Preparation And Magnetic Properties Of L1₀-FePt Based Hard Magnetic Nanoparticles

Magnetic nanoparticles are widely used because of their unique physical and chemical properties.Because of its ultrahigh magnetocrystalline anisotropy constant,high curie temperature,minimal superparamagnetic critical size and good chemical and thermal stability,chemically ordered L1₀-FePt has been considered as a candidate for a new generation of high density magnetic storage material.However,FePt which was prepared by physical and chemical method is disorderd soft magnetic phase.Therefore,preparation of FePt-based hard magnetic nanoparticles with high chemical order degree and high magnetic properties has become the focus of the research.In order to obtain the good dispersion of L1₀-FePt nanoparticles,we usually adopt the traditional high temperature organic liquid-phase method.However,the experimental materials used in this method involve more toxic organic reagents and the toxic by-products will be produced in the whole process.In this paper,one-step solid-phase reaction method and galvanic replacement reaction method are environmentally friendly.Above two methods,not only we used the non-toxic inorganic reagents,but also no toxic by-products can be produced.The main contents and results are as follows:?1?In the preparation of L1₀-FePt by solid-phase reaction method,Fe?acac?3,Pt?acac?2,Fe3O4 and PtC l4 were used as precursors.The effects of different Fe,Pt precursors and their ratios on the order degree of L1₀-FePt were studied.When choosing inorganic of Fe3O4 and PtCl4 as the precursors and the molar ratio of Fe and Pt is 1 :1,the prepared L1₀-FePt nanoparticles have the best magnetic properties.Besides,we optimized the mixing mode,calcination temperature,heating rate and the ratio of the insulating medium to salt.It was found that the maximum coercivity of 14.2 kOe can be obtained for the sample annealed at 750? and the ratio of the insulating medium to salt was controlled to be 1500: 1.?2?In order to obtain L1₀-FePt?hard magnetic?/Fe?soft magnetic?nanocomposites,we used Fe nanoparticles and PtC l4 as precursors to prepare the L1₀-FePt/Fe nanocomposites.When the molar ratio of Fe and PtC l4 is 3.3:1,the product is L1₀-FePt/Fe and its magnetic properties are the best.We optimized the reaction time,dropping mode and annealing temperature.When PtC l4 is taken as the half drop and the reaction time for 30 min,its magnetic properties are the best.Its coercivity was 11.5 kOe and saturation magnetization reached to 44.47 emu/g.Futhermore,the product is quite stable in the air.In summary,L1₀-FePt-based hard magnetic nanoparticles were obtained by green experimental schemes.And all of the products have perfect phases and excellent magnetic properties.Besides,these two methods provide important approach for the future preparation and development of magnetic nanoparticles or soft/hard nanocomposites.