Growth of the invar nanoparticles on the graphene oxide support

Binary nanoparticles, composed from two different metals, attract significant attention because they possess properties not typical for respective single-component nanoparticles. In bulk form, iron and nickel form an alloy called invar in which the two metals are mixed in the ratio Fe:Ni = 2:1. In this work, we demonstarte formation of the alloyed nanoparticles of invar, as opposed to the theoretically possible formation of the particles of the two individual metals. The formation of the alloyed nanoparticles is conducted in the two-step process: liquid phase impregntaion of graphene oxide with the salts of the metals, and sussequent annealing of the as-formed dry composite. Unlike the solution phase reaction conditions, in this approach, the binary nanoparticles are assembled in conditions, where the metals atoms are immobilized on the surface of the decomposing graphene oxide, and at temperatures significantly lower than the melting points of the two metals. The structure of the as-grown nanocrystals is investigated by Mossbauer spectroscopy, powder X-ray diffrcation, X-ray photoelectron spectroscopy, and scanning electron microscopy. Majority of the Fe/Ni nanoparticles are in a magnetically ordered state, and the composite is a soft magnet.