Super-fine L1_(0)-Fe Pt nanoparticles(NPs)with high ordering degree were successfully prepared by a modified two-step sintering method,which includes low-temperature pre-sintering,and the high magnetic field(HMF)assis...Super-fine L1_(0)-Fe Pt nanoparticles(NPs)with high ordering degree were successfully prepared by a modified two-step sintering method,which includes low-temperature pre-sintering,and the high magnetic field(HMF)assisted post-sintering processes.The particle size of the L1_(0)-FePt NPs was obviously refined by lowering the sintering temperature.By applying the HMF during the post-sintering process,the fine size characteristics of L1_(0)-Fe Pt NPs were retained,and the ordering degree was significantly improved.The L1_(0)-Fe Pt NPs with sizes of about 4.5 nm,ordering degree of 0.940,and coercivity of 22.01 k Oe were obtained by this two-step sintering under a magnetic field of 12 T.The mechanism investigation of HMF enhancing the ordering degree indicates that the HMF enhances lattice distortion and magnetization energy(Zeeman energy).The enhanced lattice distortions cause high stress existing in the lattice,which can effectively promote the disordered-order transition.When the magnetic field reaches to 3 T,the Zeeman energy of the NPs is higher than the thermal disturbing energy of the NPs,and the magnetization effect is stronger.Therefore,the HMF(higher than 3 T)can obviously improve the disorder-order transition by lowering the energy barrier and accelerating the orderly diffusions of atoms.The HMF is a promising assistant to synthesize the L1_(0)-phase NPs with both of high ordering degree and super-fine size.展开更多
研究了Co含量对熔体快淬Fe_(55-x)Co_xPt_(15)B_(30)(x=0~45,原子分数,%)合金热处理前后的组织结构和磁性能的影响。结果表明,添加Co可提高Fe_(55-x)Co_xPt_(15)B_(30)合金的非晶形成能力,使x=15~45的快淬合金形成非晶态。经适当热处理...研究了Co含量对熔体快淬Fe_(55-x)Co_xPt_(15)B_(30)(x=0~45,原子分数,%)合金热处理前后的组织结构和磁性能的影响。结果表明,添加Co可提高Fe_(55-x)Co_xPt_(15)B_(30)合金的非晶形成能力,使x=15~45的快淬合金形成非晶态。经适当热处理后,合金中形成了由有序面心四方结构的永磁(Fe,Co)-Pt(L1_0)相和软磁(Fe,Co)2B相及(Fe,Co)B相组成的纳米复相组织,显示出永磁性;添加Co的合金组织得到明显细化,x=15~45合金平均晶粒尺寸均约为18 nm;其中x=15合金具有最佳的永磁性能,磁能积达到94.4 k J/m3。合金的矫顽力随Co含量的增加而增大,在x=30时达到最大值413.7 k A/m后,随Co含量的进一步增加而减小;这是由于不同Co含量使L1_0相的c/a值发生变化而导致其磁晶各向异性变化的结果。展开更多
The ordered Pt-based intermetallic nanoparticles(NPs)with small size show superior magnetic or catalytic properties,but the synthesis of these NPs still remains a great challenge due to the requirement of high tempera...The ordered Pt-based intermetallic nanoparticles(NPs)with small size show superior magnetic or catalytic properties,but the synthesis of these NPs still remains a great challenge due to the requirement of high temperature annealing for the formation of the ordered phase,which usually leads to sintering of the NPs.Here,we report a simple approach to directly synthesize monodisperse ordered L1_(0)-FePt NPs with average size 10.7 nm without further annealing or doping the third metal atoms,in which hexadecyltrimethylammonium chloride(CTAC)was found to be the key inducing agent for the thermodynamic growth of the Fe and Pt atoms into the ordered intermetallic structure in the synthetic process.In particular,10.7 nm L1_(0)-FePt NPs synthesized by the proper amount of CTAC show a coercivity of 3.15 kOe and saturation magnetization of 45 emu/g at room temperature.The current CTAC-assisted synthetic strategy makes it possible to deeply understand the formation of the ordered Pt-based intermetallic NP in solution phase synthesis.展开更多
基金financially supported by the National Natural Science Foundation of China(Grant nos.51871045,52071070,and 51690161)the Fundamental Research Funds for the Central Universities(Grant no.N2017003)the Doctoral Start-up Foundation of Liaoning Province(Grant no.2019-BS-116)。
文摘Super-fine L1_(0)-Fe Pt nanoparticles(NPs)with high ordering degree were successfully prepared by a modified two-step sintering method,which includes low-temperature pre-sintering,and the high magnetic field(HMF)assisted post-sintering processes.The particle size of the L1_(0)-FePt NPs was obviously refined by lowering the sintering temperature.By applying the HMF during the post-sintering process,the fine size characteristics of L1_(0)-Fe Pt NPs were retained,and the ordering degree was significantly improved.The L1_(0)-Fe Pt NPs with sizes of about 4.5 nm,ordering degree of 0.940,and coercivity of 22.01 k Oe were obtained by this two-step sintering under a magnetic field of 12 T.The mechanism investigation of HMF enhancing the ordering degree indicates that the HMF enhances lattice distortion and magnetization energy(Zeeman energy).The enhanced lattice distortions cause high stress existing in the lattice,which can effectively promote the disordered-order transition.When the magnetic field reaches to 3 T,the Zeeman energy of the NPs is higher than the thermal disturbing energy of the NPs,and the magnetization effect is stronger.Therefore,the HMF(higher than 3 T)can obviously improve the disorder-order transition by lowering the energy barrier and accelerating the orderly diffusions of atoms.The HMF is a promising assistant to synthesize the L1_(0)-phase NPs with both of high ordering degree and super-fine size.
文摘研究了Co含量对熔体快淬Fe_(55-x)Co_xPt_(15)B_(30)(x=0~45,原子分数,%)合金热处理前后的组织结构和磁性能的影响。结果表明,添加Co可提高Fe_(55-x)Co_xPt_(15)B_(30)合金的非晶形成能力,使x=15~45的快淬合金形成非晶态。经适当热处理后,合金中形成了由有序面心四方结构的永磁(Fe,Co)-Pt(L1_0)相和软磁(Fe,Co)2B相及(Fe,Co)B相组成的纳米复相组织,显示出永磁性;添加Co的合金组织得到明显细化,x=15~45合金平均晶粒尺寸均约为18 nm;其中x=15合金具有最佳的永磁性能,磁能积达到94.4 k J/m3。合金的矫顽力随Co含量的增加而增大,在x=30时达到最大值413.7 k A/m后,随Co含量的进一步增加而减小;这是由于不同Co含量使L1_0相的c/a值发生变化而导致其磁晶各向异性变化的结果。
基金supported by the National Natural Science Foundation of China under Grant(Nos.51871078,51631001 and 51590882)the National Key R&D Program of China(No.2016YFA0200102)Heilongjiang Science Foundation(No.E2018028).
文摘The ordered Pt-based intermetallic nanoparticles(NPs)with small size show superior magnetic or catalytic properties,but the synthesis of these NPs still remains a great challenge due to the requirement of high temperature annealing for the formation of the ordered phase,which usually leads to sintering of the NPs.Here,we report a simple approach to directly synthesize monodisperse ordered L1_(0)-FePt NPs with average size 10.7 nm without further annealing or doping the third metal atoms,in which hexadecyltrimethylammonium chloride(CTAC)was found to be the key inducing agent for the thermodynamic growth of the Fe and Pt atoms into the ordered intermetallic structure in the synthetic process.In particular,10.7 nm L1_(0)-FePt NPs synthesized by the proper amount of CTAC show a coercivity of 3.15 kOe and saturation magnetization of 45 emu/g at room temperature.The current CTAC-assisted synthetic strategy makes it possible to deeply understand the formation of the ordered Pt-based intermetallic NP in solution phase synthesis.
