[en] Highlights: • Uniform thin films assembled by Fe₃O₄-Ag composite nanoparticles were prepared. • Magnetoresistive devices were fabricated using the nanoparticle-assembled films. • Magneto-transport and electron-transport studies of the device were performed. • An enhanced MR ratio and a non-linear I–V relation were observed in the device. • The fabrication procedure can be extended to other composite nanoparticles. - Abstract: Controlled self-assembly of multi-component magnetic nanoparticles could lead to nanomaterial-based magnetic devices with novel structures and intriguing properties. Herein, self-assembled thin films of Fe₃O₄-Ag composite nanoparticles (CNPs) with hetero-dimeric shapes were fabricated using interfacial assembly method. The CNP-assembled thin films were further transferred to patterned silicon substrates followed by vacuum annealing, producing CNP-based magnetoresistive (MR) devices. Due to the presence of intra-particle interfaces and inter-particle barriers, an enhanced MR ratio and a non-linear current-voltage relation were observed in the device. The results of this work can potentially pave the way to the future exploration and development of spintronic devices built from composite nanomaterials.