The present work reports on the low-pressure, radio-frequency, plasma-driven synthesis of ε-Fe3N-type nanoparticles homogeneously deposited on a high-surface-area porous carbon support, with tunable magnetic properties, directly depending on the plasma treatment conditions. Iron nanoparticles are formed from the degradation of a solid organometallic precursor mixed with a carbon xerogel in a nitrogen-containing (argon/ammonia) plasma discharge. Variation of the working pressure during the plasma treatment directly affects the residence time of the reactive species, which determines the crystalline state of the nanoparticles, from amorphous at low-pressure treatment to well crystallized at high-pressure treatment. This results in a direct influence of the magnetic properties of the iron nitride nanoparticles. The working pressure results in two competing effects because it enhances the crystallinity (at higher pressure) and also slightly affects the surface chemistry of the nanoparticles by increasing the oxygen content, while the last is believed to deteriorate the magnetic properties; however, the crystallinity enhancement dominates. The synthesized FexN/CXG magnetic composites have been applied as filler materials in alginate membranes for ethanol dehydration in a pervaporation experiment. Results indicate a considerably enhanced performance of the alginate membrane as determined by its selectivity, the separation index, and the flux even when using a small FexN/CXG loading (3% w/w).