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

Abstract

Nanocrystalline Ni0.35Zn0.65Fe2O4 mixed ferrite was obtained from the Fe2(Ni0.35,Zn0.65)(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 325°C and the resulting oxides mixture was annealed in the temperature range of 400–1000°C 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 400°C 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. 900°C) compared to that of the conventional ceramic method. The magnetic measurements showed the increase of the saturation magnetization σs and a maximum of the coercivity Hc 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 400°C to 1000°C. The nanocrystallites are single-domain up to ∼28 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.