Morphology, Structural Control, and Magnetic Properties of Carbon-Coated Nanoscaled NiRu Alloys

Carbon-coated nanoparticles of NiRu (NiRu@C) have been synthesized by a high-pressure chemical vapor deposition using metallocenes of both metals. Transmission electron microscopy images show an average particle size (core) of 8 +/- 3 nm and carbon shell thicknesses between 2 and 3 nm. X-ray diffraction investigation reveals NiRu binary alloys. Analyses of the X-ray diffraction peaks and the magnetization curves approximately confirm the average particle size. The compositions of the nanoalloy cores have been studied by means of energy dispersive X-ray analysis. We find that at constant sublimation temperature (95 degrees C) a synthesis temperature of 900 degrees C and a Ni-Ru-metallocene weight ratio of 2:1, an increase of synthesis pressure leads to both a change of the core composition and the thickness of the carbon coatings. The magnetic properties of the coated nanoalloys strongly depend on the synthesis parameters so that, for example, the superparamagnetic blocking temperature and the saturation magnetization can be tailored. Our straightforward of controlled synthesis therefore opens a novel route to complex nanosized functional materials.