Interstitial Effect Studies On Rare-Earth Iron Permanent Magnetic Compounds

The effects of interstitial nitrogen, carbon and hydrogen atoms on the structures and magnetic properties of the types of R2Fei4B, Pr(Fe,V)i2, R(Fe,Mo)i2 and RCFe.SOuQ^Y, Nd, Pr and Ce) intermetallic compounds are systematically investigated in this thesis, the methods used are neutron powder diffraction, X-ray diffraction, gas-solid phase reaction analysis, magnetic measurements, magnetocrystalline anisotropy calculation and LMTO-ASA electronic structure calculation.(1) In R2Fei4BNx compounds, Nitrogen atoms are found to enter 4e(0, 0, z) and 4f(x, x, 0) interstitial sites. After nitrogenation, the anti-oxidation ability and Curie temperatures are increased, the average magnetic moments of iron atoms are decreased by 2 to 3 percent, the magnetocrystalline anisotropy of iron sub-lattice changes very little while that of the rare-earth sub-lattice decreases so that lower the spin reorientation temperatures. The change of magnetocrystalline anisotropy corresponds to the result of single ionic model calculation, which shows the absolute value of the second order crystalline field parameter of Pr2Pe14B compound decreases with increasing of nitrogen content. The electronic structure calculation shows, the magnetic moments of Fe (4c), Fe (8ji) and Fe (16k2) are lowered, while the magnetic moments of Fe (4e) are increased.By insertion of hydrogen atoms into the Y2Fei4B compound, the Curie temperature and saturation magnetization are increased while the magnetocrystalline anisotropy is decreased.(2) In the Pr(Fe,V)i2 compound and its nitride, V and Mo atoms are found to occupy the Si-substitute site, and nitrogen atoms to enter the 2b interstitial site. By nitrogenation, the saturation magnetization and Curie temperature are increased, the easy-magnetization orientation is changed to align c-axis, which is in agreement with the calculated result that, the magnetocrystalline anisotropy constant KI of rare-earth sub-lattice is changed from negative to positive. Pr(Fe,V)i2-type nitrides are found to have high Curie temperature, large saturation magnetization, low price and better magnetic properties at low temperature, therefor Pr(Fe,V)12Nx compounds hold significant promise as a competitor to Nd2Fci4B.(3) In the arc-melted YFe10.sMoi.5Cx compounds, most of the carbon atoms are found to enter the interstitial 2b sites and have similar effect onthe magnetic properties with nitrogen atoms. While in the PrFeio.sMoi.iCo.4 compound, it is found that most of the carbon atoms occupy the 8i site, the residual carbon atoms enter the 2b site, the magnetocrystalline anisotropy remains easy-planer. The arc-melted Pr(Fe,Mo)i2Cx compounds are also suitable for permanent magnetic applications and are stable at higher temperature.(4) R(Fe,Si)nCx and their hydrides are found to have BaCdn-type tetragonal structure, silicon atoms prefer the 8d site and carbon atoms enter the 8c interstitial site. Because of the low overlap extent of the Fe-Fe neighboring electronic clouds, the moments of iron atoms are small and the Curie temperatures are low. The magnetocrystalline anisotropy of the iron sub-lattice and rare-earth ions such as Nd3+ are easy-planer. Hydrogen atoms are found to enter 3 interstitial sites, increase the Curie temperature and average moments of iron atoms, while decrease the magnetocrystalline anisotropy of iron sub-lattice.