The Theoretical Calculation Of The New Rare Earth Permanent Magnet Materials And Diffraction Experiments To Study

The anomalous thermal expansion of R(Fe,Mo)₁2 compounds, the substituted effects of Si and N in the R(Fe,Si)₁2 compounds and micro-mechanism of Nd(Fe,Si)₁1C_x compounds are studied by the X-ray diffraction in different temperature, the full-potential linearized augmented plane wave (LAPW) and local orbital (lo) based on standard APW method and the neutron powder diffraction methods in this thesis. The mainly novel results are as follows:1. The abnormally thermal expansion of R(Fe, Mo)₁2 compounds mainly determined by Fe-Fe interaction. According to structural parameters of Nd(Fe, Mo)₁2, the anomaly is contributed not only by the short Fe-Fe interaction as the previous explanation on other R-Fe intermetallic compounds but also by the other strongly positive Fe-Fe interactions. The mechanism of substitutes by Mo affecting the thermal expansion anomalies is also discussed.2. The calculation of R(Fe,Si)₁2 compounds (R=Y, Nd) shows that the saturation magnetic moment of RFe₁0Si₂(R=Y, Nd) is larger than the RFe₁0M₂(M=Ti, V, Cr, Mn, Mo å'Œ W), there are two hybridization mechanism in the compounds, Si(8j) reduces the magnetic moment of Fe in three sites, but Si(8f) mainly reduces the magnetic moment of Fe(8i) and Fe(8j) atoms and the Curie temperature is markedly enhanced by the introduction of Si atom according to the varieties of density of state in Fermi surface.3. The neutron powder diffraction experimental results show that there is about 11° angle between the easy magnetization direction and ab plane in the DyFe₁0Si₂ at 77K temperature. The function of N in the compounds according to the calculations will enhance saturation magnetization in the DyFe₁0Si₂N, but the effect is very weak. When Fe(8j) is substituted by the Si atom, The N atom will weaken increasing effects of Fe(8f) magnetic moment and decreased the magnetic moment of Fe(8i).4. The calculation of state densities and magnetic moments in NdFe₉Si₂Cx compounds (X=0,2) shows that the Si atom mainly hybridizes with Fe(4b) and Fe(32i), thereby decreases the Fe magnetic moment. The C atom decreases farther the Fe(32i) magnetic moment and the substituted effects of Si atom, this increases the Fe(4b) magnetic moment.