Effects of annealing on phase evolution, microstructure and magnetic properties of mechanically synthesized nickel-ferrite
Abstract The influence of milling and subsequent annealing on nickel-ferrite phase formation was investigated by X-ray diffraction (XRD). Microstructure and magnetic properties of NiFe 2 O 4 were determined by field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and vibration sample magnetometry (VSM). Single phase nanosized nickel-ferrite was obtained by 30 h mechanical alloying (MA) and subsequent annealing at 600 °C for 1 h. Magnetic properties of the milled powder were extensively affected by the annealing temperature. Considerable growth of the particles and necking by sintering resulted from annealing at 1000 °C.
Structural and magnetic properties of nanosize mechanosynthesized nickel ferrite
Abstract Nanocrystalline nickel ferrite (NiFe 2 O 4 ) with crystallite size ∼9 nm has been synthesized by high-energy milling method from a mixture of α-Fe 2 O 3 and NiO. Mossbauer spectroscopy, X-ray diffraction, transmission electron microscopy, and magnetization measurements have been used to investigate the structural and magnetic states of mechanosynthesized spinel ferrite. The observed reduction of the magnetization in nanoscale NiFe 2 O 4 is attributed to the mechanically induced non-equilibrium cation arrangement and to the canted spin configuration.
Comparative synthesize of nanocrystalline Fe–Ni and Fe–Ni–Co alloys during hydrogen reduction of NixCo1−xFe2O4
Abstract Nickel cobalt ferrite (NixCo1−xFe2O4) powder was prepared through the ceramic route by calcination of a stoichiometric mixture of nickel oxide, cobalt oxide and iron oxide. The produced powders of NixCo1−xFe2O4 were isothermally reduced in pure hydrogen at 800–1100 °C. Based on thermogravimetric analysis, the reduction behaviour of the synthesized ferrite and the kinetics reaction mechanism were studied. The initial ferrite powder and the various reduction products were characterized by XRD, SEM and reflected light microscope to reveal the effect of hydrogen reduction on composition, microstructure and magnetic properties of produced Fe–Nix–Co1−x alloy. Microstructure of partially and completely reduced samples was studied and the activation energy values were calculated from Arrhenius equation. The approved mathematical formulations for the gas solid reaction were applied to confirm the estimated rate controlling reaction mechanism. Complete reduction of NixCo1−xFe2O4 was achieved with synthesize of nanocrystalline Fe–Ni and Fe–Ni–Co alloys.