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Rare earth Neodymium (Nd 3+ ) doped nanocrystalline Ni-Co mixed spinel ferrites which are chemically represented as Ni 0.5 Co 0.5 Nd x Fe 2-x O 4 (x = 0.025 to 0.125, in the step of 0.025) were synthesized by sol-gel auto-combustion method. The structural, morphological, infrared and magnetic properties were studied in detail in the light of Nd 3+ doping using standard techniques. X-ray analysis reveals the formation of single phase cubic spinel structure for all the prepared samples without any impurity phase. The crystallite size calculated from Scherrer's formula was observed to be decreasing with increasing Nd 3+ content. The lattice parameter calculated using XRD data was found to be decreasing upto x = 0.100 and then increases for x = 0.125. X-ray density was observed to be increasing from 5.327 to 5.630 gm/cm 3 . Surface morphology was studied through scanning electron microscopy technique. Grain size calculated from SEM analysis was found to be in the range of 30–59 nm. From transmission electron microscopy study, the average particle size was observed to be in the range of 35–45 nm. FTIR results exhibit the characteristics cubic spinel ferrite nature of the samples with two prominent absorption bands near 400 cm −1 and 600 cm −1 . FTIR also confirms the incorporation of Nd 3+ in the crystal structure. The magnetic behavior shows strong influence of substitution of Nd 3+ ions. The saturation magnetization, coercivity and remenance magnetization all decrease with substitution of Nd 3+ ions up to x = 0.100. For further increase in Nd 3+ concentration (x = 0.125), the saturation magnetization found to be increased. [ABSTRACT FROM AUTHOR]