Mukherjee S, Acharya S, Das D, Chakrabarti P K
Solid State Research Laboratory, Department of Physics, Burdwan University, Burdwan 713104, West Bengal, India.
J Nanosci Nanotechnol. 2010 Sep;10(9):5623-33. doi: 10.1166/jnn.2010.2469.
Nanocrystalline NiFe2O4 with different particle sizes and nanocomposites of (NiFe2O4)(1-x)(Al2O3)x (x = 0.25, 0.40) were prepared by using co-precipitation method. In this method two techniques viz., 'ultrasonication' and 'magnetic stirring' during co-precipitation were used. The as prepared samples were annealed at different temperatures to obtain samples with different particle sizes. The formation of the nanocrystalline spinel phases of all the samples were confirmed by X-ray diffraction (XRD) patterns. The sizes of the nanoparticles of all the samples were calculated from the broadening of the (311) line in the XRD pattern. The distribution of sizes are remarkably less in samples obtained from 'ultrasonication' technique compared to those obtained in 'magnetic stirring' technique. The different soft magnetic quantities viz., coercive field, magnetization, remanance, hysteresis losses etc. were extracted from the ac hysteresis loops observed at different frequencies. The variations of coercive field and hysteresis loss as functions of frequency and particle sizes have been studied. Mössbauer spectra of the samples along with the hysteresis loops recorded at room temperature indicate the presence of superparamagnetic (SPM) relaxations of the nanoparticles. Also, SPM relaxations have been introduced in the samples annealed at higher temperature by encapsulating the nanoparticles in non-magnetic matrix of Al2O3 with 40% coating.
