Mediating the exchange coupling and anisotropy in nanoscale magnets via interfacial interactions
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Nanoscale materials behave differently than their bulk counterparts due, in part, to the reduced length scales and the increased surface to core atom ratio. As the length scales decrease, the surface atoms become increasingly important as they make up a larger percentage of the total number of atoms. These surface atoms have magnetic properties that differ from the core atoms due to a surface anisotropy that alters the interparticle, intraparticle, and exchange interactions. In this work, we have synthesized three different nanoscale systems that will allow us to explore the physics of the different interactions. Cu/gamma-Fe2O3 core/shell nanoparticles were chosen because the gamma-Fe2O3 cores have vacancies in their B-sites, broken coordination at the surface, and experience superexchange interactions. As a comparison, multiphase undoped and V-doped SiO2/FeCo nanoparticles were chosen as these nanoparticles do not suffer from vacancies or surface disorder and experience both direct exchange interactions from the nanoparticle core and superexchange interactions between the FeCo core and the metal silicate interfacial phase. Finally, Fe nanocrystallites were grown in a Cu matrix as they present no vacancies or surface disorder, and they are single phase. We observed that the interfacial phases that form in these core/shell and nanocrystallite/matrix nanoscale systems alters significantly the physics of the magnetism. The overall magnetic properties, the elemental magnetism, and the atomic magnetism were all observed to be altered by this interfacial phase, along with the interparticle and intraparticle interactions. In addition, the thickness of this interfacial phase, and thus the strength of its affect, was controlled by controlling the thickness of the shells or the amount of intermixing in the case of the nanostructured thin film.