| L10-FePt is an important functional material because of its extremely high magnetocrystalline anisotropy,good biocompatibility and excellent catalytic activity.However,it’s difficult to directly synthesize L10-FePt nanoparticles with uniform granularity and high ordering by wet-chemical method.According to previous works,FePt nanoparticles with a certain ordering degree could be prepared by doping the third metal element during preparation.To further increase the ordering degree of nanoparticles,an in-depth study on the mechanism of the third elements promoting ordering should be carried out.However,due to the limitation of experimental research,it is difficult to reveal the mechanism of doping promoting ordered transformation.First principle is a helpful tool to study structure of materials.Based on above background,first principle was employed to investigate ordered transformation of FePt nanoparticles in this work.The VASP software is used to perform a series of calculations on the Ag/Cu/Pb doping,vacancy defects,Ag/Cu/Pb doping and vacancy defects coexistence in ordered and disordered FePt.The calculation models and parameters are verified via the combination of experiment and calculation.The effects of doping and vacancy defects on FePt alloy are studied based on structure,formation energy,magnetic properties,charge density difference,ordered transformation temperature and so on.According to lots of simulations and calculations,some valuable achievements have been obtained.This work provides theoretical basis for one-step chemical synthesis and practical application of Ll0-FePt nanoparticles,and has important research significance.The FePt alloy with Ag/Cu/Pb doping concentration of 3.125%and 6.25%are calculated and analyzed,respectively.The results show that single doping is easier to form at the Fe site,while double doping is easier to form at the near Fe sites.The doping has less impact on saturation magnetization.Doping can effectively decrease the temperature of ordered tranformation.The tranformation temperature decreases with the increase of doping concentration.Furthermore,Pb doping has the strongest promotion on ordering,which can obviously reduce the ordered tranformation temperature to 701 K.The FePt alloy with vacancy concentrations of 3.125%and 6.25%are calculated and analyzed,respectively.The results indicate that single vacancy is easier to form at the Fe site,while divacancy is easier to form at the far Fe sites.Vacancy defects can effectively decrease the ordered tranformation temperature.The ordered tranformation temperature of single vacancy is 1112 K,which is lower than that of single doping.The ordered tranformation temperature of divacancy is 759 K,which is lower than that of Cu/Ag double doping,but slightly higher than that of Pb double doping.The models of single vacancy are built based on that of Ag/Cu/Pb doping.Simulations and calculations indicate that Cu,Ag and Pb doping can effectively decrease vacancy formation energy in FePt system,which induces the formation of vacancy.The co-defects of doping and vacancy can significantly decrease the ordered tranformation temperature.The lowest ordered tranformation temperature is 683 K for Pb and vacancy double defects,the second lowest is 781 K for Ag and vacancy double defects and the highest is 837 K for Cu and vacancy double defects.In summary,the introduction of defects increases the formation energy of both disordered and ordered systems.However,the difference of formation energy and the energy barrier of phase tranformation are decreased due to the different impact trends,which can reduce the ordered tranformation temperature and promote the ordering process.The promotion of vacancy defects on ordering is stronger than that of doping.Doping can promote the formation of vacancy defects via decreasing vacancy formation energy,which accelerates the reordering of Fe and Pt atoms and forms an ordered phase.Therefore,the third metal element doping is an effective method in experimental preparation. |
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