Nanocrystalline NiFe2O4 was synthesized using high-energy ball milling. The effect of milling time on structural and magnetic properties was investigated. X-ray diffraction results revealed a progressive transformation from mixed NiO-Fe2O3 precursor phases to a single-phase cubic spinel NiFe2O4 structure with crystallite sizes ranging from 33.64 to 41.17 nm. The scanning electron microscopy showed small grains attaching to big grains for 1 h milled sample. The big grains disappear with increasing milling time. Homogeneous nanoparticles, spherically shaped and agglomerated nanoparticles, were observed for samples that were milled for 5, 10, and 15 h. Energy-dispersive X-ray spectroscopy confirmed the presence of all expected elements. The nature of M-H loops for all the samples shows soft ferromagnetic behavior. The Electron spin resonace (ESR) results revealed the reduction of resonance field with increasing milling time. The g-values increased with milling time. The obtained high g-values make NiFe2O4 oxides suitable for applications in high-frequency devices. The spin-spin (τ1) relaxation time decreased with increasing milling, time while the spin-lattice (τ2) showed improvement.
Dlamini et al. (Thu,) studied this question.