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Resistive-based gas sensors have been examined as the most favourable gas sensors for toxic gases and volatile organic compounds owing to their low cost, ease of use, high stability and simple structure. In this work, ammonia gas sensing self-assembled nanostructure material Ni0.5ZnxMg0.5−xFe2O4 (x = 0.00, 0.15, 0.30, 0.45) were successfully synthesized by the modified solution combustion method and examined for the structural, morphological, dielectric and gas sensing properties by X-ray diffraction, field emission scanning electron microscopy, impedance analyzer and the gas sensing setup. The dielectric properties were enhanced by Zn2+ doping. The ammonia vapour sensor based on Ni0.5ZnxMg0.5−xFe2O4 (x = 0.00, 0.15, 0.30, 0.45) shows interesting p-type behaviour gas sensing characteristics at the operational temperature of 300 K. The response to 50 ppm ammonia is 576%, 538%, 423% and 467% for x = 0.00, 0.15, 0.30, 0.45 compositions of Ni0.5ZnxMg0.5−xFe2O4 respectively while as the response and recovery time for all compositions, is in the range of 50–58 s and 64–83 s respectively. Moreover, the ammonia (reducing gas) gas sensing mechanism is also presented. The observed interesting results like sensor response and selectivity propose that the self-assembled Ni0.5ZnxMg0.5−xFe2O4 can be assuredly applied in ammonia vapour detection. [ABSTRACT FROM AUTHOR]