The synthesis of chromium doped Ni-Mg ferrite with a chemical formula Ni0.5Mg0.5Fe2-xCrxO4 (0 <= x <= 1.0 in a step of 0.2) was investigated in this study. The elemental analysis as obtained from energy dispersive X-ray (EDAX) is in close agreement with the expected composition from the stoichiometry of the reactant solutions used. X-ray diffraction (XRD) analysis reveals that all the samples posses a single phase cubic spinel structure. The lattice constant determined from XRD decreases with the Cr3+ substitution. The crystallite size estimated lies within the range of 30-35 nm. Field emission scanning electron microscopy (FE-SEM) and atomic force microscopy (AFM) confirm the homogeneous and well defined surface morphology of the synthesized samples. Fourier transform infrared spectroscopy (FT-IR) is employed to determine the local symmetry in crystalline solids and to shed light on the ordering phenomenon. Magnetization results obtained from the vibrating sample magnetometer (VSM) confirm that the substitution of Cr3+ for Fe3+ caused a decrease in the saturation magnetization from 29.78 to 5.88 emu/g and coercivity from 198.71 to 60.01 Oe. The dependence of the Mossbauer parameters, viz., line width, isomer shift, quadrupole splitting and hyperfine magnetic field on Cr3+ substitution have been analyzed. Neel's molecular field model is used to explain the variation of the hyperfine magnetic field with increasing Cr3+ substitution. (C) 2012 Elsevier B.V. All rights reserved.