This dataset contains the comprehensive research results associated with the article "Synthesis and investigation of Mg–Fe nanocomposites formed by decomposition of ternary magnesium-iron hydride". The provided data supports the characterization of the synthesized nanocomposites, examining their structural, thermal, mechanical, and magnetic evolution during the hydride decomposition process. The database includes the following research data and experimental results: XRD Data: X-ray diffraction patterns confirming the phase composition, crystal structure, and successful decomposition of the ternary magnesium-iron hydride. DSC/TG Curves: Differential Scanning Calorimetry and Thermogravimetry profiles illustrating the thermal stability, decomposition pathways, and mass changes of the samples. Nanoindentation Profiles: Mechanical testing data detailing the hardness and reduced elastic modulus of the resulting Mg–Fe nanocomposites. SEM/STEM Micrographs: High-resolution Scanning and Transmission Electron Microscopy images revealing the morphology, microstructure, and nanoscale distribution of the iron and magnesium phases. Magnetic Property Plots: Magnetization curves (including hysteresis loops) characterizing the magnetic behavior and properties of the obtained nanocomposites.