FeCo is a material attracting the interest of many because its very high saturation magnetization (up to 2.45 T). In this study, FeCo nanoparticles assembled films with a matrix (carbon) were prepared by an integrated nanocluster deposition system with a gas aggregation cluster source and dc magnetron co-sputtering guns. The nanoparticles are produced from a Fe65 Co35 alloy target. The average particle size is controlled to vary from 5 to 12 nm. The size distribution is less than 10%. Transmission electron microscope images show the change of crystallinity upon online heating. FeCo nanoparticles with cubic shape are formed with online heating. Hc is found to increase with the carbon matrix deposited.