Structural and magnetic studies of nanocrystalline Mg-doped Li0.5Fe2.5O4 particles prepared by mechanical milling

H. WIDATALLAH; A. . M. GISMELSEED; C. JOHNSON; I. AL-OMARI; S. J. STEWART; S. H AL-HARTHI; S. THOMAS; H. SITEPU

JOURNAL OF PHYSICS - D (APPLIED PHYSICS)

Año: 2008 vol. 41 p. 165006 - 165016

0022-3727

The structure and magnetic properties of spinel-related Mg-doped Li0.5Fe2.5O4 nanocrystalline particles prepared by milling a pristine sample for different times were investigated. The lattice constant increased initially and later decreased whereas the infrared spectral bands of the material were found to shift with increasing milling time. These results imply strains, bond deformation and cationic migration at the nanoparticles’ surface layers. The surface to core volume ratio of the nanoparticles obtained from the Rietveld refinement of their x-raydiffraction data was used in a novel way to fit their 78K zero-field M¨ossbauer spectra. Thisoffered a simple tool to estimate the Fe3+ ionic distribution at the cores and surfaces of thenanoparticles without the need to use low-temperature in-field M¨ossbauer spectroscopy. Thesaturation magnetization and Curie temperature were found to decrease and the materialincreasingly turned superparamagnetic as milling proceeded. The coercivity and themagnetization increased initially and later decreased at higher milling times. The usefulness ofthe M¨ossbauer fitting approach adopted was demonstrated by using the Fe3+ ionic distributionobtained for the 50 h milled sample to calculate its magnetization in the framework of N´eel’scollinear model. The calculated value was found to be consistent with experiment if slightthermal spin reversal and/or canting effects are assumed.