CRYSTALLITE SIZE DEPENDENCE ON THE MAGNETIC-PROPERTIES OF NANOCRYSTALLINE MAGNETITE POWDERS

Single phase magnetite powders with crystallite sizes ranging from 8-5 0 nm were synthesised and studied using X-ray diffraction and Mossbaue r spectroscopy. Lattice parameters were seen to decrease at very small crystallite sizes. Quadrupole splitting of the B sites increased with decreasing crystallite size before the spectrum collapsed into a doub let at the smallest sizes. These observations have been explained in t erms of high surface-to-volume ratios in the small nanocrystals creati ng excessive lattice strain and large electric field gradients. (C) 19 97 Elsevier Science B.V. All rights reserved.