For the first time, rare earth doped strontium hexaferrite nanoparticles Sr_(1−x)La_xGd_ySm_zFe_(12−(z+y))O₁₉ (x = 0.3, y = z = 0.01) were synthesized by the sol–gel combustion method in this paper. A single-phase with space group P63/mmc was confirmed by X-ray diffraction (XRD) and the average crystallite size was found to be 46 nm. The existence of absorption bands of the hexaferrite phase structure was shown by the Fourier transform infrared (FT-IR) spectra. Raman analysis confirms the formation of all crystallographic hexaferrite sites. The effect of the rare earth elements on the nanoparticles’ morphology was evaluated by scanning electron microscopy (SEM) analysis. Energy-dispersive X-ray spectroscopy (EDX) results confirm the sample homogeneity. The value of the band gap was found to be 1.52 eV from the UV-vis NIR spectra. The magnetic analysis of the prepared sample revealed at room temperature a coercivity, saturation magnetization, remanence ratio, maximum magnetic energy product, switching field distribution, and a Curie temperature of 4296.39 Oe, 62.29 emu g⁻¹, 0.49, 7.79 KJ m⁻³, 0.663, and 490 °C, respectively. These results suggest that this material has a significant function in industry, which could be beneficial for recording media applications. Using first-principles calculations, the site preference of the doping elements Sm, Gd, and La, as well as the effect of doping with these elements on the structural, magnetic, and electronic properties of the M-type strontium hexaferrite, was investigated.