The magnetic properties of Ni0.7Mn0.3GdxFe2−xO4 ferrite

Nanocrystalline Ni0.7Mn0.3GdxFe2−xO4 ferrites were prepared by the emulsion method. The growth of particles, the structure and the magnetic properties were investigated by X-ray diffraction (XRD), Mössbauer spectroscopy and vibrating sample magnetometer (VSM). Furthermore, the influence of Gd2O3 on magnetic properties of Ni–Mn ferrite powders has been investigated in detail. When the crystallite sizes are about 30–40 nm, all the samples have similar Ms values. The variational rules of saturation magnetization (Ms) and coercivity (Hc) along with doped Gd contents at different sintering temperatures show that the maximum Gd ions content doped into ferrite lattices is x = 0.06. When Gd-doped content x is larger than 0.06, the doped Gd ions cannot enter into the ferrite lattice totally but reside at grain boundary, as the ionic radii of the Gd3+ ions are larger than that of Fe3+ ions. The ferrimagnetism has not disappeared completely, even if the crystallite size is 7.8 nm.