Magnetic properties of magnetite prepared by ball-milling of hematite withiron

Magnetic properties of magnetite powder prepared by ball-milling of stoichi ometric mixture of hematite and iron in an inert atmosphere are reported. H ysteresis loops, isothermal remanence acquisition curves and temperature de pendence of magnetic susceptibility measurements are used to characterise t his material and to examine the effects of heating in air and in an argon a tmosphere. Ball-milling of hematite with iron during periods ranging from 3 0 min up to almost 5 h yields magnetite which exhibits high magnetic hardne ss, characterised by coercive force three times higher than that typical fo r single-domain natural magnetites. However, the magnetite produced is unst able upon heating in air, reoxidising almost completely to hematite. Heatin g in an argon atmosphere causes enhancement of typical magnetic parameters, but decreases the magnetic hardness. (C) 2000 Elsevier Science B.V. All ri ghts reserved.