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

Nanocrystalline Ni 0.35 Zn 0.65 Fe 2 O 4 mixed ferrite was obtained from the Fe 2 (Ni 0.35 ,Zn 0.65 )(OH) 4 (C 2 H 2 O 4 ) 2 ⋅H 2 O 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 σ 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 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.