FORC investigation of Co-Ni bulk ferrite consolidated by spark plasma sintering technique

摘要

Bulk samples of Co_(1-x)Ni_xFe_2O_4 (x = 0.0, 0.2, 0.4, 0.6, 0.8 1.0) were shaped by a spark plasma sintering (SPS) process. The initial ferrite nano-powders which were prepared using a co-precipitation method were characterized by high-resolution transmission electron microscopy (HRTEM) and Mossbauer spectroscopy. The HRTEM showed nanoparticles with almost 5-35 nm average size. Mossbauer spectrometer is employed to study the magnetic properties of ferrite nano-powders at room temperature. X-ray diffractometer (XRD), field emission scanning electron microscopy (FESEM) coupled with EDS detector for the chemical composition analysis and vibration sample magnetometer (VSM) equipped with FORC software were used to characterize the bulk samples. Without any structural changes to powder samples, a single-phase spinel structure was obtained. In the FESEM micrograph, the porosity decrease and consequently the density increase are clearly visible and the EDS study confirms the presence of Fe, Co, Ni and O ions in the fabricated samples by SPS process. The magnetic parameters such as saturation magnetization and the coercivity showed a decreasing behavior with an increase in Ni concentration from 67 emu/g and 787 Oe to 42.77 emu/g and 151 Oe, respectively. FORC analysis implies the coercivity reduction of bulk samples comparing with powders state in cobalt-rich ferrites is due to the multi-domain formation. The coercivity unavoidable in nickel-rich ferrites is due to the occurrence of the multi-domain state along with the disappearance of the superparamagnetic phase.