Thmn <sub> 12 </ Sub> The Type Ndfen Of Rare Earth - Iron Gap Compounds And Performance Research

As one new generation of rare-earth permanent magnetic materials, NdFeN possesses potential applications in computer, communication, car, medical equipment, et al. In this thesis, theoretically, magnetic moment and density of states(DOS) of NdFe₁₂N were calculated by local spin density approximation method based on density functional theory. And then, the influences of nitrogen-doping on the magnetic moment and DOS of NdFe₁₂N and YFe₁₂N were explored. Experimentally, NdFe_12-xMo_xN_y magnetic powder was prepared by mechanical alloying. Effects of Mo content, ball-milling time, annealing temperature, annealing time, nitridation temperature and nitridation time on the microstructure and the magnetic properties of NdFe_12-xMo_xN_y magnetic powder were explored systematically.The calculation results indicate that NdFe₁₂N magnetic moment is mainly originated from transition metal atom Fe. The magnetic moment of Fe atoms varies dramatically at different local coordination, which is resulted from the different nearest neighbor atoms. DOS of NdFe₁₂N at Fermi level is high and two major peaks are separated by the Fermi level at the minority spin states, which explains that the structure of NdFe₁₂N is unstable and adding stable element is necessary.The experimental results show that the stability of Nd(Fe,Mo)₁₂ phase is improved by the doping of element Mo into the alloys, but excessive Mo content may result in low magnetic properties. The optimal magnetic properties of NdFe_12-xMo_x can be achieved when the x of Mo content is about 1.5. NdFe_12-xMo_x magnetic powder prepared by high energy ball-milling is mainly composed of the amorphous phase and nano-crystallineα-Fe phase. The mechanism of the amorphous phase formation is melting-rapid solidification process during ball-milling. Magnetic properties of NdFe_12-xMo_x increase with the increase of ball-milling time. Annealing temperature and time remarkably affect the microstructure and the grain size of Nd(Fe,Mo)₁₂ phase. At lower annealing temperature and in shorter annealing time, NdFe_12-xMo_x magnetic powder can not be completely crystallization, which results in low magnetic properties. However, too high annealing temperature and too long annealing time would results in the excessive growth of Nd(Fe,Mo)₁₂ grains, which also results in low magnetic properties. Lattice expansion caused by nitrogen-doping can obviously improve the microstructure and the magnetic properties of Nd(Fe,Mo)₁₂ magnetic powder. Nitridation temperature and time play crucial roles in nitrogen-doping procedure. Lattice interspaces of Nd(Fe,Mo)₁₂ are not occupied by N atoms completely at lower nitridation temperature and in shorter nitridation time. However, too high nitridation temperature and too long nitridation time would result in the increase ofα-Fe phase and the decrease of NdFe_12-xMo_x magnetic properties.The optimal preparing parameters of NdFeN magnetic powder are as follow, 16h of ball-milling time, 900℃of annealing temperature, 120min of annealing time, 550℃of nitridation temperature and 2h of nitridation time. The magnetic properties of NdFe_10.5Mo_1.5N_0.9 magnetic powder prepared by optimal procedure are 0.541T of B_r, 780.6kA/m of H_cj, 63.54kJ/m³ of (BH)_max.