An in situ process for preparing a phase change magnetic ink including heating a phase change ink composition to a first temperature sufficient to provide a melt composition; wherein the phase change ink composition comprises a carrier, an optional colorant, and an optional dispersant; placing the melt composition under inert atmosphere; heating the melt composition to a second temperature sufficient to effect decomposition of a metal carbonyl; adding the metal carbonyl to the melt composition under inert atmosphere at this second temperature to form metal nanoparticles thus forming in situ a phase change magnetic ink including the metal nanoparticles; optionally, filtering the phase change magnetic ink while in a liquid state; and cooling the phase change magnetic ink to a solid state.