Magnetic characterization of nanocrystalline Ni-Zn ferrite powder prepared by the glyoxylate precursor method

Nanocrystalline Ni0.35Zn0.65Fe2O4 mixed ferrite was obtained from the Fe-2(Ni-0.35,Zn-0.65)(OH)(4)(C2H2O4)(2) . H2O complex combination that corresponds to the atomic ratio Ni(II): Zn(II): Fe(III) = 0.35: 0.65: 2; the complex combination was decomposed at 325degreesC and the resulting oxides mixture was annealed in the temperature range of 400-1000degreesC for 2 h. The thermal analysis of the synthesized complex combination was done by TG-DTA techniques. It has been shown by means of x-ray diffraction that even at 400degreesC Ni-Zn mixed spinel ferrite is formed with an face-centred cubic structure and a lattice parameter that is in agreement with the reported value. Thus, the formation temperature of ferrite was drastically reduced (by cca. 900degreesC) compared to that of the conventional ceramic method. The magnetic measurements showed the increase of the saturation magnetization sigma(s) and a maximum of the coercivity H-c of the nanocrystalline system with the increase of the annealing temperature. These changes can be attributed to the increase of the average diameter of the nano-sized crystallites from 14.6 to 46.3 nm when the temperature increases from 400degreesC to 1000degreesC. The nanocrystallites are single-domain up to similar to28 nm; above this value they have an incipient structure of Weiss domains, a result that is in agreement with the critical diameter of the single-domain deduced from theoretical calculation.