TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preparation (Claimed): Preparation of core-shell nanoparticles comprises producing iron core particles by reducing an iron salt using a reducing agent; and forming a nickel shell on the iron core particles. Preferred Components: The core component includes nickel, oxygen, iron and/or boron. The atomic ratio of nickel and iron in the core component is 0.7:1-1.2:1, preferably 0.4:1-1.2:1. The shell component includes iron, nickel and/or oxygen. The shell component includes a first shell and a second shell. The first shell is disposed between the core and the second shell. The first shell and the second shell include the nickel. The nanoparticles have an average outer span range of 5-500 nm, preferably 50-200 nm. The iron salt is iron sulfate heptahydrate (FeSO4x 7H2O). The molar ratio of phosphonate stabilizer to iron is 0.05:1-0.8:1. The reducing agent is sodium borohydride (NaBH4). The molar ratio of sodium borohydride to iron is 2.2-2.5:1. The nickel salt is nickel chloride hexahydrate (NiClx 6H2O). The molar ratio of polyvinyl pyrrolidone and carboxymethyl cellulose to nickel is 0.0005:1-0.05:1. The molar ratio of at least one of amino tris (methylene phosphonic acid) and diethylenetriamine penta(methylene phosphonic acid) to nickel is 0.05:1-0.8:1. The molar ratio of nickel salt to iron is 0.5:1-2000:1. Preferred Method: The nickel shell forming step is performed by forming an aqueous suspension of the iron core particles and adding nickel salt to the suspension. The iron core particles producing and nickel shell forming steps are performed using stabilizing agent in an aqueous system during the reducing of the iron salt. The method further comprises combining the iron-nickel core-shell nanoparticles with ethanol.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Components: The stabilizer agent is amino tris (methylene phosphonic acid), diethylenetriamine penta(methylene phosphonic acid) (both preferred), polyvinyl pyrrolidone and/or carboxymethyl cellulose. EXAMPLE - None given.