NANOCRYSTALLINE MAGNETITE - Fe₃O₄ PARTICLES SYNTHESIZED BY MECHANICAL MILLING

Abstract

Nanocrystalline magnetite – Fe₃O₄ has been synthesized in nanocrystalline state by mechanical milling of well crystallized magnetite samples obtained by heat treatment of a stoichiometric mixture of iron and hematite. Upon increasing the milling time, the mean crystallite size of magnetite is diminishing. After only 5 minutes of mechanical milling the crystallites are 110 nm. The milling up to 120 minutes leads to a continuous reduction of crystallites size up to 8 nm. The mechanical milling process induces strains into the lattice and the lattice strains increase drastically in the first 60 minutes of milling, after that a saturation of lattice strains is noticed. During milling a contamination of the powder with elemental iron occurs for milling times larger than 30 minutes. A decrease of the saturation magnetisation is noticed upon increasing the milling time and the decrease is associated with the structural disorder and defects that are induced into the material during milling. A tendency of the magnetisation to become unsaturated is also noticed and it is related to canted spins effect.