Abstract <p>The standard double sintered ceramic process utilized to synthesize Sm³⁺ substituted nickel copper ferrites with chemical formula Ni_0.5Cu_0.5Sm_<i>x</i>Fe_2–<i>x</i>O₄ with (<i>x</i> = 0.1, 0.2, 0.3). The X-ray diffraction studies, which verify the presence of a single phase, same is used to determine the particle size. The Debye Scherer formula is employed to calculate the magnitude of crystallites for high intensity peak (3 1 1). The elemental composition is examined by energy dispersive spectroscopy, the constituent elements of developed samples is confirmed. Two absorption bands are developed subsequently by interatomic vibrations in the locations of the tetrahedral and octahedral of the current samples. These bands are identified in the spectrum obtained by fourier transform infrared spectroscopy. The optical band gap is estimated and are found in the range of 2.14 to 2.55 eV, it shows the ferrites are in semiconducting nature. There will be an increase in the saturation magnetization (<i>M</i>_s), coercive field (<i>H</i>_c) and retentivity (<i>M</i>_r) along with a rise in the substitution of Sm³⁺. The gas sensing characteristics of properties of Sm³⁺ substituted nickel copper ferrites are studied for different ppm of NO₂ gas.</p>