Multifunctional As4S4/Fe3O4 nanocomposites prepared by high-energy mechanical milling are probed by complementary methods of positron annihilation lifetime (PAL) spectroscopy, supported by microstructure characterization using X-ray powder diffraction (XRPD) with analysis applied to the first sharp diffraction peak (FSDP), morphology studies by transmission electron microscopy (TEM) with energy-dispersive spectroscopy (EDS) and high-resolution TEM (HRTEM). 
These nanocomposites are shown to consist of Fe3O4 crystallites with particle sizes of 8-21 nm, and far separated beta-As4S4 crystallites surrounded by amorphous As-S phase. In respect to PAL data, the effect of milling is identified as possible conversion from Ps traps to positron-trapping sites depending on preferential chemistry of atomic surrounding. So, the interfacial triple junctions at the intersections of Fe3O4 crystallites are identified as principal positron traps in As4S4/Fe3O4 nanocomposites with competitive influence from free-volume defects of amorphous As-S phase.