The single phase Hf_xCe_1−xO₂ (x = 0.01, 0.05 and 0.1) nanoparticles were produced via microwave refluxing technique. The substitution of Hf-ions into CeO₂ lattice has been demonstrated by X-ray diffraction and transmission electron microscopy analyses. X-ray photoelectron spectroscopy analysis indicated that Ce was present in + 3 and + 4 states whereas Hf in + 4 state. Raman, UV–Vis and photoluminescence spectroscopic analyses revealed the formation of surface defects including oxygen vacancies in the samples. The estimated defect concentration was 1.09 × 10²¹, 1.32 × 10²¹ and 1.49 × 10²¹ cm⁻³ for x = 0.01, 0.05 and 0.1 samples respectively. The room temperature ferromagnetic behavior for the samples originate from the surface oxygen vacancies. The prevalence of ferromagnetic clusters considerably raised the MS value for x = 0.05 sample. The augmentation in the MS values with increased Hf concentration could be attributed to the increase in the defect concentration.