Preparation And Characterization Of FePt、CoPt Magnetic Nanoparticles And Structure Of FePt/Co Nanocomposite

The areal density of hard disk drives has sharply increased in the past ten years,which is ascribed to continuous research and development of recording heads and media.However,the present areal density is below 10Tb/in2 due to the technical bottlenecks uch as superparamagnetism.To overcome this bottleneck,many researchers pay much attention to magnetic nanoparticles with extremely high magnetocrystalline anisotropy,such as chemically order L10 phase FePt or CoPt nanoparticles.These nanoparticles exhibit high magnetocrystalline anisotropy(Ku>5x107ergs/cm3).Even though the grain size is reduced down to 3–5 nm,the magnetic energy(KuV)is still more than thermalenergy(KBT).Meantime,FePt、CoPt nanoparticles,with L10-ordered structure,serve as the leading candidates for hard magnetic phase in the permanent magnetic nanocomposites,also become an interesting topic because of their large magnetocrystalline anisotropy,chemical stability and high coercivity.Besides FePt and CoPt exhibit higher Ku,CoPt shows good resistance to corrosion and oxidation,which is more fit to practical application.However,the as-prepared particles have FCC A1 crystal structure,which is a soft ferromagnetic phase.The FCT L10 hard magnetic phase which we desired can be obtained only after high temperature annealing above 600 oC.In this work,the CoPt nanoparticles are firstly prepared by liquid phase method。But,the preparation of nanoparticles often requires more experiental steps and high temperature annealing,which always leads to particle agglomeration.Therefore,direct preparation FCT phase FePt nanoparticle by solid-phase sintering method has been proposed.That is,L10-FePt/CoPt nanocomposites,with good disperse and uniformed size,were obtained by ball milling the mixture of precursors(Fe、Co and Pt)and NaCl,followed by heat-treatment at different temperatures under a reductive atmosphere flow.These nanoparticles were coated uniformly by soft magnetic phasederived from the thermal decomposition of soft magnetic phase cobalt source precursor CoCl2·6H2O,then obtained the high-performance permanent magnetic FePt/Co nanocomposites.This article also researches the effect of different substrates on the structure and magnetic properties of FePt nanoparticles.VSM,XRD,TEM analysis were employed to characterize magnetic properties,crystal structure,morphology and structure.The main contents and results are as follows:1.CoPt nanoparticles were prepared with high temperature liquid phase method.The average particle size was about 5.2nm for the sample by reduction of Co2(CO)8 and Pt(acac)2 which have chemical disorder of a face-centered tetragonal(FCC)phase nanoparticles.2、FCT phase FePt and CoPt nanoparticles were prepared directly by solid-phase sintering method.The proportions of NaCl and Fe,Pt precursor is fixed as 1500:1.Moreover,the effect of different substrates such as NaCl,CaO,C,Al2O3,KCl and KN on the structure and magnetic properties of FePt nanoparticles.KCl and Al2O3 hinder the formation of FePt phase and decrease the magnetic properties.NaCl is the best substrate.3、Prepared FePt nanocomposites with good disperse and uniformed size by soild phase method.These nanoparticles were then coated uniformly by soft magnetic phasederived from the thermal decomposition of soft magnetic phase cobalt source precursor CoCl2·6H2O,then obtained the high-performance permanent magnetic FePt/Co nanocomposites,with the large Hc of about 8.4kOe,Ms 31.147 emu/g.