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Here,we report a new method to directly prepare L10-FePtAu nanoparticles(NPs)from solution synthesis.The unique feature of this synthesis is that oleylamine(OAm)in the synthesis serves as surfactant,solvent and reducing agent at the same time and no other strong reducing agent was used in the synthesis.By simply heating the solution of Fe(acac)3,Pt(acac)2 and gold acetate with OAm to 350 ℃,L10-FePtAu NPs could be directly obtained without further annealing.NP sizes were controlled to be 5.5 to 11.0 nm by changing the amount of Au doping.The highest coervicity of 12.15 kOe at room temperature could be achieved for the NPs with 32％Au doping,which is much higher than the coercivities reported by the previous studies on solution-synthesized FePt NPs.To understand the formation mechanism of L10-FePt phase in the NPs,the synthesis temperature was changed.For 230 ℃ synthesis,only fcc FePt(111)and(200)peaks can be seen,which means that Au atoms entered into the fcc FePt lattice.With increasing the synthesis temperature to 260 ℃,Au peak appeared at the left side of fcc FePt peak,suggesting that Au atoms segregated from fcc FePt lattice.When the synthesis temperature was increased to 290 ℃,L10-FePt peaks can be observed and Au and L10-FePt peaks were completely divided,which means that ordered FePt phase was formed.The NPs synthesized at 230 ℃ show the typical soft magnetic properties.NPs synthesized at 290 ℃ have 5.53 kOe coercivity.Base on these results,it can be concluded that at low temperature synthesis,Fe,Pt and Au atoms nucleated together.With increasing temperature,Au atoms would diffuse out of the fcc FePt lattice,creating lattice vacancies that increase the mobility of Fe and Pt atoms to rearrange to fct phase.