Substitutional effect of Mg2+ on structural and magnetic properties of cobalt nanoferrite

Abstract This work focuses on the study of structural and magnetic properties of Mg2+-substituted cobalt nanoferrite (Co1-xMgxFe2O4, 0.0 ≤ x ≤ 1.0). The samples were synthesized by a coprecipitation route and then annealed at 850 °C for 2 h under atmospheric air. The X-ray diffraction patterns show that the samples crystallize in a cubic spinel structure with space group F d 3 ¯ m , and 3% secondary phase was identified as hematite ( R 3 ¯ c ) for x = 1.0. The average crystallite size (D) and the lattice parameter were greatly influenced by Mg content (D decreased from 38 to 20 nm). Transmission electron microscopy investigations revealed that the grains have an almost spherical shape and furthermore that the samples are chemically homogeneous. Magnetic measurements at 5 K revealed a wasp-waist magnetic hysteresis behavior of Co–Mg ferrite. The coercivity of Co0.4Mg0.6Fe2O4 with D = 25 nm was enhanced, with a maximum value of 4000 Oe. The room temperature Mossbauer spectra were fitted with two Zeeman sextets, which reflects the incorporation of Fe3+ in the A and B sublattices of the spinel structure. The hyperfine field of these sites decreases similarly to the saturation magnetization with increasing Mg content. The spectrum corresponding to x = 1.0 was calculated with the help of the hyperfine field distribution. Moreover, Mossbauer spectra, fore x = 0.0 and 1.0 were recorded at 6 and 80 K and were adjusted by the superposition of three sextets: one sextet for the A site and two sextets for the B sites (B1 and B2). The hyperfine parameters such as the hyperfine field and the isomer shift were improved at 6 and 80 K.