Magnetic properties of nanosized Gd doped Ni–Mn–Cr ferrites prepared using the sol–gel autocombustion technique

• Gd doped Ni–Mn–Cr ferrites were obtained using the sol–gel autocombustion technique.
• XRD and IR analysis reveals the pure spinel structure.
• Average grain size decrease with Gd-content.
• Saturation magnetization, coercivity and Curie temperature decrease with Gd doping.

Ni0.8Mn0.2Cr0.5Fe1.5-xGdxO4 (where x=0, 0.02, 0.04, 0.06, 0.08) spinel ferrites were synthesized by a sol–gel autocombustion technique using citric acid as fuel. Effect of Gd doping on structural and magnetic properties of Ni–Mn–Cr ferrites is reported. The phase composition of the prepared samples was analyzed by X-ray diffraction and Fourier transform infrared spectroscopy, and the magnetic measurements were realized using a vibrating sample magnetometer. XRD and FT-IR analysis reveal pure spinel phase in all the samples, without traces of secondary phases. The grain sizes were estimated from the TEM micrographs and were found to decrease with the doping ions concentration from 43 to 10 nm. It was revealed from the hysteresis loop of the materials that magnetization and coercivity followed decreasing trend with substitution of Fe3+ magnetic ions by Gd3+ ions. Also, introducing Gd ions into the spinel lattice led to the decrease in Curie temperature.