Study On Preparation And Magnetic Properties Of Iron-based Nitride（Cu,In,Zn） NFe₃ With Anti-perovskite Structure

Ternary metal nitride ANM3,as an intermetallic compound,has rich physical properties and potential functional application properties.Since the last century,it has gradually entered people’s field of vision and become the matters of general interest in the field of materials.In this thesis,the iron-based ternary nitride(Cu,In,Zn)NFe3 with anti-perovskite structure is selected as the object of study.Beside,the laboratory preparation process,surface morphology,the relationship between structure types and magnetic properties,and the internal physical mechanism of magnetic behaviors near the magnetic phase transition temperature are systematically studied.By using different chemical elements to substitute the magnetic iron atoms in the parent material γ’-Fe4N,the types and contents of elements in the sample cell were adjusted in an attempt to change its crystal structure and achieve functional optimization.The experimental results of iron-based ternary nitride(Cu,In,Zn)NFe3 included in this thesis provide a certain extent reference for exploring and utilizing this kind of new nitride material.The main achievements can be summarized as follows:1.Series of CuxNFe4_x(0.1≤x≤0.5)samples were successfully prepared by solid-gas reaction method.XRD results showed that all samples showed anti-perovskite cubic crystal structure.With the change of the doping amount of Cu atoms in the samples,the position of diffraction peaks will shift to a certain extent,which indicates that Cu atoms have successfully served as the substitute for Fe atoms in the lattice and makes the lattice constant of materials smaller when unit cells shrink.Cu atoms can successfully dope the parent material γ’-Fe4N and partially enter the crystal lattice as the substitute for the magnetic Fe atoms located at the corner of the cell.Menwhile,the limit of doping is x≤0.5 in CuxNFe4-x.The low-temperature magnetic measurement of the highly doped sample Cu0.5NFe3.5 shows that the Curie temperature of γ’-Fe4N can be reduced by doping with Cu atoms,and the magnetic phase transition temperature of Cu0.5NFe3.5 sample moves to room temperature.The ZFC curve of Cu0.5NFe3.5 sample was obtained when the applied magnetic field was constant at 100 Oe,which showed that the magnetic phase transition occurred near 350 K and the system was still in ferromagnetic ground state.Saturation magnetization value of CuxNFe4_x samples will show certain sensitivity to doping amount.The larger the doping amount x is,the smaller its value is,and the value of the coercive force of samples also shows the same rule.The magnetic permeability of CuxNFe4_x samples will gradually increase with the increase of doping amount x,and the real part of the magnetic permeability of Cu0.5NFe3.5 samples can reach μ’=11.8 at the test frequency of 100 kHz.Meanwhile,the total magnetic loss Pcv decreases gradually when the doping amount x increases.As the increase of Cu doping amount x,the stability of permeability of CuxNFe4_x material in DC bias field can be optimized.2.Series of InxNFe4-x samples were successfully prepared by using nonmagnetic indium(In)atoms instead of magnetic Fe atoms in γ’-Fe4N,and the doping limit was x=0.8.When indium atoms enter the lattice and substitute Fe atoms located at the corner of unit cells,the samples still maintain the face-centered cubic crystal structure type,with a space group of Pm3m.XRD test results show that all diffraction peaks gradually shift to a low angle with the increase of doping amount x of indium atoms,which also indicates that indium atoms have entered the lattice and changed the lattice constant of the material.In this system,the value of lattice constant a fluctuates under the influence of doping amount,and then remains basically unchanged when the doping amount x reaches 0.8.This indirectly indicates the solubility of the parent material γ’-Fe4N doped with in atoms.The low temperature magnetic properties of InxNFe4_x samples were measured,and the results showed that there is a strong correlation between the magnetic phase transition temperature and doping amount,and the Curie temperature of In0.8NFe3.2 with high doping amount is lower than room temperature.The saturation magnetization value of InxNFe4_x samples also shows a positive correlation with its iron atom content.The strengthen spin freezing behavior will happen in the samples at low temperature,and the system will gradually show a spin-glass state.The magnetic measurement and experimental results of In0.6NFe3.4,a highly doped sample,verify the existence of spin-glass behavior in the system and obtain the relevant parameters(T0=73 K,zv=5.51 and τ0=4.26×10-11 s).The spin-glass behavior in this system may be due to the disorder of mixed atoms caused by the doped indium atoms occupying the corner position,or the competition between ferromagnetic and antiferromagnetic interactions.3.For the ZnNFe3 samples successfully prepared by the solid-gas reaction method,the nonmagnetic Zn atoms inside,which like Cu and In atoms,substitute magnetic Fe atoms at the corner position of γ’-Fe4N cells,forming cubic crystal structure phase with space group Pm3m(No.:221).Scanning electron microscope(SEM)pictures of ZnNFe3 samples were taken at 5 um and 10 um scales show that the particles of the samples are evenly distributed and closely arranged,beside,the particle sizes are all distributed in 0.5～1 um.Isothermal magnetic measurements were carried out on ZnNFe3 samples with external magnetic fields at 5 K,300 K and 350 K,respectively.The hysteresis loops obtained show that the saturation magnetization value(Ms)near 108.3 emu/g at 5 K.The hysteresis loop measured at 300 K(room temperature)does not show complete linearity,which indicates that the magnetic system still has weak ferromagnetism.When the test temperature reaches 350 K,the linear hysteresis loop indicates that the sample has completely entered paramagnetic state.The parent material γ’-Fe4N has high saturation magnetization value(Ms～210 emu/g)at room temperature,but its coercive force value is low(Hc～20 Oe)at room temperature.The magnetic properties of ZnNFe3 samples are obviously different,showing the change of magnetic contribution caused by doping atom(Zn).Compared with the parent materialγ’-Fe4N,the ZnNFe3 sample has lower magnetic phase transition temperature,the value of saturation magnetization and coercive force.The magnetic critical behavior and electron spin resonance spectrum of the samples reveal that the ferromagnetic frustration in ZnNFe3 samples comes from the magnetic disorder caused by vacancies on the lattice and the short-range ferromagnetic interaction between different chemical bonds.By analyzing the experimental results of ZnNFe3 samples,it is found that the second-order phase transition process will occur in this system.And when the change range of the applied magnetic field reaches ΔH=50 kOe,the magnetic entropy change value(-ΔSM)of the system can reach 2.2984 J/kg K,furthermore,the relative cooling power(RCP)can reach 247.0671 J/kg,which is close to 47%of the traditional magnetic refrigeration material(Gd).