Nitrogen (15N) and carbon (12C) ion implantations with implant energy of 100 keV for different doses were performed on nanosized diamond (ND) particles. Magnetic measurements on the doped ND show ferromagnetic hysteresis behavior at room temperature. The saturation magnetization (M(s)) in the case of 15N implanted samples was found to be higher compared to the 12C implanted samples for dose sizes greater than 10(14) cm(-2). The role of structural modification or defects along with the carbon-nitrogen (C-N) bonding states for the observed enhanced ferromagnetic ordering in 15N doped samples is explained on the basis of x-ray photoelectron spectroscopy measurements.

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Sb-doped FePt nanoparticles with an average diameter of 8.5 nm were prepared by thermal decomposition of platinum acetylacetonate, antimony acetate, and iron pentacarbonyl. Upon annealing to ϳ300 °C for 30 min, nanoparticles with X Sb = 0.14 and 0.23 show H c Ͼ 500 mT, and L1 0 ordering parameter S values of ϳ0.83-0.87. Transmission electron microscopy of the annealed assemblies shows no observable nanoparticle coalescence at 300 °C. Low-temperature coercivity measurements with a superconducting quantum interference device indicate the presence of particles that exhibit superparamagnetism, probably due to the large particle size distribution or inhomogeneity in Sb incorporation. Our results underscore the necessity to synthesize monodisperse FePt nanoparticles with controlled composition to maximize ferromagnetic behavior.