dumbbell nanoparticles in two samples with different sizes of the Au seed nanoparticles (4.1 and 2.7 nm) and same size of Fe3O4 nanoparticles (9.8 nm). The magnetization, small-angle neutron-scattering, synchrotron x-ray diffraction, and scanning transmission electron microscope measurements determined the antiferromagnetic FeO wüstite phase within Fe3O4 nanoparticles, originating at the interface with the Au nanoparticles. The interface between antiferromagnetic FeO and ferrimagnetic Fe3O4 is giving rise to the exchange bias effect. The strength of the exchange bias fields depends on the interfacial area and lattice mismatch between both phases. We propose that the charge transfer from the Au nanoparticles is responsible for a partial reduction of the Fe3O4 into the FeO phase at the interface with Au nanoparticles. The Au-O bonds are formed, presumably across the interface to accommodate an excess of oxygen released during the reduction of magnetite.

Original languageEnglish
Article number054416
JournalPhysical Review B - Condensed Matter and Materials Physics
Volume92
Issue number5
DOIs
StatePublished - Aug 10 2015

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