Stabilization of surface magnetism by organic-acid adsorption
ORAL
Abstract
Magnetically-disordered layers at the surface of nanoparticles and low dimensionality magnetic oxides significantly reduce the magnetization density with respect to bulk values. However, high crystal quality Fe$_3$O$_4$ nanoparticles capped with non-magnetic organic acid molecules display a surprisingly high magnetization, of unknown origin. Here, we present a real space structural, chemical and magnetic characterization of oleic-acid-caped Fe$_3$O$_4$ nanoparticles with nanometer resolution, demonstrating the presence of a strong magnetic surface layer. In combination with theoretical calculations, we establish the key role of the nanoparticle/organic-acid bond. Magnetization is restored in the surface layer because the bonding with the acid's O atoms partially lifts the surface reconstruction, resulting in surface O-Fe atomic configuration and distances close to the bulk values. Our findings have implications for the optimization of magnetic properties of nanoparticles and thin films.
*Acknowledgements: European Research Council Starting Investigator Award program (JS, JG), Spanish MICINN and Catalan DIUE (NP, AL, XB) and the U.S. Department of Energy, Office of Basic Energy Sciences, Materials Sciences and Engeering Division (MV, SJP).
–